Age‐dependent breeding dispersal and adult survival within a metapopulation ofCommonTernsSterna hirundo

Abstract

Dispersal is increasingly recognized as a process of fundamental importance in population dynamics and other aspects of biology. Concurrently, interest in age‐dependent effects on survival, including actuarial senescence, has increased, especially in studies of long‐lived seabirds. Nevertheless, datasets necessary for studying dispersal and age‐dependent effects are few, as these require simultaneous data collection at two or more sites over many years. We conducted a 22‐year capture‐mark‐recapture study of Common Terns Sterna hirundo at three breeding colonies 10–26 km apart in Buzzards Bay, Massachusetts, USA. All birds in the study were of known age (range 2–28 years, median 7 years, n = 3290) and 77% were of known sex. Estimates of adult recapture, survival and breeding dispersal rates were obtained for all age‐classes from 2 to 20 years. The model that acquired 100% of the QAICc (Akaike's Information Criterion adjusted for small sample size and overdispersion) weight in our analysis included age‐specificity in all parameters but no relationship with sex. Our study may be the first to demonstrate age‐specificity in recapture, survival and breeding dispersal rates simultaneously, using a single model. Annual rates of breeding dispersal ranged from <0.01 to 0.27, with a population‐weighted mean of 0.065; they decreased with increasing distance between colony sites and, unexpectedly, increased with age. Breeding dispersal did not increase consistently after years with predation on adults or after an attempt to displace birds from an oiled site. Survival rates did not vary among sites or years. Annual adult survival increased from 0.80 in 2‐year‐old birds to a maximum of approximately 0.88 around age 8 years and then declined to 0.76 at age 20 years, yielding strong evidence for actuarial senescence. The peak annual survival rate of 0.88 is at the low end of other estimates for Common Tern and in the lower part of the range recorded for other terns, but total numbers in the three colonies increased seven‐fold during the study. This was part of a slower increase in the regional population, with net immigration into the study colonies. Our results demonstrate the biological significance of breeding dispersal in local population dynamics and age‐related effects on survival and dispersal from a metapopulation of a long‐lived seabird.

Adult Survival and Breeding Dispersal of Common Terns (Sterna hirundo) in a Declining Population

“…The variance inflation factor (ĉ) was small at 1.12, suggesting a good fit of the most general model with the data (ĉ = 1.0 indicates a perfect fit), and was used in model selection and estimation of the uncertainty around parameter estimates (Spendelow et al 2008;Breton et al 2014). Model selection was therefore based on QAIC c (AIC corrected for overdispersion and small sample size; Burnham and Anderson 2002).…”

“…This number is within the range of previous adult survival estimates for Common Terns based on capture-recapture modeling. Most published estimates fall between approximately 0.88 and 0.92 with lower numbers for young adults or very old birds (Nisbet and Cam 2002;Becker 2012, 2015;Zhang et al 2015), and Breton et al (2014) found peak survival of 0.88 in middle-aged adults. However, our estimate for the less productive sites was very low, at 0.70 to 0.72 depending on the model, but with high uncertainty around these estimates.…”

“…A secondary objective was to document the recent population decline and provide estimates of productivity. If the population is rapidly declining and breeding failure common, then we predict that emigration should be frequent, which should result in relatively low apparent survival and relatively high movement probability compared to previously published estimates from more stable locations (Nisbet and Cam 2002;Becker 2012, 2015;Breton et al 2014).…”

“…data). A decrease in the number of adults could result from increased mortality, increased emigration, and/or decreased recruitment (Szostek and Becker 2012;Breton et al 2014). …”

“…Although this species is well-studied, few previous studies of Common Terns have simultaneously examined survival and dispersal across multiple sites using capture-mark-recapture methodology (Nisbet and Cam 2002;Breton et al 2014). A secondary objective was to document the recent population decline and provide estimates of productivity.…”