Nest temperature fluctuations in a cavity nester, the southern ground-hornbill

Roost sites of chimney swift (Chaetura pelagica) form large-scale spatial networks

Several biodiversity-centered metrics exist to quantify the importance of landscape and habitat features for conservation efforts. However, for species whose habitat use is not quantified by these metrics, such as those in urban areas, we need a method to best identify features for targeted conservation efforts. We investigated the use of social network analysis (SNA) to identify and quantify these critical habitat features. We used SNA to identify network existence in chimney swift (Chaetura pelagica) roost usage, quantify the importance of each roost site, and evaluate the impact of the loss of key sites. We identified a network consisting of ten chimney swift roosts in southern Nova Scotia, Canada, and found that 76% of swifts used more than one roost throughout the breeding season. We also isolated three key (most connected) roost sites. We evaluated the effect of loss of these key sites on the network by using a Wilcoxon-Pratt signed-rank test and by analyzing the structure of the subsequent network. We found that connections between roosts and the structure of the network were significantly affected by the loss of these key sites. Our results show that SNA is a valuable tool that can identify key sites for targeted conservation efforts for species that may not be included in conservation efforts focused purely on biodiversity.

Does temperature variation influence nest box use by the eastern pygmy-possum?

Cavity-using birds and mammals reliant on nest boxes may be negatively affected by the poor thermal buffering of nest boxes. I investigated whether nest box use by the eastern pygmy-possum (Cercartetus nanus) over a 4-year period was influenced by maximum ambient temperature, which ranged from 15.6 to 34.9°C during survey occasions. Occupancy modelling of 144 site detections over 30 survey occasions suggested that a model that included maximum temperature had little support whereas a model involving time-varying detection (i.e. detection differed across sample occasions) was the most plausible. I also investigated how temperatures in nest boxes and tree hollows varied over the four hottest days of summer, including one day when the temperature reached 40.6°C. Maximum temperatures were 3–4°C cooler in plywood nest boxes and 5–8°C cooler in tree hollows compared with ambient temperatures. Together, these results suggest that eastern pygmy-possums using nest boxes in coastal areas are unlikely to experience heat stress. Cavity-using species are a heterogeneous group such that empirical studies are required to identify those that may be vulnerable to heat stress if nest boxes are used to provide population support.

Ambient temperature preferences of chimney swifts (Chaetura pelagica) for Nest Site Selection

Chimney swift (Chaetura pelagica) populations are declining rapidly, with no clear indication as to why. Reduced availability of nesting habitat (chimneys) was thought to be a limiting factor for this threatened species, but data from Ontario, Canada did not support this hypothesis. If availability is not limiting, then perhaps habitat quality may play a role. We examined the thermal aspect of chimneys that are used by nesting swifts. To do so, we identified upper and lower thermal limits influencing the selection of chimneys for nesting. Across Nova Scotia and New Brunswick, we deployed temperature loggers in 19 chimneys, 11 of which contained chimney swift nests and 8 that were deemed suitable for nesting but were not occupied. Temperature readings were recorded at 30-min intervals from 23 June to 15 September 2017. We found that chimney occupancy by swifts was negatively correlated with maximum and mean chimney temperature. We did not find a relationship between occupancy and minimum temperature, temperature fluctuations, or chimney material. These results indicate that chimney swifts are preferentially selecting cooler chimneys for nesting.