Woodpeckers, wood decay, and the resilience of nest web communities

COCKLE, KRISTINA L; MARTIN, KATHY

Conferencia; 8th International Woodpecker Conference; 2019

Nearly 1900 bird species require tree cavities for nesting. Non-excavators (such as toucans, owls) are linked to the organisms that produce cavities (including woodpeckers, other avian excavators, and decay organisms) in complex ecological networks or nest webs. Conserving these networks in the face of global change requires an understanding of their structure and dynamics. Here, we draw on decades of research in North and South American forests to explore the roles of woodpeckers in the structure and function of nest web communities. Woodpeckers are the primary source of cavities throughout much of North America, but, at first glance, they appear to play only a minor role in producing cavities in forests outside North America (e.g., 0-20% of cavities in many forests of South America, Europe, and Oceania). In globally-endangered old-growth Atlantic forest of Argentina, woodpecker cavities persisted 10 years for non-excavated cavities), comprised 7% of nest sites used by nonexcavators, and supported only 0.3 species of non-excavators, on average, across their lifetimes (vs. 1.5 for non-excavated cavities). With increasing human disturbance to the forest, however, cavity supply declined dramatically and woodpecker cavities took on an increasing role,comprising 57% of nest sites used by non-excavators in isolated trees on farms. In Interior British Columbia, Canada, woodpeckers were consistently important facilitators in the nest web; however, species? roles shifted inresponse to a bark beetle outbreak, and the Northern Flicker, a facultative excavator, dramatically increased cavity production following the destruction of cavities in wildfires. We conclude that healthy woodpecker populations may play a critical role in regulating cavity supply, while rich woodpecker assemblages can offer redundancy in cavity production. We propose that woodpeckers act as agents of resilience in nest webs, allowing non-excavators to survive in otherwise cavity-poor habitats, and increasing the ability of nest webs to respond dynamically to disturbance.