Individual Nest Site Preferences Do Not Explain Upslope Population Shifts of a Secondary Cavity-Nesting Species

Geographic ranges of plants and animals are shifting due to environmental change. While some species are shifting towards the poles and upslope in elevation, the processes leading to these patterns are not well known. We analyzed 22 years of western bluebird (Sialia mexicana) data from a large nest box network in northern New Mexico at elevations between 1860 m and 2750 m. This population has shifted to higher elevations over time, but whether this is due to changes in nesting behavior and preference for higher elevation within the population or driven by immigration is unclear. We banded adults and nestlings from nest boxes and examined nesting location and elevation for individual birds captured two or more times. Most recaptured birds nested at the same nest boxes in subsequent years, and the number of birds that moved upslope did not significantly differ from the number that moved downslope. Fledglings moved greater distances and elevations than adults, but these movements were not upslope specific. Female fledglings showed greater changes in elevation and distance compared to male fledglings, but again, movements were not consistently upslope. The upslope shift in this population may be due to birds immigrating into the population and not from changes in individual nesting behavior.

Changes in the nest sites of White Stork (Ciconia ciconia) in Hungary

The breeding strategies of the White Stork changed drastically during the past decades: a decreasing number of individuals nest on traditional nest sites – trees, roofs, chimneys, whereas electricity poles are increasingly selected. Here we analysed long-term breeding data of White Storks breeding in six Hungarian counties to detect patterns in nest site preferences in Hungary. According to our results, the shift to preference for electricity poles was shown at the same rate in every county, independently from the proportion of original nest sites. After 2000, although electricity poles dominated everywhere, the proportion of nest on poles without platform increased, despite the abundance of available empty platforms. To explain this pattern, we propose that White Storks show a preference for viewpoints, thus choosing to breed as near as possible to optimal habitats, regardless of nest site types. Therefore, conservation measures concerning the nest sites of this species should include preliminary habitat analysis.

Directional selection and repeatability in nest-site preferences of Semipalmated Plovers (Charadrius semipalmatus)

Using marked individuals, we assessed directional selection and repeatability of nest-site characteristics of Semipalmated Plovers (Charadrius semipalmatus Bonaparte, 1825) on Akimiski Island, Nunavut, Canada, 2002–2005, to test the hypothesis that long- and short-term selection patterns were in the same direction. Plovers placed nests in microsites (1 m2 scale) with more pebbles and less bare mud and vegetation than what was available in the environment, indicating long-term selection for these features. Linear (directional selection) effects were stronger than quadratic (stabilizing or disruptive) effects in 3 of 4 years and in the analysis of all data. In the combined 4-year sample, significant directional selection occurred in the opposite direction than that present when comparing used and available sites. Birds with more bare mud and vegetation and fewer pebbles at their nest sites were more successful than birds with pebbled nest sites. Repeatability of nest-site preferences was low and nonsignificant. Neither successful nor unsuccessful pairs chose significantly different nest-site characteristics in subsequent nesting attempts, but options for moving to different nest sites may be limited by interannual site fidelity. Wide individual variability and low repeatability of nest-site characteristics suggests behavioral flexibility in the population. Applying quantitative genetic techniques to patterns of habitat selection may allow researchers to predict the degree to which animals can adjust to changing environments.