Abstract
Many animals require tree cavities for breeding and these sites may be reused by a diversity of secondary nesters over a timespan of decades. It is unknown whether the reuse of holes changes their desirability as nest sites. We hypothesized that some species, cavity degraded the quality of holes by filling them with coarse nest material or waste whereas other species, cavity cleaners, might prolong the use of a hole by removing debris or enlarging the hole. Using data gathered during 22 years from a field study in central British Colombia, we analyzed long-term patterns of occupancy in relation to their sequential use by bird and mammal species, grouped by traits. Patterns of occupancy were variable with 49% of 875 large-sized holes (excavated by northern flickers Colaptes auratus and pileated woodpeckers Dryocopus pileatus) and 19% of 672 smaller-sized holes incorporating runs of sequential use that lasted up to 18 years. But 11-25% of cavities also had gaps of 3-13 years between occupancies. Mammals, raptors and European starlings, consistent with the hypothesis they were destroyers, occupied cavities as terminal users and before gaps more often than expected by chance. The pattern of occupancy by northern flickers was random in relation to gaps or prior use by other species so, although flickers did not target old holes to clean, neither did they avoid them. Small cavities that were renovated by flickers into larger cavities had double the reuse rate. Runs of occupancy that involved only cavity-destroying species were shorter than runs that involved periodic use by flickers, suggesting the woodpecker, through its cleaning and renovation, prolonged the use of such holes.
Highlights
Tree cavities are a multi-annual resource that is often in high demand among forest vertebrates for breeding or roosting; individual cavities may be used more than 20 times over greater than three decades (Cockle et al, 2019)
In North America, excavators create most of the cavities that are subsequently reused by a diverse assemblage of secondary cavity nesters which cannot excavate their own holes (Martin et al, 2004; Cockle et al, 2011)
Long-term studies monitoring the use of individual cavities over time allow detailed analysis of the dynamics of these “nestweb” systems (Martin et al, 2004)
Summary
Tree cavities are a multi-annual resource that is often in high demand among forest vertebrates for breeding or roosting; individual cavities may be used more than 20 times over greater than three decades (Cockle et al, 2019). Cavities in trembling aspen Populus tremuloides trees in central British Columbia lasted on average seven years in dead trees and more than 15 years in living trees (Edworthy et al, 2012). During their lifespan, cavities may change in size and decay state and different species of secondary cavity nesters may prefer cavities of different ages. The changing physical properties of cavities as a result of their aging and decay (Edworthy and Martin, 2014) may affect the identity of the species that occupy them over long timespans; it is unknown how the sequential use of holes from 1 year to the may be affected by the use by various types secondary cavity nesters
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