Long-term phenology of two North American secondary cavity-nesters in response to changing climate conditions

Abstract

Wildlife populations can respond to changes in climate conditions by either adapting or moving to areas with preferred climate regimes. We studied nesting responses of two bird species, western bluebird (Sialia mexicana) and ash-throated flycatcher (Myiarchus cinerascens), to changing climate conditions (i.e., rising temperatures and increased drought stress) over 21 years in northern New Mexico. We used data from 1649 nests to assess whether the two species responded to changing climate conditions through phenological shifts in breeding time or shifts in nesting elevation. We also examined changes in reproductive output (i.e., clutch size). Our data show that western bluebirds significantly increased nesting elevation over a 19-year period by approximately 5 m per year. Mean spring temperature was the best predictor of western bluebird nesting elevation. Higher nesting elevations were not correlated with hatch dates or clutch sizes in western bluebirds, suggesting that nesting at higher elevations does not affect breeding time or reproductive output. We did not observe significant changes in nesting elevation or breeding dates in ash-throated flycatchers. Nesting higher in elevation may allow western bluebirds to cope with the increased temperatures and droughts. However, this climate niche conservatism may pose a risk for the conservation of the species if climate change and habitat loss continue to occur. The lack of significant changes detected in nesting elevation, breeding dates, and reproductive output in ash-throated flycatchers suggests a higher tolerance for changing environmental conditions in this species. This is consistent with the population increases reported for flycatchers in areas experiencing dramatic climate changes.

2019 Results for Avian Monitoring at the Technical Area 36 Minie Site, Technical Area 39 Point 6, and Technical Area 16 Burn Ground at the Los Alamos National Laboratory

“…TA-39 is the lowest elevation treatment site and occupancy has been decreasing over time at this site and surrounding areas of the avian nestbox network. Wysner et al (2019) found that Western Bluebirds, one of the target species of the network, have increased their nesting elevation over time in the study area. Western Bluebirds have the highest occupancy rates throughout the nestbox network, and the shift in nesting elevation could be driving the lower occupancy rates at TA-39.…”

Sex ratio of Western Bluebirds (Sialia mexicana) is mediated by phenology and clutch size

“…In the same population of Bluebirds (with a much larger number of broods), clutch size decreased throughout the breeding season (Wysner et al . 2019). These patterns may be due to lack of food (Decker et al .…”

A field guide for aging passerine nestlings using growth data and predictive modeling

“…Bluebirds also use nest boxes for breeding when there is cavity competition (Brawn and Balda 1988;Brawn 1991) or when there is loss of breeding habitat (Keyser et al 2004). Nest box programs not only provide suitable nesting locations, but they also provide a mechanism for data collection and a way to monitor and evaluate environmental and anthropogenic impacts to populations over long time periods (Musgrave et al 2019;Wysner et al 2019).…”