Cavity-nesters

Cavity-nesting birds make up a sizeable portion of the avian communities in the longleaf pine forests in which RCWs live. Cavity-nesters include not only cavity-excavating species like woodpeckers, but also non-excavating, secondary cavity-nesters. Coniferous forests in North America are unusual in the paucity of “natural” tree holes that arise through fungal decay and other processes, and thus the extent to which secondary cavity-nesters rely on excavated cavities for nest sites. The RCW is the only species of woodpecker that excavates cavities exclusively in living pine trees. By doing so it functions as a keystone species, producing a resource for secondary cavity-nesters (i.e., cavities in living pines) that is not available in most systems. We are investigating the relationships between trees (living pines, dead pines, dead hardwoods), cavity excavators and secondary cavity nesters that comprise what is termed the nest web (analogous to a food web) in longleaf pine forests with an emphasis on the impact of RCWs on the diversity and abundance of cavity-nesting birds. Current graduate student Noah McNeil is studying another member of the cavity-nesting community, the Brown-headed Nuthatch, with a focus on its participation in mixed species flocks. We are also investigating the effectiveness of the RCW as an umbrella species by assessing the impact of management of habitat for RCWs on the diversity of abundance of other bird species found in these forests.

Relevant Publications:

Blanc, L. A. and J. R. Walters. 2008. Cavity excavation and enlargement as mechanisms for indirect interactions in an avian community. Ecology 89:506-514.

Blanc, L. A. and J. R. Walters. 2008. Cavity-nest webs in a longleaf pine ecosystem. Condor 110:80-92.

Former lab member Maya Wilson recently studied the nest web in pine forests in the northern Bahamas. This nest web is of particular interest because it contains only a few species that potentially have strong interactions between them. Of particular interest is the possibility that these interactions may limit the abundance of the endangered Bahama Swallow, a secondary cavity-nester. The swallows depend almost exclusively on cavities excavated in dead pines by one excavator, the Hairy Woodpecker. Dr. Wilson is assessing this dependency as one of several possible factors that may be responsible for the decline of the Bahama Swallow in hopes of devising an effective recovery strategy for this rare bird.

Relevant Publications:

Wilson, M. and J. R. Walters. 2020. Cavity use and breeding biology of the endangered Bahama Swallow (Tachycineta cyaneoviridis): implications for conservation. J. Field Ornithol. 91:118-129.

Nest webs in tropical systems are complex, containing a large number of species with an array of interactions between them. Typically they include many secondary cavity-nesters that use natural tree holes rather than excavated cavities. Current graduate student David Millican is studying a tropical nest web in dry forest in Namibia that contains many secondary cavity-nesters that are much larger than any of the cavity excavators and thus depend on natural holes in a system where large trees are scarce. David is studying the dynamics of this nest web, including assessing the possible effects of forest management on secondary cavity-nester diversity and abundance due to impacts on availability of nest holes.