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UBC Theses and Dissertations
The timing of breeding in double-crested cormorants (phalacrocorax auritus albociliatus) : its effects on clutch size, nestling growth, diet and survival Sullivan, Terrance Michael
Abstract
I examined the effects of a delayed time of breeding on clutch size, nestling growth and diet of Double-crested Cormorants (Phalacrocorax auritus albociliatus) at three colonies, Five Finger Island, Mandarte Island and the Fraser River, during the 1993 and 1994 breeding seasons. The effect of population changes was also monitored at these colonies and 4 additional colonies, Crofton, Chain Island, Christie Islet and Hudson Rocks, all situated within the Strait of Georgia As the breeding season progressed, asymptotic mass and condition index of the nestlings declined. In general, nestlings produced early in the season were heavier, had a slower growth rate and required more time to achieve their final mass than those produced later in the season. The last birds to breed were on the Fraser River (1993) where successful egg laying occurred approximately 3 months after the first colony (Five Finger Island) bred. The patterns of growth of the structural components differed at this colony from all others. The asymptotic length of both the culmen and tarsus, and the overall size of the nestlings increased as the season progressed. These parameters were also larger than at all other colonies. Nestling cormorants on Five Finger Island were fed mainly- Pacific Sandlance, nestlings on Mandarte Island were fed mainly blennies and those on the Fraser River were fed mainly Pacific Staghorn Sculpin and Shiner Perch. Colony differences probably reflect colony locations in the Strait of Georgia but may be influenced by the time of breeding. The quantity or quality of food delivered to the nestlings did not differ among colonies, except for the amount of lipids. Differences in nestling growth could not be explained by differences in the diet. To determine the effect of the timing of breeding on the changes in cormorant numbers, I modeled the dynamics of the population. Both the predicted and observed changes in the breeding population followed the same trend: at colonies where breeding occurred early in the season, there was an overall increase in the breeding populations while those that bred later in the season showed a decline. This trend was hypothesized to result from poor survival of the nestlings resulting in low recruitment into the breeding population.
Item Metadata
Title |
The timing of breeding in double-crested cormorants (phalacrocorax auritus albociliatus) : its effects on clutch size, nestling growth, diet and survival
|
Creator | |
Publisher |
University of British Columbia
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Date Issued |
1998
|
Description |
I examined the effects of a delayed time of breeding on
clutch size, nestling growth and diet of Double-crested
Cormorants (Phalacrocorax auritus albociliatus) at three
colonies, Five Finger Island, Mandarte Island and the Fraser
River, during the 1993 and 1994 breeding seasons. The effect of
population changes was also monitored at these colonies and 4
additional colonies, Crofton, Chain Island, Christie Islet and
Hudson Rocks, all situated within the Strait of Georgia
As the breeding season progressed, asymptotic mass and
condition index of the nestlings declined. In general, nestlings
produced early in the season were heavier, had a slower growth
rate and required more time to achieve their final mass than
those produced later in the season.
The last birds to breed were on the Fraser River (1993)
where successful egg laying occurred approximately 3 months
after the first colony (Five Finger Island) bred. The patterns
of growth of the structural components differed at this colony
from all others. The asymptotic length of both the culmen and
tarsus, and the overall size of the nestlings increased as the
season progressed. These parameters were also larger than at all
other colonies.
Nestling cormorants on Five Finger Island were fed mainly-
Pacific Sandlance, nestlings on Mandarte Island were fed mainly
blennies and those on the Fraser River were fed mainly Pacific
Staghorn Sculpin and Shiner Perch. Colony differences probably
reflect colony locations in the Strait of Georgia but may be
influenced by the time of breeding.
The quantity or quality of food delivered to the nestlings
did not differ among colonies, except for the amount of lipids.
Differences in nestling growth could not be explained by
differences in the diet.
To determine the effect of the timing of breeding on the
changes in cormorant numbers, I modeled the dynamics of the
population. Both the predicted and observed changes in the
breeding population followed the same trend: at colonies where
breeding occurred early in the season, there was an overall
increase in the breeding populations while those that bred later
in the season showed a decline. This trend was hypothesized to
result from poor survival of the nestlings resulting in low
recruitment into the breeding population.
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Extent |
5546890 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-05-19
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0088450
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1998-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.