From static to dynamic ‘nest webs’: Changes in the architecture of an interspecific network of cavity-nesters over 12 years during an outbreak of Mountain Pine Beetle

COCKLE, KRISTINA L; KATHY MARTIN

Vancouver

Congreso; North American Ornithological Conference; 2012

University of British Columbia

In North American forest communities, 7–10 species of excavators, especially woodpeckers, generate a limited supply of tree cavities required for nesting by a rich assemblage of non-excavating cavity users. ‘Nest webs’ have been used since 1999 to describe the links among producers and users of tree cavities, but there has been little quantification of nest web architecture. We use network analysis on a 12-year data-set from interior British Columbia, Canada, to determine how nest-web properties change over time during a food pulse from an outbreak of Mountain Pine Beetle (Dendroctonus ponderosae). Prior to the beetle outbreak, non-excavator birds relied primarily on cavities excavated by Northern Flickers (Colaptes auratus), and management recommendations focused on preserving trees for flicker cavities. Over the course of the beetle outbreak, non-excavators increased their use of nesting cavities excavated by a variety of bark-insectivores that feed on beetles, resulting in reduced dominance of the Northern Flicker and an overall increase in network evenness. Our results show how a large-scale disturbance can lead to increased interaction diversity in a commensal interspecific network, and suggest that management strategies for cavity-nesters should be flexible enough to account for changes in the identity of key cavity producers in response to natural disturbance. By studying the dynamics of interspecies networks over time, we reveal important relationships that are missed with a static approach, and may be important for network resilience.