The Breeding Ecology and Behavioral Endocrinology of Ruddy Turnstones (Arenaria Interpres) in the Eastern Canadian Arctic

I studied the breeding ecology and behavioral endocrinology of Ruddy Turnstones at East Bay, Southampton Island, Nunavut in 2002 and 2003. I documented breeding phenology, nesting success and predation rates and compared these results to other breeding sites. Although breeding activities were spread over a wider range of dates in 2003, the median dates for hatching and incubation onset were the same, despite differing spring snow conditions and weather. These data suggest that arthropod availability for chicks may be the most important influence on the timing of breeding. The East Bay population appeared to nest semi-colonially. Nest success was low, predation was high, and lemmings were scarce. The data from this study (and previous East Bay studies) supported the hypothesis which predicts fluctuations in avian nest success will be synchronous with small mammal populations, as predators switch to alternative prey (eggs and young) when primary prey (lemmings) is low. I also investigated several hormonal mechanisms associated with energy demand and sex-specific parental efforts to understand better how high latitude breeders meet energy demands. Normally, plasma corticosterone (CORT; the major energy-regulating hormone) is low, but can rise rapidly to help an individual through periods of potential stress (the adrenocortical response). Previous studies have shown some Arctic breeders reduce this response during critical breeding stages, possibly increasing the threshold of life-saving responses that may otherwise compromise breeding success (e.g. desertion). To look for hormonal patterns that may vary at different parental stages, blood samples were taken during mid-incubation and early brooding for CORT and prolactin (PRL; the major hormone associated with incubation behavior). Energetic condition was assessed by size-corrected body mass and key plasma metabolites associated with fattening, lipolysis, and/or protein mobilization. Relative incubation effort was assessed by 24-hr behavioral watches. Breeding pairs share incubation duties equally, and this is reflected in their similar patterns of CORT and PRL secretion. Collectively, adults showed a significant difference in the magnitude of the adrenocortical response between midincubation and early brooding. Baseline CORT was significantly higher (while PRL was significantly lower) during early brooding as compared to incubation. Metabolites did not vary with sex, body condition, hormone level or parental stage. An increase in baseline CORT during brooding may help individuals meet higher parental demands by facilitating additional foraging and feeding. The reduced adrenocortical response during brooding may be a mechanism to increase the threshold for abandonment when faced with few or no renesting opportunities. Finally, I investigated potential ecological and physiological influences on female brood desertion with the use of radiotelemetry and through visual observation. The timing of brood desertion was inversely related to hatch date, where broods hatching earlier deserted significantly later in the chick-rearing period. Energetic condition did not appear to be a factor affecting the timing of desertion. Timing of breeding may be the primary influence on female desertion decisions and I propose a model which predicts that pairs who initiate clutches earlier should have increased reproductive success, as biparental care in the early brooding period may increase chick survival.

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