Abstract
Abstract The availability of suitable cavities and substrate for hole construction can limit the populations of birds that rely on tree hollows to reproduce. Several studies have focused on the effects of types of habitats, and types of human disturbances on cavities abundance, but the effect of successional stages in the Atlantic Forest has been poorly addressed. In this study we aimed to compare the availability and biometric characteristics of tree cavities between primary and mid-successional stage sites in an Atlantic Forest area from southeastern Brazil. Based on nest characteristics described in the literature, we inferred if hollows present in secondary sites could harbor the large secondary-nester Atlantic Forest birds, with special attention to toucans and hawks. From September 2016 to April 2017, 96 cavities were sampled, 67 in the primary, and 29 in the secondary plots. Our data revealed that the communities of cavity-nester birds in mid-successional stage areas may be more affected by the reduced cavity availability than by cavities quality, as the number of cavities in these sites was less than half than that found in mature forests. We also provide evidences that the largest cavity nesters, such as the biggest hawks, might have limited nesting possibilities in mid-successional stage areas especially due to small cavity entrances, which may have important reflects in conservation strategies.
Highlights
Bird species that use tree cavities for nesting can be classified as i) excavators, or primary cavity nesters, and ii) non-excavators, or secondary cavity nesters
We addressed the following questions: i) Does cavity availability differ between mid-successional stage and primary Atlantic Forest sites? ii) Does the amount of dead trees differ between these areas? iii) Do cavity measurements differ between these successional stages? iv) Could cavities in the mid-successional stage sites harbor the entire guild of cavity-nesting Atlantic Forest birds?
Our main prediction of reduced number of cavities in mid-successional stage areas was corroborated and our data suggested that only advanced successional stage, or primary areas, may present the density of cavities expected for natural Atlantic Forest habitats
Summary
Bird species that use tree cavities for nesting can be classified as i) excavators, or primary cavity nesters, and ii) non-excavators, or secondary cavity nesters. Timber management practices based on the exploitation of decaying trees have caused disastrous declines in cavity-nesting birds in Europe and North America (Dobkin et al 1995, Aitken et al 2002, Franco et al 2005). These are evidences that forest type, successional stage, and degree of human disturbance are key elements for cavity nests availability and for the persistence of cavity‐nesting birds (Cornelius et al 2008)
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