Cross-scale interactions (CSI) may be common, but they have received relatively little research attention. We explored CSI effects of sub-regional climate (breeding season temperature and precipitation, spring precipitation, and winter temperature) and landscape-scale exurban cover on four declining forest bird species. Both climate and exurbanization are known to influence forest birds. The increased availability of resources, such as food, in a region with a suitable climate may moderate the negative influence of habitat fragmentation due to exurbanization. In the face of climate change and increasing exurbanization, it is important to know how these factors may interact across scales to influence avian persistence. We used data from the North American Breeding Bird Survey (BBS) to calculate species’ persistence during 2009-2013 across six EPA Level II Ecoregions in the eastern United States. Species’ median and maximum natal dispersal distances were used respectively to create landscape and sub-regional scale buffers around the BBS routes, within which environmental variables were measured. Twenty-one a priori ordinary least-squares regression models were built and assessed using AICc statistics.
Results/Conclusions
The American Redstart (Setophaga ruticilla) was not influenced by CSIs. The Kentucky Warbler (Geothlypis formosa) was influenced by CSIs involving breeding season climate (maximum temperature and precipitation), the Black-and-White Warbler (Mniotilta varia) was influenced by CSIs involving spring precipitation, and the Scarlet Tanager (Piranga olivacea) was influenced by CSIs involving winter temperature. As one example of a CSI, we found that regions with warmer winter temperatures had higher persistence of the Scarlet Tanager, but the species’ persistence decreased with increasing exurban cover; whereas in regions with lower winter temperatures, the species’ persistence increased with increasing exurban cover. In regions with warmer winters, there may have been more food for the Scarlet Tanager during the breeding season because more overwintering invertebrates may have survived; however, increasing exurbanization may have fragmented habitat and reduced Scarlet Tanager persistence. People living in exurban areas in colder regions may continue supplemental feeding of birds during summer, and this may have increased Scarlet Tanager persistence. Our results suggest that CSIs may be common between major drivers of biodiversity change. Understanding the influence of CSIs, especially those involving climate and exurban cover, may improve the effectiveness of landscape-management efforts for declining bird species.