Science, Irving K. Barber Faculty of (Okanagan)
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Biology, Department of (Okanagan)
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Movement Ecology. 2021 Mar 17;9(1):10
The Author(s)
Mancuso, Kristen A.
Fylling, Megan A
Bishop, Christine A
Hodges, Karen E.
Lancaster, Michael B
Stone, Katharine R
Background: For many songbirds in North America, we lack movement details about the full annual cycle, notably outside the breeding season. Understanding how populations are linked spatially between breeding and overwintering periods (migratory connectivity) is crucial to songbird conservation and management. We assessed migratory connectivity for 2 breeding populations of Gray Catbirds (Dumetella carolinensis) west of and within the Rocky Mountains by determining migration routes, stopover sites, and overwintering locations. Additionally, we compared apparent annual survivorship for both populations. Methods: We deployed 39 archival light-level geolocators and 21 Global Positioning System (GPS) tags on catbirds in the South Okanagan Valley, British Columbia, Canada, and 32 geolocators and 52 GPS tags in the Bitterroot River Valley, Montana, USA. These devices allowed us to determine migration routes, stopover sites, overwintering locations, and migratory connectivity. Migratory connectivity was quantified using Mantel’s correlation. We used mark-recapture of colour banded catbirds in both sites to estimate apparent annual survivorship. Results: We retrieved 6 geolocators and 19 GPS tags with usable data. Gray Catbirds from both populations passed through the Rocky Mountains eastward before heading south towards their overwintering locations in northeastern Mexico and Texas. Stopover sites during fall migration occurred primarily in Montana, Kansas, Oklahoma, and Arkansas. Overwintering locations spanned Texas and 5 states in northeastern Mexico. Individual catbirds used up to 4 distinct sites during the overwintering period. Catbirds separated by almost 500 km during the breeding season overlapped during the non-breeding season, suggesting weak migratory connectivity among western populations (Mantel’s correlation = 0.013, P-value = 0.41). Catbird apparent annual survivorship estimates were higher in British Columbia (0.61 ± 0.06 females; 0.64 ± 0.05 males) than in Montana (0.34 ± 0.05 females; 0.43 ± 0.04 males), though the main driver of these differences remain unclear. Conclusions: Our results provide high precision geographic details during the breeding, migration, and overwintering phases of the annual cycle for western Gray Catbirds. Notably, we found that western catbirds followed the Central Flyway as opposed to the Pacific Flyway. We document that catbirds used multiple sites over winter, contrary to the popular belief that this phase of the annual cycle is stationary for most songbirds.
RESEARCH Open AccessMigration ecology of western gray catbirdsKristen A. Mancuso1* , Megan A. Fylling2, Christine A. Bishop3, Karen E. Hodges1,Michael B. Lancaster4 and Katharine R. Stone5AbstractBackground: For many songbirds in North America, we lack movement details about the full annual cycle, notablyoutside the breeding season. Understanding how populations are linked spatially between breeding andoverwintering periods (migratory connectivity) is crucial to songbird conservation and management. We assessedmigratory connectivity for 2 breeding populations of Gray Catbirds (Dumetella carolinensis) west of and within theRocky Mountains by determining migration routes, stopover sites, and overwintering locations. Additionally, wecompared apparent annual survivorship for both populations.Methods: We deployed 39 archival light-level geolocators and 21 Global Positioning System (GPS) tags on catbirdsin the South Okanagan Valley, British Columbia, Canada, and 32 geolocators and 52 GPS tags in the Bitterroot RiverValley, Montana, USA. These devices allowed us to determine migration routes, stopover sites, overwinteringlocations, and migratory connectivity. Migratory connectivity was quantified using Mantel’s correlation. We usedmark-recapture of colour banded catbirds in both sites to estimate apparent annual survivorship.Results: We retrieved 6 geolocators and 19 GPS tags with usable data. Gray Catbirds from both populations passedthrough the Rocky Mountains eastward before heading south towards their overwintering locations in northeasternMexico and Texas. Stopover sites during fall migration occurred primarily in Montana, Kansas, Oklahoma, andArkansas. Overwintering locations spanned Texas and 5 states in northeastern Mexico. Individual catbirds used upto 4 distinct sites during the overwintering period. Catbirds separated by almost 500 km during the breedingseason overlapped during the non-breeding season, suggesting weak migratory connectivity among westernpopulations (Mantel’s correlation = 0.013, P-value = 0.41). Catbird apparent annual survivorship estimates werehigher in British Columbia (0.61 ± 0.06 females; 0.64 ± 0.05 males) than in Montana (0.34 ± 0.05 females; 0.43 ± 0.04males), though the main driver of these differences remain unclear.Conclusions: Our results provide high precision geographic details during the breeding, migration, andoverwintering phases of the annual cycle for western Gray Catbirds. Notably, we found that western catbirdsfollowed the Central Flyway as opposed to the Pacific Flyway. We document that catbirds used multiple sites overwinter, contrary to the popular belief that this phase of the annual cycle is stationary for most songbirds.Keywords: Dumetella carolinensis, Full annual cycle, Migration, Migratory connectivity, GPS tracking© The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License,which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you giveappropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate ifchanges were made. The images or other third party material in this article are included in the article's Creative Commonslicence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commonslicence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtainpermission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to thedata made available in this article, unless otherwise stated in a credit line to the data.* Correspondence: kmancuso88@gmail.com1Department of Biology, University of British Columbia Okanagan, Kelowna,British Columbia, CanadaFull list of author information is available at the end of the articleMancuso et al. Movement Ecology (2021) 9:10 https://doi.org/10.1186/s40462-021-00249-7BackgroundThe decline of North American songbirds is a conserva-tion concern in the Anthropocene [1, 2]. There aremajor knowledge gaps in the ecology of most migratorybird species, with deficits evident especially during mi-gration and winter because most research is focused onbreeding birds [2–5]. The link through space and timebetween breeding and overwintering periods is import-ant to address, in part because the effects in one seasoncan influence events in another season, such as habitatquality influencing body condition and migration timing[5, 6]. The full annual cycle of migrant songbirds gener-ally includes breeding, fall migration, overwintering, andspring migration. To identify potential threats through-out the annual cycle, it is important to understandwhere, when, and how long a bird is present at eachstage of the cycle [7, 8].Conservation and management efforts for songbirdsrequire an understanding of how populations are geo-graphically linked through different phases of the annualcycle – a concept termed migratory connectivity [7, 9].Individuals from populations of species with strong mi-gratory connectivity show minimal geographic spreadand little overlap with other populations through differ-ent phases of the annual cycle, whereas individuals frompopulations of species with weak migratory connectivityshow greater geographic spread and may co-occur withindividuals from different populations [7, 9]. Conse-quently, a threat on the overwintering grounds may havediffuse effects among multiple populations if weak mi-gratory connectivity exists [7, 10]. However, it may bemore challenging to implement effective conservationstrategies across the annual cycle for populations withweak migratory connectivity.In addition to studying population-level characteristicsof a species, apparent annual survivorship is a valuabledemographic rate because it can indicate the health of apopulation, life cycle stages at risk, and identify high-quality habitat [11, 12]. Survivorship is sensitive toshort-term and local environmental changes and, there-fore, can help elucidate the underlying mechanisms tochanges in population size [11, 12]. However, robust an-nual survivorship estimates can be challenging to obtainas they require multiple years of data on markedindividuals.In this study, we examined the migration behaviourand estimated apparent annual survivorship of Gray Cat-birds (Dumetella carolinensis) breeding west of andwithin the Rocky Mountain Range. Gray Catbirds arethe only species within the Mimidae family whose mi-gratory behaviour has been studied in detail but only inthe eastern portion of its extensive North Americanrange [13]. The known overwintering range of Gray Cat-birds includes Florida, southeastern Texas, southeasternLouisiana, eastern Mexico, and Central America [14]. Inthe eastern and central portion of the breeding range,Ryder et al. [13] found catbirds breeding in the mid-Atlantic overwintered in Cuba and Florida, and thosebreeding in the Midwest overwintered in Central Amer-ica. Likewise, stopover ecology is limited to eastern pop-ulations; one mark-recapture study in coastal Alabamaduring fall migration reported adult catbirds stayed onaverage for 4.1 days before departure [15].The migration ecology of western Gray Catbirds, in-cluding how they travel through or around the RockyMountain Range, remains unexplored. Most migratorybirds breeding west of the mountains migrate using thePacific Flyway, whereas most birds east of the mountainsfollow the Central Flyway [16–19]. However, studiesfrom central and coastal British Columbia trackedbreeding Veeries (Catharus fuscescens) and Swainson’sThrushes (C. ustulatus) across the Rocky Mountains tothe Central Flyway towards overwintering sites in SouthAmerica [20–22]. In 1964, it was postulated that westernGray Catbirds may migrate east before heading south,implying that these birds have to cross the Rocky Moun-tains [23]. Similarly, the analyses of stable hydrogen iso-tope ratios of catbird feathers linked overwintering birdsin Mexico to inferred breeding sites located in thenorthwestern part of their breeding range [24].The goals of our research on Gray Catbirds were to:(1) track migration routes; (2) identify stopover sites; (3)determine overwintering locations; (4) assess migratoryconnectivity; and (5) compare apparent survivorship forpopulations breeding in western Montana, USA, andsouthern British Columbia, Canada. Our research willverify whether western Gray Catbirds migrate using thePacific Flyway or the Central Flyway. In addition, we willadvance our understanding of the full annual cycle ofwestern catbird populations and their migration ecologywhich may help ensure this species remains abundanton the landscape.MethodsStudy areasWe examined breeding Gray Catbirds in two locations:(1) the South Okanagan Valley, British Columbia,Canada (49.200° N, 119.552° W), and (2) the BitterrootRiver Valley, Montana, USA (46.668° N, 114.023° W).These two study areas were 495 km apart, with the Brit-ish Columbia population occurring west of the RockyMountains and the Montana population occurringwithin the Rocky Mountains. Catbirds were locally abun-dant in both study sites.Tracking devicesGray Catbirds were captured in mist-nets passively orwith the aid of call-playback in the breeding seasonsMancuso et al. Movement Ecology (2021) 9:10 Page 2 of 16from 2013 to 2018. Each bird was given a standardUSGS band and a unique combination of colour-bandsto aid in future identification. Birds were aged and sexedaccording to Pyle (1997) [25]. Adult male and femalecatbirds were outfitted with an M-Series light-level geo-locator, Lotek, Newmarket, Canada (mass between 0.3–1.0 g, hereafter “geolocator”) or PinPoint GPS tag, Lotek,Newmarket, Canada, (mass 1.0 g, hereafter “GPS tag”[26, 27]). Geolocators were used only to infer generalmovement patterns whereas GPS tags were used formovement patterns plus quantitative analyses.Tracking devices were fitted onto birds by creating aleg-loop harness which allowed the device to sit on thelower back of the bird, an optimal position for sunlightand satellite communication [28]. The harness was madeof Stretch Magic jewelry cord manufactured by PepperellBraiding Company, MA. Stretch Magic is an elastic-like,transparent, monofilament made of polyurethane andpolyester and was ideal for accommodating fluctuationsin size throughout the year. The harnesses were closedeither by using a crimp bead or melting with a solderingiron, allowing harnesses to be custom fit to birds ofvarying sizes. Throughout the project, we checked recap-tured birds for any sign of wear, abrasion, or feather lossand found minimal undesirable effects, however, somebirds had evidence of light chafing on their thighs. Har-nesses were durable and we had no instances of birdslosing their geolocators or GPS tags with this method.This technique was adopted from other researchers whoused the method successfully for attaching geolocatorsto songbirds [29, 30].The average mass of Gray Catbirds was 36.3 g, there-fore, tracking devices were < 3% of body mass, which isthe preferred maximum for tracking birds and withinthe < 5% recommendation by animal care committeestandards [31, 32]. Due to the small size of the devices,the number of GPS fixes were limited, with up to 8 fixesadvertised for PinPoint-8 tags, up 10 fixes advertised forPinPoint-10 tags, and up to 80 fixes advertised for SwiftPinPoint-10 tags [33]. Devices were retrieved in subse-quent breeding seasons by targeting individuals identi-fied by their unique colour-band combination. Capturedbirds had the harness and device removed then releasedunharmed. We deployed 39 geolocators and 21 GPS tagsin British Columbia, and 32 geolocators and 52 GPS de-vices in Montana.The average accuracy (± standard deviation) of the M-Series geolocator is 185 (±115) km, but many factorsmay affect the accuracy of geolocators, including shad-ing, clouds, sensor degradation, and artificial lights [34].The shrubby riparian habitat inhabited by Gray Catbirdsmay be an additional source of shade and further limitgeolocator accuracy. The accuracy of GPS tags varies de-pending on the number of satellites available during ascheduled fix, however, in all cases should be better than300 m [33]. We tested the GPS tags before deploymentin British Columbia at a stationary location and foundthat 90% of the points were within 100 m of the test lo-cation, and many within a few meters. GPS tags werepre-programmed to obtain GPS coordinates at specificdates, which varied by location and year but generallywere 1–5 days apart during migration and 10–30 daysapart during winter.Repeat trackingThree Montana birds were tracked in multiple yearswith separate devices. One female catbird was given ageolocator in 2012, another geolocator in 2013, and aGPS tag in 2014. One male catbird was given a geoloca-tor in 2013 and a GPS tag in 2014. Another male catbirdwas given a GPS tag in 2016 and another GPS tag in2017.Analyses of tracking devicesGeolocator files (.lig) were downloaded and light datawere processed using R (v 3.5.1 [35]). Methods for theanalyses of the geolocators followed Lisovski et al.(2020) [36]. We used the GeoLight (v. 2.0.1 [37]),TwGeos (v.0.1.2 [38]), and adehabitatHR (v. 0.4.16 [39])packages. Twilights were determined using the prepro-cessLight function in the TwGeos package using athreshold value of 0.5 because there did not appear to beany nighttime light interference. Twilights were editedusing the twilightEdit function from the TwGeos pack-age (with ‘window’ set to 4, ‘outlier.mins’ set to 45, and‘stationary.mins’ set to 25). Overwintering dates were de-fined as November 15 – March 1 to avoid the equinoxby 3 weeks and to include times when birds would be ontheir wintering grounds [40]. The Hill-Ekstrom methodwas used to determine the sun elevation angle duringwinter months using the findHEZenith function fromthe TwGeos package [41, 42]. The Hill-Ekstrom methoddetermines the correct sun elevation angle for stationaryperiods at unknown locations by determining a sun ele-vation angle that minimizes variance in latitude esti-mates [43]. Winter latitude and longitude estimates werecalculated using the coord function of Geolight. Tosummarize the overwintering locations used by GrayCatbirds, 50% Kernel Density estimates were calculatedfrom coordinates using the kernelUD function from theadehabitatHR package. A shapefile compatible with Arc-Map 10.7.1 [44] was created by using the getverticeshrfunction.The location coordinates from the GPS tags were vet-ted by removing points that had low accuracy, defined asthose with dilution of precision values greater than 20[33]. The remaining points were plotted using Arc-Map 10.7.1. Points were connected to create migrationMancuso et al. Movement Ecology (2021) 9:10 Page 3 of 16tracks and to calculate distances, although we cautionthat these straight-line paths are our best approximationof migration route as the exact path is unknown. We de-fined stopover sites as locations with 2 or more consecu-tive fixes during migration outside of the mapped non-breeding range in September and early October. GPSfixes were programmed to be taken between 1 and 5days apart, therefore, the minimum stationary periodduring migration that we considered a stopover was 24h. Overwintering locations were defined as the first sta-tionary period of consecutive fixes in the known over-wintering range. However, for the older generation GPStags where 8 or fewer fixes were obtained, we assumethat the points occurring from mid-October onwardscorrespond to overwintering locations, as most GPS-tagged birds from both sites had reached their overwin-tering locations by early October based on the latermodel Swift GPS tags. To visualize potential travelroutes around or within the Rocky Mountains, tracksand points were overlaid on a 30 arc-second digital ele-vation model of North America in ArcMap 10.7.1 [44].To better contextualize habitat and elevation at stopoverlocations and overwintering locations, we overlaid satel-lite imagery using ArcMap 10.7.1 for each catbird duringstopovers and in the non-breeding period.Migratory connectivityMigratory connectivity was quantified with a Mantel’scorrelation (rM) which involves comparing two matricesand their random permutations [45]. A significant posi-tive correlation in the distances between breeding indi-viduals and overwintering individuals suggests strongmigratory connectivity [46]. Our matrices included (1)the geographic distances between all individuals on thebreeding ground and (2) the geographic distances be-tween all individuals on the overwintering grounds. Be-cause some catbirds moved around during theoverwintering period and we did not have data for thefull overwintering period for all birds, we used the firstoverwintering location for the second matrix. Note thatonly geographic locations from GPS tags were includedin the distance matrices and not locations obtained bygeolocators due to the inherent low precision associatedwith geolocators. Matrices were created using the r.dis-t.earth function of the fields package (v.9.8.6 [47]) in R.The Mantel correlation coefficient was calculated usingthe mantel.rtest function of the ade4 package (v.1.7.13[48]). A P-value associated with the correlation coeffi-cient was calculated based on 9999 random permuta-tions. In addition to Mantel’s correlation, we calculatedthe average pairwise distances between all individualswithin the breeding and overwintering locations separ-ately for Montana and British Columbia birds to quan-tify the geographic spread of each population.Apparent annual survivorshipWe included both recaptured and resighted birds in ourapparent annual survivorship analyses. In BritishColumbia, the data set spanned 2015 to 2019 and a totalof 537 birds were colour-banded. Two study sites inBritish Columbia were used and effort included (1) inter-mittent target and passive mist-netting in conjunctionwith deploying and retrieving tracking devices; and (2) astandardized approach. Target and passive netting in-volved setting up 1–8 nets from before sunrise to earlyafternoon at the latest and occurred intermittently (~ 1–3 times a week) between May–August. Concurrently, 1–3 biologists searched for birds using binoculars and con-firmed colour-band combinations using high-zoomdigital cameras or binoculars. Effort was increased dur-ing the last year of the study in 2019, where at least 5days a week, catbirds were resighted or recaptured fromthe end of May to early July. The standardized approachoccurred once a week between May 1–September 15using 10 mist-nets in a fixed location for 6 h and oc-curred in the first site only.In Montana, the dataset spanned 2006 to 2018 and atotal of 741 catbirds were colour-banded. Two studysites in Montana were used and effort included (1) inter-mittent target and passive mist-netting in conjunctionwith deploying and retrieving tracking devices; (2) astandardized approach, (3) intermittent banding for edu-cational purposes (5 days total). Target and passive net-ting included 1–3 technicians working most weekdaysbetween May 25–July 15 from sunrise to approximately11:30 AM to resight and target net colour-banded cat-birds between 2012 and 2018 at the first site only. Stan-dardized MAPS banding efforts occurred from 2011 to2018 at the first site and 2006–2018 at the second siteand involved 10 mist nets open 6 h a day for 7 sampleperiods during the breeding season [49]. Educationalbanding occurred only at the second site.Apparent annual survivorship was calculated usingRMark (v. 2.2.7 [50]) in R. Cormack-Jolly-Seber models[51, 52] were used, which included the apparent annualsurvivorship (ϕ) and detection probability (p) as modelparameters. Assumptions of Cormack-Jolly-Sebermodels are that (1) every bird has the same probabilityof being recaptured/resighted at the next samplingperiod; (2) every bird has the same probability of surviv-ing to the next sample period; (3) Colour-bands are notlost or missed, and; (4) sampling time is short (or in-stantaneous) relative to the interval in between samplingtimes. To assess the goodness-of-fit of our data to theassumptions of Cormack-Jolly-Seber models, we usedthe program RELEASE via RMark using the function‘release.gof’. Goodness-of-fit was assessed by examiningthe fit of the global model. Because we were comparingthe fit of multiple models with varying parameters, weMancuso et al. Movement Ecology (2021) 9:10 Page 4 of 16used the model with the highest number of parametersas the global model, which contained sex as a covariate.There was no evidence of a lack of fit of the globalmodel to Cormack-Jolly-Seber model assumptions (χ2 =27.35, df = 25, P-value = 0.34).Birds of all ages (except nestlings) were used in theanalyses. Sex was included as a covariate for both sur-vivorship and detection. To account for potential localdifferences between sites within each study area, site wasincluded as a covariate. Because the first encounter islikely to include young or transient birds who aremore likely to permanently leave the study areathrough death or immigration and thereby have alower apparent annual survivorship in this first yearafter being colour-banded, we included a time-since-marking covariate where the first encounter is sepa-rated from subsequent encounters [53, 54]. Multiplemodels that contained different combinations of co-variates were compared using an Akaike InformationCriteria (AIC) approach adjusted for small samplesizes (Table 1, Burnham and Anderson 2002). Weconsidered models with ΔAICc values of less than 2to have substantial support [55]. We also calculatedAICc weight and considered any model with a weightof greater than 0.90 as a clear top model [55]. For allanalyses, mean and standard error are reported unlessotherwise noted.ResultsIn British Columbia, the return rate of birds withgeolocators was 8 out of 39 (20.5%), and 7 geoloca-tors were retrieved. The return rate of catbirds withGPS tags was 6 out of 20 (30.0%), excluding one de-ceased catbird found in the same year of deployment.All 6 GPS tags were retrieved. We experienced poorperformance in the geolocator technology. One geo-locator had light data for only 2 months, but allother geolocators contained data for the full year.Light levels recorded on the geolocators were lowand inconsistent, making the determinations on sun-rises and sunsets spurious (an example of low-qualitygeolocator data can be found in additional file 1). Alllocation estimates were severely outside known over-wintering distributions (examples of erroneous loca-tion estimates can be found in additional file 1). AllGPS tags contained data but fewer than the adver-tised maximum number of 80 fixes.In Montana, the return rate of birds with geolocatorswas 10 out of 32 (31.3%), and 6 geolocators were re-trieved. The return rate of catbirds with GPS tags was18 out of 52 (34.6%), and 14 GPS tags were retrieved.All geolocators contained usable data, but 2 GPS tagsdid not contain usable data.Migration routesThe migration route identified from GPS tags showedcatbirds from Montana and British Columbia headingeast across the Rocky Mountain Range, then south to-wards overwintering locations in Mexico and Texas(Fig. 1). While navigating the Rocky Mountain Range,Gray Catbirds from British Columbia appear to havetraveled through lower elevation corridors; the elevationof points occurring within the Rocky MountainRange were 1939, 849, 1020, 917, 497, 392, 662, 886,and 1034 m whereas the mountainous peaks withinBritish Columbia, Washington, Idaho, and reachheights > 3000 m above sea level (Fig. 1). The fixesfor Montana Gray Catbirds occurred too far east ofthe Rocky Mountain Range to assess their specificpaths through the mountains.In 5 cases from Montana, we have at least part of thespring migration route. These birds followed the samegeneral routes in fall and spring (Fig. 2). Migration speedaveraged 113 km/day and we saw no difference betweenspring and fall (t = − 1.3, df = 10, P-value = 0.24, 95% CI:− 43.7, 12.2; Table 1). No spring migration data wasavailable from British Columbia catbirds due to GPS tagbattery exhaustion.Stopover sitesWe identified 20 fall stopover sites and one spring stop-over site from our two catbird populations combined(Fig. 3). None of the tagged Gray Catbirds stopped atthe same stopover site, and the closest sites were 24.7km apart. Stopover sites for British Columbia Gray Cat-birds were in Montana, Kansas, Oklahoma, Missouri,and Arkansas (Fig. 3). Stopover sites for Montana GrayCatbirds were in Kansas, Oklahoma, and Arkansas. Theamount of time spent at each stopover site ranged be-tween 1 to 16 days, but our estimate of stopover dur-ation is limited by the sampling interval of the GPS tagranging from 1 to 5 days during migration. From satelliteimagery, stopover habitat generally included patches oftrees or shrubby habitat, often within 500 m to water(satellite imagery of stopover sites can be found in add-itional file 2). The exception to the pattern of riparianhabitat use was one stopover in an urban environment.The elevation of stopover sites varied widely, from 74 to1060 m above sea level.Overwinter sitesGray Catbirds that bred in British Columbia and Mon-tana had overlapping overwintering areas in Texas andMexico. Gray Catbirds breeding in British Columbiaoverwintered in Texas, Tamaulipas, San Luis Potosi, Hi-dalgo, and Nuevo Leon, Mexico (Fig. 4 and Table 2).Gray Catbirds breeding in Montana overwintered inTexas, San Luis Potosi, Tamaulipas, Veracruz, Puebla,Mancuso et al. Movement Ecology (2021) 9:10 Page 5 of 16and Hidalgo. Gray Catbirds breeding in British Columbiatraveled an average of 4048 ± 193 km to overwinteringlocations, and Gray Catbirds breeding in Montanatraveled 3604 ± 76 km to overwintering locations.Overwintering location estimates from birds with geolo-cators were less precise than GPS tags but also encom-passed San Luis Potosi, Tamaulipas, and Veracruz(Fig. 5). One exception is a Gray Catbird with aTable 1 Movement summary of Gray Catbirds (Dumetella carolinensis) fitted with GPS tagsFall SpringTag ID Bird ID Sex Year Fix Loc. Depart Arrive Length(Days)Distance(km)Speed(km/day)Depart Arrive Length(Days)Distance(km)Speed(km/day)British Columbia42000YRGX M 2017 23 NLE Sep 6 Oct1236 3905 108 – – – – –42005YROX M 2017 53 TX Sep 10 Oct1232 3236 101 – – – – –48964BBRX M 2018 46 SLP Sep 10 Oct1636 4686 130 – – – – –48961BBXB M 2018 48 TAM Sep 12 Oct1432 4098 128 – – – – –48965BBYX M 2018 51 TAM, SLP,HIDSep 16 Oct2236 4171 116 – – – – –48963BBXD F 2018 28 TAM* Sep 6 Oct1640 4192 105 – – – – –Mean ± SE 35 ± 1.2 4048 ±193.5115 ±4.9Montana251 LLBkA F 2014 3 TAM – Dec 7 – 3235 – – – – – –262 DBkAR M 2014 4 TX – Dec 7 – 2746 – – – – – –245 RAWW M 2014 2 TAM – Jan 7 – 3507 – – – – – –40958LRYA M 2016 8 TAM, HID – Oct18– 3072 – – – – – –48126LRYA M 2017 38 TAM,HIDSep 14 Oct1935 3390 97 Apr 26 May3135 3501 10048120ODAS M 2017 41 TAM, VER,HIDSep 9 Oct1433 3358 102 May 3 May3128 3424 12248121OOAS F 2017 22 VER Sep 4 Oct2955 3911 71 – – – – –48123DOGA F 2017 36 TAM, HID Sep 9 Oct1435 3579 102 Apr 26 May2428 3764 13448124GOAS F 2017 40 TAM, VER Sep 19 Oct1930 3407 114 May 3 May3128 3677 13148131WWAS M 2017 36 TAM, SLP,VERSep 9 Oct1435 4032 115 – – – – –48133RLGA F 2017 37 TAM, PUE Sep 9 Oct1435 3401 97 May 3 – – – –48134ADBkW M 2017 37 VER, HID Sep 9 Oct 4 25 3760 150Mean ± SE** 35 ± 3.2 3604 ±76.2106 ±7.829 ± 2 3591 ± 78 122 ± 7.7*Last fix on October 16, assuming overwintering site but could potentially still be on migration**Mean (± Standard Error) but not including length or speed for units with less than 10 fixesSummary of GPS tags attached to Gray Catbirds in the South Okanagan Valley, British Columbia, Canada, and in the Bitterroot River Valley, Montana, USA with anemphasis on migration. Year is year GPS tag deployed. The fall depart date represents the last fix at the breeding site and the arrival date represents the first fixat the overwintering site. The spring depart date represents the last fix at the overwintering site and the arrival date represents the first fix back at the breedingsite. Locations (Loc.) are abbreviated as Nuevo Leon (NLE), San Luis Potosi (SLP), Tamaulipas (TAM), Veracruz (VER), Hidalgo (HID), Puebla (PUE), and Texas (TX).Dashes indicate missing data: fall depart date is unclear from three Bitterroot River Valley catbirds due to first fixes occurring mid-migration; lack of springmigration data is due to premature battery exhaustionMancuso et al. Movement Ecology (2021) 9:10 Page 6 of 16geolocator whose overwintering estimate was centeredover Oaxaca, Mexico, and the Pacific Ocean - thelongitude of this estimate is in accordance with allother Gray Catbird overwintering estimates but thelatitude appears suspect (Fig. 5).From GPS tags, we found that several Gray Catbirdsfrom Montana and British Columbia populations usedmore than one overwintering location, with up to fourdistinct locations documented (Table 2). Each subse-quent overwintering location was farther south than theFig. 1 Gray Catbird (Dumetella carolinensis) fall migration route. Southward migration path from GPS tags retrieved from Gray Catbirds breedingin the South Okanagan Valley, British Columbia, Canada, and in the Bitterroot River Valley, Montana, USA. Gray tracks are from GPS tags retrievedfrom catbirds in the Bitterroot River Valley (n = 12) and black tracks are from GPS tags retrieved from catbirds in the South Okanagan Valley (n = 6).World Terrain Base Map provided by ESRI, USGS, and NOAA within ArcMap 10.7.1. Map created in ArcMap 10.7.1 (ESRI 2019) using the GCS WGS 1984coordinate system. The elevation map was created in ArcMap 10.7.1 using the 30 arc-second digital elevation model of North America (ESRI 2019)Fig. 2 Comparing north vs. south migration routes for Gray Catbirds (Dumetella carolinensis). A comparison of southward (black) and northwardmigration (gray) GPS tracks from 5 different Gray Catbirds marked in their breeding site in the Bitterroot River Valley, Montana, USA. All birds wereheading north by May 10, except for catbird with GPS 41820, who headed north by May 3. Map created in ArcMap 10.7.1 using the GCS WGS1984 coordinate system (ESRI 2019)Mancuso et al. Movement Ecology (2021) 9:10 Page 7 of 16previous one, except one Gray Catbird who moved slightlyfarther north for his second overwintering location, thensouth for subsequent locations. Distance between over-wintering locations ranged from 5 to 353 km. The lengthof stay at any one overwintering location ranged from 17to 169 days. During winter, Gray Catbirds occupied nat-ural areas with dense vegetative cover, often in associationwith edges or riparian habitats, at elevations of 9–678mabove sea level (satellite imagery of overwintering loca-tions can be found in additional file 2).Multiple years of trackingSome birds tracked over multiple years in Montana showedfidelity to overwintering locations (Fig. 6). One female GrayCatbird had two similar overwintering locations based onone GPS tag and one geolocator. This individual also hadFig. 3 Migration stopover sites identified for Gray Catbirds (Dumetella carolinensis). Stopover sites identified using GPS tags. Crosses representbirds tagged in the South Okanagan Valley, British Columbia, Canada, and exes represent birds tagged in the Bitterroot River Valley, Montana,USA. Stars represent study site locations. All sites are from fall migration, except for the asterisk in Texas, which was a spring stopover site for aGray Catbird that bred in the Bitterroot River Valley. Points are scaled relative to the amount of time spent at a site and range between 1 and 16days. Gray Catbird range map provided by IUCN (2016). Map created in ArcMap 10.7.1 using the GCS WGS 1984 coordinate system (ESRI 2019)Mancuso et al. Movement Ecology (2021) 9:10 Page 8 of 16the potentially unreliable geolocator where latitude estimatesappeared unlikely. One male Gray Catbird had likely differ-ent overwintering estimates, with one geolocator showingMexico and one GPS tag showing Texas. Another male GrayCatbird showed strong overwintering fidelity over two yearsbased on data from two GPS tags.Fig. 4 Gray Catbird (Dumetella carolinensis) overwintering sites. Overwintering points were determined from GPS tags retrieved from Gray Catbirdsbreeding in the South Okanagan Valley, British Columbia, Canada (red squares), and the Bitterroot River Valley, Montana, USA (blue circles). The size ofthe symbol represents how long the bird stayed at the site, ranging from 4 to 169 days. Most birds had more than one overwintering site. GrayCatbird range map provided by IUCN (2016). Map created in ArcMap 10.7.1 (ESRI 2019) using the GCS WGS 1984 coordinate systemMancuso et al. Movement Ecology (2021) 9:10 Page 9 of 16Migratory connectivityWe observed weak migratory connectivity for BritishColumbia and Montana catbird populations; there wasno significant correlation between the distances of birdsin the breeding grounds and the distances of birds in theoverwintering grounds (rM = 0.013, P-value = 0.41). Add-itionally, the average pairwise distances in the overwin-tering grounds (British Columbia: 347.2 ± 68.3 km, n =15, Montana: 255.8 ± 34.7 km, n = 66) were greater thanthe average pairwise distances in the breeding grounds(British Columbia: 0.74 ± 0.11 km, n = 15, Montana:0.02 ± 0.002 km, n = 66), highlighting the degree ofspread between different phases of the annual cycle.Apparent annual survivorshipThe top model for apparent annual survivorship ofMontana Gray Catbirds included sex and site and had aweight of 93% and no other model had an ΔAICc valueof < 2, suggesting that this model had the greatest sup-port (Table 3). Therefore, parameter estimates for thismodel alone are reported. The apparent annual survivor-ship was greater for males (ϕ = 0.43 ± 0.04) than females(ϕ = 0.34 ± 0.05, Table 4).The top model for apparent annual survivorship of Brit-ish Columba Gray Catbirds included sex and had a weightof 98% and no other model had an ΔAICc value of < 2.Therefore, parameter estimates for this model alone arereported. The top model for apparent annual survivorshipin British Columbia included sex as a covariate for bothsurvivorship and detection probability (Table 1). Maleshad greater detection probability (p = 0.72 ± 0.07) than fe-males (p = 0.25 ± 0.07) and birds of unknown sex (p =0.35) but males and females had similar survivorship (ϕ =0.64 ± 0.05 and 0.61 ± 0.06, respectively, Table 4).DiscussionThis study represents the first published information onmigration, overwintering locations, and survival rates ofwestern populations of Gray Catbirds. As such, it con-tributes to our collective knowledge of the species andprovides baseline information against which to monitorfuture population change.Our findings support past suspicions that western cat-birds follow the Central Flyway, despite breeding loca-tions within the Pacific Flyway. The Rocky Mountainsdid not appear to be a barrier during fall and springTable 2 Summary of Gray Catbird (Dumetella carolinensis) overwintering locations identified using GPS tagsWinter Location 1 Winter Location 2 Winter Location 3 Winter Location 4Tag ID Dates State Days Dates State Days KM Dates State Days KM Dates State Days KMBritish Columbia42000 Oct 12-Nov 1 NLE 2042005 Oct 12-Mar 9 TX 15848964 Oct 16-Mar 27 SLP 162 Mar 31-Apr 10 SLP 10 10948961 Oct 14-Apr 2 TAM 16948965 Oct 22-Oct 26 TAM 4 Dec 1-Feb 1 TAM 62 32 Mar 1-Mar 17 SLP 16 178 Mar 19-Apr 20 HID 32 6748963 Oct 16 TAMBitterroot River Valley251 Dec 7-Jan 7 TAM 30262 Dec 7-Feb 7 TX 62245 Jan 7 TAM40958 Oct 18-Jan 5 TAM 79 Feb 4 TAM 19 Mar 1 HID 27848126+ Nov 1-Nov 21 TAM 20 Dec 1-Feb 19 TAM 80 5 Mar 15-Apr 26 HID 42 27548120 Oct 14-Nov 11 TAM 28 Dec 1-Feb 19 TAM 81 114 Mar 8-Apr 19 VER 41 234 Apr 26-May 3 VER 7 848121 Oct 29-Dec 21 VER 53 Dec 31 VER 648123 Oct 14-Mar 1 TAM 138 Mar 15-Apr 26 HID 42 35348124 Oct 19-Mar 1 TAM 133 Mar 8-May 3 VER 56 31348131 Oct 14-Jan 20 TAM 98 Feb 19-Mar 8 SLP 17 168 Mar 22-Apr 26 VER 35 7948133 Oct 14-Feb 19 TAM 128 Mar 29-May 3 PUE 63 27548134 Oct 14-Mar 29 VER 176 Apr 5-May 3 HID 28 119+This bird moved around in Tamaulipas between Oct 19 and Nov 1Details of overwintering sites obtained from GPS tags placed on Gray Catbirds in the South Okanagan Valley, British Columbia, Canada, and the Bitterroot RiverValley, Montana, USA. Abbreviations include minimum length of stay (Days), the distance between current and previous overwintering site (KM). States areabbreviated as Nuevo Leon (NLE), San Luis Potosi (SLP), Tamaulipas (TAM), Veracruz (VER), Hidalgo (HID), Puebla (PUE), and Texas (TX)Mancuso et al. Movement Ecology (2021) 9:10 Page 10 of 16migration. GPS data from British Columbia catbirds fur-ther highlight that low-elevation corridors are likely usedto cross the mountainous landscape.The migration route for western Gray Catbirds mayreflect the evolution of migration in these populationsduring historical range expansion, similar to Veeries inBritish Columbia [22]. As is postulated for Veeries, GrayCatbirds likely originated in eastern North America andthen slowly expanded their range northward and thenwestward as the continental glaciers receded [22]. Theabsence of this species in most of the Pacific Northwest,such as coastal Washington, Oregon, and California, isconsistent with this hypothesis. The relicts of historicalrange expansions are recapitulated in migration and canFig. 5 Overwintering locations of Gray Catbirds (Dumetella carolinensis) breeding in the Bitterroot River Valley, Montana, USA. Each polygonrepresents the 50% Kernel Density Estimates from locations obtained from archival light-level geolocators between November 15 – March 1 for1 year from 2014 to 2018. Gray Catbird range map provided by IUCN (2016). Map created in ArcMap 10.7.1 (ESRI 2019) using the GCSWGS 1984 coordinate systemFig. 6 Repeat tracking of 3 separate Gray Catbirds (Dumetella carolinensis) in different years. Tracking devices were deployed in the BitterrootRiver Valley, Montana, USA. The year that the track was recorded is shown. Map created in ArcMap 10.7.1 (ESRI 2019) using the GCS WGS 1984coordinate system. Geolocator abbreviated as GeoMancuso et al. Movement Ecology (2021) 9:10 Page 11 of 16be observed in other species whose breeding and over-wintering grounds are continents apart, such as North-ern Wheatear (Oenanthe oenanthe [56]), Bar-tailedGodwit (Limosa lapponica [57]), and Blackpoll Warbler(Setophaga striata [58]). In British Columbia, ancestralroutes similar to what we have found in the westernGray Catbird have also been observed in Swainson’sThrushes [20, 59], but our study is the first to documentthis phenomenon in the Mimidae family.Ancestral relicts of range expansion may also work inconjunction with ecological limitations to explain whythe migratory routes we documented are indirect andfarther east than we expected [60]. Gray Catbirds oc-cupy riparian habitat and shrubby edges throughouttheir range [40, 61]. Riparian habitats identified at ourstopover locations suggest these cover types may be ofparticular importance during migration by providingboth food and water, as has been documented for otherbird species [4, 62, 63]. Indeed, fall stopover sites appearconcentrated after migrating along the edge of the semi-arid great plains and reaching the temperate forest eco-region, replete with wetlands, forests, and a temperateclimate [64]. Therefore, catbirds taking the easterly routemay have experienced an evolutionary advantage byspending more time in higher quality stopover habitateven as their range expanded westward.In addition to confirming that catbirds use riparianand edge habitats for stopovers, we also found stopoverlocations dispersed on the landscape and not used re-peatedly or by the same birds, though we acknowledgewe have a relatively small sample size and this topicmerits further study. Dispersed and abundant stopoversites pose a challenge for conservation as the persistenceof many small riparian areas along the migration routemay be necessary to support current Gray Catbird popu-lations. Alternatively, perhaps the loss of any one patchof habitat is less consequential as long as a certainthreshold of suitable habitat is maintained at the land-scape scale. We suggest additional study into importantfeatures of stopover locations and to what extent cat-birds are plastic in their use of such sites. Conserving anetwork of riparian habitats across the landscape is avaluable conservation approach for not just Gray Cat-birds, but other wildlife, as it allows for landscape-levelconnectivity and the retention of movement corridors.Birds from both of our study populations overwinteredalong the Gulf Coast of Texas south into northeasternMexico, with the highest concentration in the Tamau-lipas region. These sites do not overlap with knownoverwintering locations of Midwestern and mid-Atlanticcatbirds [13] and thus represent a major advance in ourunderstanding of the precise geographic linkages be-tween breeding and overwintering catbird populations.We also saw some evidence of overwintering site fidelity,though potentially erroneous geolocator data limits ourability to confirm this behaviour across many individ-uals. In any case, repeated tracking of individual song-birds over multiple years is rare and, even if limited bysample size and technology, represents a major accom-plishment of our study.Our study is the first to document Gray Catbird’s useof multiple overwintering locations; we found individualsused multiple overwintering locations and moved farthersouth as the winter progressed into spring. The use ofmore than one overwintering location has been observedin a few other neotropical migrants (e.g. ProthonotaryWarblers (Protonotaria citrea), Veeries, and Swainson’sThrushes [22, 65–67]). Future tracking studies onTable 3 Gray Catbird (Dumetella carolinesis) apparent annualsurvivorship model comparisonModel Parameters AICc ΔAIC Weight DevianceMontana (n = 741)ϕ (sex) p (site) 5 496.4 0.00 0.93 159.9ϕ (sex) p (.) 4 503.0 6.56 0.04 130.5ϕ (site) p (sex) 5 503.7 7.27 0.02 167.2ϕ (sex) p (sex) 6 506.8 10.36 0.01 130.2ϕ (.) p (sex) 4 511.3 14.91 0.00 138.9ϕ (TSM) p (sex) 5 513.3 16.94 0.00 138.9ϕ (TSM) p (.) 3 552.4 56.00 0.00 65.2ϕ (site) p (.) 3 596.4 100.00 0.00 124.3ϕ (.) p (site) 3 596.5 100.14 0.00 124.4ϕ (site) p (site) 4 598.2 101.76 0.00 124.0ϕ (TSM) p (site) 4 598.6 102.17 0.00 124.4ϕ (.) p (.) 2 600.7 104.20 0.00 115.4British Columbia (n = 537)ϕ (sex) p (sex) 6 709.2 0.00 0.98 119.2ϕ (sex) p (.) 4 718.1 8.91 0.01 132.1ϕ (sex) p (site) 5 719.4 10.16 0.01 164.3ϕ (site) p (sex) 5 724.0 14.82 0.00 169.0ϕ (.) p (sex) 4 724.2 15.00 0.00 138.2ϕ (TSM) p (sex) 5 726.1 16.91 0.00 138.1ϕ (TSM) p (.) 3 813.4 104.24 0.00 51.1ϕ (TSM) p (site) 4 815.4 106.22 0.00 76.4ϕ (.) p (.) 2 836.7 127.48 0.00 76.4ϕ (site) p (.) 3 838.5 129.34 0.00 101.6ϕ (.) p (site) 3 838.6 129.45 0.00 101.7ϕ (site) p (site) 4 839.7 130.48 0.00 100.7Models for the apparent annual survivorship of Gray Catbirds in the SouthOkanagan Valley, British Columbia, Canada, and the Bitterroot River Valley,Montana, USA. Cormack-Jolly-Seber models were used, which include annualsurvivorship (ϕ) and detection probability (p). TSM is a time-since-markingapproach whereby the first encounter is separated from separate encountersto factor in young and transient individuals. Intercept only models aredesignated by (.)Mancuso et al. Movement Ecology (2021) 9:10 Page 12 of 16additional species would help us understand if this behav-iour is rare or common amongst neotropical migrants. Themechanisms driving overwinter movement warrants furtherresearch; plausible explanations may be that birds follow ashift in seasonal food resources or avoid weather events. Abetter understanding of overwintering habitat use and howit may vary by age and sex is a priority for future Gray Cat-bird research [40]. The ability of individuals to exhibit someplasticity in overwintering locations, suggests a life-historystrategy adapted to landscape change. From a conservationperspective, the potential plasticity of overwintering site usemay be an adaptive strategy that will bode well for the fu-ture of catbird populations to persist as habitats shift due toanthropogenic or natural causes.That Gray Catbirds use multiple overwintering loca-tions and vary in their degree of overwintering locationfidelity question important assumptions of overwinteringmonitoring programs, such as Monitoreo de Sobrevi-viencia Invernal (MoSI), which uses standardized mist-netting efforts during the overwintering period to assessoverwintering survivorship [68]. The MoSI protocol in-volves 5 monthly overwinter mist-netting pulses fromNovember to the end of March where each pulse occursover 2–3 days [69]. The Gray Catbird was one targetspecies for the MoSI program but their overwinteringsurvivorship estimates will likely be underestimatedgiven their overwinter movements [69]. A better under-standing of songbird overwintering movement and sitefidelity in other species is crucial to assessing the accur-acy of vital rate metrics derived from MoSI data.Migratory connectivityWe found weak migratory connectivity for the two GrayCatbird populations we examined, with Montana andBritish Columbia Gray Catbirds overwintering in similarareas across northeastern Mexico. Birds that bred closeto one another dispersed up to 1000 km apart during theoverwintering period. Weak migratory connectivity maybe advantageous for the persistence of western catbirdpopulations because individuals are dispersed across alarge geographic region during the overwintering periodare unlikely to be affected by local threats.One challenge in comparing migratory connectivitybetween studies is the scale in which it is examined. Ifwe consider both breeding sites from British Columbiaand Montana as one population, and the span of Texasto Veracruz as one overwintering population, it wouldbe perceived as strong migratory connectivity. Ryderet al. [13] reported strong migratory connectivity foreastern and central populations of Gray Catbirds. Re-gardless, the results of our study and previous studies onmigration patterns of Gray Catbirds result in a compre-hensive picture of population connectivity across theirrange. Gray Catbirds breeding in the west overwinter inTexas and northeastern Mexico [this study and 94]. Cat-birds breeding in the mid-west overwinter in CentralAmerica [13], Catbirds breeding near the Great Lakesoverwinter in Guatemala [70] and Catbirds breeding inthe Atlantic overwinter in Cuba and the CaribbeanIslands [13].Apparent annual survivorshipEstablishing demographic rates for species, such as ap-parent annual survivorship, are important for identifyingpopulations at risk of decline and informing conserva-tion efforts [11, 71]. The estimates for Gray Catbirds inBritish Columbia (0.61 ± 0.06 female, 0.64 ± 0.05 males)exceed reported adult average survivorship values in theTable 4 Gray Catbird (Dumetella carolinensis) apparent annual survivorship model parameter estimatesModel Parameter Group Estimate Standard ErrorMontanaϕ (sex) p (site) ϕ Female 0.34 0.05ϕ (sex) p (site) ϕ Male 0.43 0.04ϕ (sex) p (site) ϕ Unknown 0.06 0.01ϕ (sex) p (site) p MPG Ranch 0.77 0.07ϕ (sex) p (site) p Other 0.34 0.10British Columbiaϕ (sex) p (sex) ϕ Female 0.61 0.06ϕ (sex) p (sex) ϕ Male 0.64 0.05ϕ (sex) p (sex) ϕ Unknown 0.20 0.20ϕ (sex) p (sex) p Female 0.25 0.07ϕ (sex) p (sex) p Male 0.72 0.07ϕ (sex) p (sex) p Unknown 0.35 0.13Parameter estimates for the top apparent annual survivorship models for Gray Catbirds in British Columbia and Montana. Cormack-Jolly-Seber models were used,which include annual survivorship (ϕ) and detection probability (p)Mancuso et al. Movement Ecology (2021) 9:10 Page 13 of 16Northern Rockies bird conservation region (which spansboth study areas) of 0.54 ± 0.02 between 1992 and 2006[72]. For comparison, apparent annual adult survivorshipfor other common songbirds in the Northern Rockiesbird conservation region ranges between 0.50–0.59 [72].Why the apparent annual survivorship estimates forMontana Gray Catbirds (0.34 ± 0.05 females, 0.41 ± 0.04males) are lower is unclear. However, when averagedacross both sites, survivorship values match those of thegeneral Northern Rockies conservation region, so per-haps the range of values we are documenting at localsites are in line with regional trends. Because birds fromboth study areas traveled along similar routes and over-wintered in similar locations, differences are likely attrib-uted to breeding locations. Breeding site fidelity incatbirds is linked with reproductive success, where birdsthat successfully reproduce are more likely to return tothe same territory, therefore probing deeper into nestsuccess in Montana might provide more insight into ap-parent annual survivorship trends [73]. Additionally, thedegree of urbanization between the two sites may berelevant, as eastern catbirds exhibit lower survival inrural than urban areas (suspected due to food availabil-ity), and our Montana site was more rural than our Brit-ish Columbia site [74]. Both study areas had resightingefforts, which when combined with recapture methods,improves apparent annual survivorship estimates [75].However, overall resighting effort in Montana wasslightly lower than in British Columbia, and therefore,could have skewed the results. As technology advances,we are hopeful that one day we will be better able tounderstand whether birds that do not return to the sitein subsequent years are dispersing to new areas, remainundetected, or are dying.ConclusionsOur study represents the first description of full annualcycle movements of western populations of Gray Cat-birds, revealing that catbirds breeding in two disparatepopulations followed similar migratory routes eastwardacross the Rocky Mountain Range then southward to-wards overwintering locations in northeastern Mexicoand Texas, following a putative ancestral route. Duringthe non-breeding season, individuals from both breedingpopulations spread out across overlapping geographicareas, a case of weak migratory connectivity. Unexpect-edly, Gray Catbirds used multiple overwintering loca-tions which suggests some plasticity in movement thatmay help catbirds remain adaptable if landscapeschange. Like many previous catbird studies, our researchfound that western catbird populations use riparian andshrubby plant communities for breeding, stopover sites,and overwintering sites.From a conservation perspective, the detail we nowhave on the full annual cycle of Gray Catbirds may helpin ensuring the species remains a common species onthe landscape well into the future. Preserving key areasof suitable habitat in the central and southern portionsof Tamaulipas would benefit both Montana and BritishColumbia Gray Catbirds because our study identifiedTamaulipas as a key overwintering area. Additionally,with the predicted effects of climate change impactingthe persistance and quality of riparian habitats, pro-actively protecting and monitoring riparian areas alongtheir migration route and stopover areas may allow us todetect changes early [76, 77]. Moreover, should a popu-lation decline occur in the future, the baseline informa-tion on the survivorship and migratory connectivity ofthese populations we describe in detail will be valuablefor conservation efforts [78].AbbreviationsAIC: Akaike’s Information Criteria; GPS: Global Positioning System;MoSI: Monitoreo de Sobreviviencia Invernal; rM: Mantel’s correlation;USA: United States of AmericaSupplementary InformationThe online version contains supplementary material available at https://doi.org/10.1186/s40462-021-00249-7.Additional file 1. Low-quality geolocator results. Additional file 1 showsan example of low-quality archival light-level geolocator data and the as-sociated geographic assignment locations.Additional file 2 Aerial imagery of stopover and overwintering sites.Shows satellite imagery of stopover and overwintering site locations asdetermined from GPS tags attached to Gray Catbirds (Dumetellacarolinensis).AcknowledgementsWe thank all the skilled field technicians and volunteers who deployed andretrieved tracking devices as well as resighting and recapturing colour-banded catbirds, including T. Forrester, A. Huang, K. Owen, M. Bieber, M.Aubertin-Young, S. Hudson, K. Hick, A.M. Bezener, H. Hall, A. Gonzalez, S. Eng-lish, S. Fuller, M. Ruggles, A. Spidal, C. Taft, L. Fried, and A. Meyer. T. Rodriguezhelped prepare data files for M. Blake who modelled the coding in RMark foranalysis of the survivorship of Montana Catbirds. M. Blake and L. Fried alsosubstantially increased our sample size during the 2018 field effort. We thankthe En’owkin Centre and the Penticton Indian Band for their collaborative ef-forts with this research. J. Pither, J. Alexander, and A. Ford suggested im-provements to a draft of this manuscript. We thank K. Hobson and S. VanWilgenburg for initiating the study of Gray Catbirds in British Columbia andfor technical help with fitting geolocators.Authors’ contributionsCAB, MAF, KEH, and KRS conceived the project idea and contributedsubstantial materials, resources, and funding. Field data were collected byMAF, KAM, and MBL. KAM performed data analyses, created all figures andtables, and wrote the manuscript with guidance from KEH, CAB, MAF, andKRS. All authors read and approved the final manuscript.FundingFunding was provided by Environment and Climate Change Canada, theUniversity of British Columbia Okanagan, Natural Sciences and EngineeringResearch Council of Canada for the study design, data collection in Canada,analysis, interpretation, and writing of the manuscript. Funding was providedby Montana State University, and MPG Ranch for the study design, dataMancuso et al. Movement Ecology (2021) 9:10 Page 14 of 16collection in the USA, survivorship analysis for catbirds in the USA, andeditorial advice.Availability of data and materialsThe datasets supporting the conclusions of this article will be available in theOpen Science Framework repository.Ethics approval and consent to participateAll research on birds was approved by the University of British ColumbiaOkanagan Animal Care Committee (application number A16–0079) and theUniversity of Montana Institutional Animal Care and Use Committee (022–17). Federal bird banding permits (10761 L,10761Q, 10761R, 23206) andMontana Fish, Wildlife, and Parks permits were acquired for bird bandingactivities in Montana.Consent for publicationNot applicable.Competing interestsThe authors declare that they have no competing interests.Author details1Department of Biology, University of British Columbia Okanagan, Kelowna,British Columbia, Canada. 2Division of Biological Sciences, University ofMontana, Missoula, MT, USA. 3Science and Technology Branch, Environmentand Climate Change Canada, Delta, British Columbia, Canada. 4Oliver,Canada. 5MPG Ranch, Florence, MT, USA.Received: 16 November 2020 Accepted: 24 February 2021References1. Rosenberg KV, Dokter AM, Blancher PJ, Sauer JR, Smith AC, Smith PA, et al.Decline of the North American avifauna. Science (80- ). 2019;366:120–4.2. Sauer JR, Pardieck KL, Ziolkowski DJ, Smith AC, Hudson MR, Rodriguez V,et al. The first 50 years of the north American breeding bird survey. Condor.2017;119:576–93.3. 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Vancouver : University of British Columbia Library
BioMed Central
Attribution 4.0 International (CC BY 4.0)
Faculty
Dumetella carolinensis
Full annual cycle
Migration
Migratory connectivity
GPS tracking
Migration ecology of western gray catbirds
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