The Wildlife Society has made available videos of presentations from its 2014 conference, and they’re a terrific resource for learning, teaching, and networking. To get started, check out Rebecca Kern from the University of Delaware presenting a bit of her PhD work on factors affecting nest survivorship in Saltmarsh and Seaside sparrows.
Access to the video might require membership to The Wildlife Society. If it doesn’t work for you, here at least is the abstract!
Effective conservation of endemic tidal marsh birds, species of high conservation concern, requires the identification of factors limiting reproduction and survival. Saltmarsh (Ammodramus caudacutus) and Seaside (A. maritimus) sparrows breed sympatrically in northeastern marshes and must minimize two competing forces – nest flooding and nest predation – to reproduce successfully. We used a Markov Chain framework to simultaneously model nest survival probability and cause-specific (flooded or depredated) failure probabilities for these species in New Jersey. We ranked models using AICc and model weight to compare the importance of nine covariates in determining nest fate for each species. We found that for Seaside Sparrows (n=170 nests), flooding was most-strongly influenced by date and predation was most affected by study site. Seaside Sparrow nest flooding was 12 times more likely in May than in July, and nest predation was greatest within 150 m of forested upland/developed land. For Saltmarsh Sparrows (n=161 nests), days since new moon, high marsh cover, and nest canopy cover were the most important predictors of nest survival. Saltmarsh nests were least likely to flood when initiated soon after a new moon, which brings the highest tides. Nest predation was greater for nests with high marsh cover (Spartina patens and Distichlis spicata) within 1 m2 of the nest, while nests with more canopy cover had lower predation. Over the 25-day nesting period, Saltmarsh Sparrows had lower nest survival than Seaside Sparrows (0.20±0.04 versus 0.27±0.06) because they had greater losses to flooding. Both species experienced similar predation probabilities (0.37±0.05 and 0.38±0.09), but flooding was 3.5 times more likely for Saltmarsh Sparrows (0.21±0.04 versus 0.06±0.03). These observed differences in reproductive success driven by a trade-off between predation and flooding may help to elucidate the evolution of divergent mating system strategies for these two tidal marsh obligate birds.