Are there trade-offs between pre- and post-fledging survival in black brent geese?
1. The growth period is an important determinant of fitness later in life through its effects on first-year survival and future reproduction. Choices by adult females about where to rear their offspring strongly affect growth rates and offspring fitness in geese. 2. Individual female black brent (Branta bernicla nigricans) tend to raise their broods in the same areas each year, and these areas are consistently ranked with respect to growth rates of goslings. Therefore, some females consistently rear their broods on areas resulting in lower post-fledging fitness. 3. We explore the potential that growth rates of offspring (and associated fitness consequences) are traded off against other vital rates influencing fitness of either adult females or goslings. Growth of goslings primarily influences fitness after fledging, so one hypothesis is that survival before fledging, which is influenced by predation, is traded off against growth rates and post-fledging survival. 4. We estimated pre-fledging and post-fledging survival for goslings reared on areas used by broods from the Tutakoke River black brent colony. We examined recaptures, recoveries by hunters and resightings of brent marked as goslings with webtags and standard leg rings. These data were analyzed using capture-mark-recapture models in program mark to derive separate estimates of pre- and post-fledging survival for 18 cohorts (1987-2004) of black brent goslings across seven brood rearing areas (BRAs). 5. Estimates of pre-fledging survival probability varied from 0·00 ± 0·00 (mean ± 95% confidence interval) to 0·92 ± 0·1; and estimates of post-fledging survival probability varied from 0·00 ± 0·00 to 1·00 ± 0·08. Substantial variation existed both among BRAs and years but post-fledging survival declined substantially during the study. 6. Pre- and post-fledging survival were positively correlated, exhibiting a quadratic relationship (ß(post-fledging survival)  = 1·00 (±0·47)x-0·83 (±0·480)x(2) , where x = pre-fledging survival). Therefore, we did not find a trade-off between pre- and post-fledging survival in black brent goslings across BRAs, suggesting that factors other than foraging conditions and predation on goslings must influence selection of BRAs.
Department of Natural Resources and Environmental Science, University of Nevada Reno, Reno, NV 89512, USA. chris_nicolai@fws.gov
Christopher A
CA
Nicolai
James S
JS
Sedinger
D017677:Age Distribution; D000413:Alaska; D000818:Animals; D005260:Female; D005777:Geese / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D056084:Genetic Fitness; D016014:Linear Models; D008136:Longevity; D008297:Male; D008954:Models, Biological; D011157:Population Dynamics; D012098:Reproduction; D012621:Seasons