Abstract
Global monitoring of biodiversity and ecosystem change can be aided by the effective use of indicators. Tree-cavity excavators, the majority of which are woodpeckers (Picidae), are known to be useful indicators of the health or naturalness of forest ecosystems and the diversity of forest birds. They are indicators of the latter due to shared associations with particular forest elements and because of their role in facilitating the occurrence of other species through the provision of nesting cavities. Here, we investigated whether these positive correlations between excavators and other forest birds are also found at broad geographical scales. We used global distribution maps to extract richness estimates of tree-cavity nesting and forest-associated birds, which we grouped by zoogeographic regions. We then created generalized least-squares models to assess the relationships between these groups of birds. We show that richness of tree-cavity excavating birds correlates positively with that of secondary cavity nesters and other forest birds (generalists and specialists) at global scales, but with variation across zoogeographic regions. As many excavators are relatively easy to detect, play keystone roles at local scales and are effective management targets, we propose that excavators are useful for biodiversity monitoring across multiple spatial scales and geographical regions, especially in the tropics.
Highlights
Forests worldwide are facing increasing anthropogenic pressures, with both a rapid decline in the area of natural forests and a royalsocietypublishing.org/journal/rsos R
60 97 89 94 84 83 82 88 100 100 100 100 83 73 77 84 76 78 84 87 88 100 96 99 mean Spearman ρ. These relationships differed in both strength and characteristics across zoogeographic regions, they presented comparable patterns concerning the potential role of excavators to serve as indicators for avian biodiversity
Relationships between excavators and non-cavitynesting forest birds were strong in most regions, often stronger than those between excavators and secondary cavity nesters
Summary
Forests worldwide are facing increasing anthropogenic pressures, with both a rapid decline in the area of natural forests and a royalsocietypublishing.org/journal/rsos R. To monitor changes in forest ecosystems and their denizens, we often look at specialized animals that require the availability of specific habitat structures and processes running across long temporal and large spatial scales for longterm persistence [6], such as birds that respond to a loss in overall forest cover and to changes in forest health, quality and integrity [7,8,9,10] Excavators such as woodpeckers, barbets, nuthatches, trogons and certain parrot species—among which woodpeckers are the most numerous group [11]—may be especially effective indicators due to their associations with particular forest elements and their role in facilitating the presence of other species through the provision of nest cavities. We may question whether excavators are universally effective indicators, especially of overall levels of biodiversity, in all geographical regions of the globe or for all forest types [15]
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