Climate change, including directional shifts in weather averages and extremes and increased interannual weather variation, is influencing demography and distributions for many bird species. The Ouachita Mountains ecoregion in southeast Oklahoma and west-central Arkansas contains 2 populations of the Red-cockaded Woodpecker (Dryobates borealis, RCW), a federally endangered, cooperatively breeding species. Since this region is at the RCW's northwestern range periphery, ecological thresholds likely are limiting for the species. Therefore, populations in this region may be more sensitive to climate change-associated weather variation and unpredictability. We used 26 years of nesting data (1991–2016) from the 2 RCW populations to determine if interannual weather variation has affected nesting phenology and productivity. For each population, we used daily temperature and precipitation data for 3 periods (30 and 60 days before nesting; 40 days overlapping the nesting period) to determine how weather influences median nesting date and average clutch size and numbers of fledglings. In a separate analysis, we used shorter time windows with individual nests as replicates to determine how discrete weather events (e.g., minimum and maximum temperatures and intense precipitation events) affect nest success and partial brood loss. For both Oklahoma and Arkansas populations, warmer early spring temperatures generally advanced nesting and increased clutch size and fledgling number. However, the effects of average precipitation varied depending on the amount and duration of precipitation in different time periods. At the nest level, most variables reflecting discrete temperature and precipitation events were unrelated to nest success and brood loss, suggesting that factors other than weather (e.g., habitat quality and predation) more strongly influenced the nesting output of individual RCW broods. Our results indicate RCWs are responding to interannual weather variation in complex and variable ways. However, warming trends may generally be having positive effects on the species at the northwestern edge of its range.
LAY SUMMARY
Climate change is influencing distributions and demography for many bird species. Understanding effects on populations at the edge of species' ranges will be crucial for adapting management to prevent climate-caused declines and extinctions.
For the endangered Red-cockaded Woodpecker, we used 26 years of nest monitoring data to evaluate how interannual climate variation has affected nesting timing and productivity at the northwestern edge of the species' range.
Warmer temperatures in early spring generally advanced Red-cockaded Woodpecker nesting dates and increased nest productivity. Precipitation effects were variable, depending on the amount and duration of rainfall in different time periods before and during the nesting season.
Although climate effects on Red-cockaded Woodpecker nesting ecology appear complex, conditions may be changing in ways that increase nest productivity at the northwestern edge of the species' range. Managing habitat in this part of the range may become increasingly important to Red-cockaded Woodpecker conservation as climate change continues.
