Sustaining Cavity-Using Species: Patterns of Cavity Use and Implications to Forest Management

Abstract

Many bird and mammal species rely on cavities in trees to rear their young or roost. Favourable cavity sites are usually created by fungi, so they are more common in older, dying trees that are incompatible with intensive �ber production. Forestry has reduced amounts of such trees to the extent that many cavity-using vertebrates are now designated "at risk. " e simple model of cavity use presented helps unite research �ndings, explain patterns of use, and clarify trade-o�s that can, or cannot, be made in snag management. Predictions generated are tested using data from over 300 studies. Implications to forest management are derived from the tests, including the following: ensure sustained provision of dying and dead trees, retain both conifers and hardwoods and a range of size and age classes, sustain a range of decay classes, ensure that some large trees or snags are retained, promote both aggregated and dispersed retention of dead and dying trees, meet dead wood requirements for larger species where intensive �bre production is not emphasized, do not do the same thing everywhere, and limit salvage logging aer tree mortality. e paper focuses on species breeding in the Paci�c Northwest, but draws on data from throughout those species' ranges.

Do increases in the availability of standing dead trees affect the abundance, nest-site use, and niche partitioning of great spotted and middle spotted woodpeckers in riverine forests?

“…However, changes in the abundance of middle spotted woodpecker have been positively correlated with winter temperatures (Wesołowski and Tomiałojć 1997). Our results are in line with earlier suggestions that the response of cavity nesters to snag density in hardwood stands seems to be weaker than in coniferous forests (Bunnell 2013). The lack of a positive effect of experimentally increased hardwood snag density, from 15 to 33 snags 10 ha -1 , on the abundance of cavity nesters, including four woodpecker species, has been found in a mixed mesophytic forest in North America (McPeek et al 1987).…”

The role of wood hardness in limiting nest site selection in avian cavity excavators

“…On average, nests of three-toed woodpeckers (P. dorsalis and P. arcticus) had harder sills than those of sapsuckers, which in turn had harder sill wood than Hairy Woodpecker, White-headed Woodpecker, and Northern Flicker nests. Despite these differences and their implications for nest site selection, our results suggest that researchers should be cautious about using excavator guilds (e.g., Ingold 1994, Dudley and Saab 2003, Bunnell 2013) without more study, particularly controlled tests in laboratory settings. This is partly because, despite differences in mean sill hardness, we observed a lot of overlap suggesting excavator guilds are overly simplistic.…”

“…We chose these species because they represent two presumed but unconfirmed guilds in excavation ability among PCEs. American Three-toed, Black-backed, and Hairy Woodpeckers have been classified as ''strong'' excavators Saab 2003, Edworthy et al 2012), compared to Northern Flicker, White-headed Woodpecker, and Williamson's Sapsucker (Saab and Dudley 1998, Schepps et al 1999, Bunnell 2013.…”

Natural cavity restoration as an alternative to nest box supplementation

“…land clearance and managed tree removal, frequently results in the decline of large old trees and the subsequent decrease of nesting sites (Gibbons et al ; Le Roux et al ; Plieninger et al ). As a result, many cavity‐using vertebrates are currently threatened (Bunnell ; Lindenmayer et al ). Not surprisingly, nest‐site supplementation by addition of nest boxes has become an increasingly common restoration strategy in modified landscapes, mainly in forested areas (Franzreb ; Harper et al ; Goldingay et al ; Le Roux et al ).…”