Microclimate and Ecological Factors Influencing Habitat Selection in Chimney Swifts, Chaetura Pelagica
Holmes, Jesse M.
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Chimney swifts (Chaetura pelagica) are voracious aerial insectivores which roost in vertical shafts such as hollow trees or chimneys. The International Union for Conservation of Nature (IUCN) has listed the chimney swift as near threatened due to recent sudden declines in population size. Due to limited accessibility of roosting sites and the almost completely aerial lifestyle of this bird, little data exists on the microclimatic requirements of this species. This makes it much more difficult to determine how future climatic changes may affect populations during the breeding season. My objectives for this study were 1) to determine whether there is a difference in occupancy in chimneys with birds between breeding and post-breeding sessions, 2) whether there is a relationship between chimney microclimate (specifically temperature and relative humidity) and selection by chimney swifts, and 3) whether there is a relationship between roost habitat selection and habitat characteristics (size and proximity of water sources, canopy cover near or over chimneys, and chimney characteristics including size, location, color, and composition). I investigated chimney swift roost selection during the summer of 2015 in Johnson County, Missouri. Using HOBO U23 Pro v2 data loggers, I recorded microclimate data for twelve potential roost chimneys: seven plus two capped chimneys in Warrensburg, MO; one 10 miles north of Warrensburg; and two in Holden, MO. Bird counts were conducted at all but the two capped chimneys twice during the summer: May-June and August-September. I also observed the surrounding habitat for each chimney and digitized water bodies within 1km, 3km, and 5km of all uncapped chimneys. Occupied chimneys had statistically significant lower average daily temperatures, significantly lower daily temperature variation, and significantly lower daily relative humidity variation during the breeding session. Occupied chimneys also had significantly larger openings. Most chimneys did not have trees or powerlines surrounding, but the two that did had no birds detected. Chimneys with birds all had large (< 10 hectares) water bodies between 1-3 km of the chimney, while chimneys without birds typically had large bodies of water further away, if at all. These findings suggest a relationship between roost microclimate and roost selection, however that is not the only factor which may affect roost selection. Size and location of chimney, lack of surrounding trees, and a large water body within 1-3 km all seem to be important. Further research is necessary to determine the extent to which each of these factors influence site selection in chimney swifts.