Incubation is an important component of avian parental care and slight changes in incubation temperature can aff ect off spring phenotype. Although many extrinsic and intrinsic factors may generate variation in incubation temperature, they remain underexplored under natural conditions. Using a robust data set encompassing 55 nests, 22 816 behavioral observations, and Ͼ 1 million paired ambient and egg temperatures, we describe the relationships among abiotic factors, female incubation behavior, incubation temperature, and incubation period for tree swallows Tachycineta bicolor . We report a large amount of individual variation in incubation behaviors and average incubation temperatures for our study population. Th e average on-bout incubation temperature was 34.1 ° C, with daily egg temperatures ranging from 18.0 -39.2 ° C. Females modulated the number of times they left the nest and the amount of time they stayed off the nest according to interactions between precipitation and temperature patterns. Models generated from our observations predicted that the number of female off -bouts was the lowest under warm and dry conditions while more off -bouts were taken under cold and dry or warm and wet conditions. During cold and dry conditions, females stayed off their nest ∼ 4 times longer than under warm and dry conditions. However, this pattern was reversed under periods of rainfall; females tended to take shorter off -bouts when it was rainy and cold compared to longer off -bouts during warmer rain events. Furthermore, variation in female behavior was associated with diff erences in overall incubation temperature such that females that maintained greater incubation constancy produced higher incubation temperatures at a given ambient temperature than those that displayed lower incubation constancy. Our results provide perspective on the timing of breeding, as some of the advantages of breeding early may be countered by cooler, early season temperatures and precipitation that cause reproducing females to favor self-maintenance at a potential cost to optimal incubation temperatures for off spring development.

No abstract

Disease is among the leading causes of global amphibian population declines, and may contribute to declines of the giant hellbender salamander (Cryptobranchus alleganiensis). We provide some of the first information about how hellbenders physiologically respond to end- and ecto- parasites, insights that could be critical to their conservation.

Hellbenders Cryptobranchus alleganiensis are critically imperiled amphibians throughout the eastern USA. Rock-lifting is widely used to monitor hellbenders but can severely disturb habitat. We asked whether artificial shelter occupancy (the proportion of occupied shelters in an array) would function as a proxy for hellbender abundance and thereby serve as a viable alternative to rock-lifting. We hypothesized that shelter occupancy would vary spatially in response to hellbender density, natural shelter density, or both, and would vary temporally with hellbender seasonal activity patterns and time since shelter deployment. We established shelter arrays (n = 30 shelters each) in 6 stream reaches and monitored them monthly for up to 2 yr. We used Bayesian mixed logistic regression and model ranking criteria to assess support for hypotheses concerning drivers of shelter occupancy. In all reaches, shelter occupancy was highest from June-August each year and was higher in Year 2 relative to Year 1. Our best-supported model indicated that the extent of boulder and bedrock (hereafter, natural shelter) in a reach mediated the relationship between hellbender abundance and shelter occupancy. More explicitly, shelter occupancy was positively correlated with abundance when natural shelter covered <20% of a reach, but uncorrelated with abundance when natural shelter was more abundant. While shelter occupancy should not be used to infer variation in hellbender relative abundance when substrate composition varies among reaches, we showed that artificial shelters can function as valuable monitoring tools when reaches meet certain criteria, though regular shelter maintenance is critical.