Global relationships between tree-cavity excavators and forest bird richness

Abstract

<jats:p>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.</jats:p>

The Role of Monk Parakeets as Nest-Site Facilitators in Their Native and Invaded Areas

“…These complex facilitative interactions could be considered as inquilinism, in which some species (nest inquilines or tenants) use nests of other species and they can show parasitic, commensalistic, and mutualistic interactions with their hosts [26,27]. However, to our knowledge, this kind of inquilinism has not been considered in birds, although similar interactions from other nest builder birds have been recorded [28][29][30].…”

Unravelling the cavity‐nesting network at large spatial scales: The biogeographic role of woodpeckers as ecosystem engineers

“…The important role of woodpeckers has been highlighted at a local scale, where positive feedback with animal and fungus diversity has been found in different forest ecosystems worldwide (Lõhmus, 2016; Mikusiński et al., 2001; van der Hoek et al., 2017). However, their role on the spatial patterns of cavity‐nesting networks has remained less explored, with a few studies exploring patterns of co‐occurrences among cavity excavators and secondary users (van der Hoek et al., 2020), and discussing the influence of climate and biomes on nesting‐cavity network at regional scales (Ibarra et al., 2020). In regions with a low richness of woodpecker species, like southern South America (Ilsøe et al., 2017), the local loss of a few woodpecker species may cause important impacts on the facilitation networks of cavity users.…”

Density and characteristics of tree cavities inside and outside Volcanoes National Park, Rwanda

“…Indeed, our estimate of 134.7 trees per hectare is well below the interquartile range of tree densities for either tropical moist or dry forest (lower quartile cut‐off >250 trees per hectare for either forest type, Crowther et al, 2015). In addition, but related to low tree availability at high elevations near the treeline ecotone, there is a potentially low abundance and richness of excavators (avifauna) in VNP (van der Hoek et al, 2021; van der Hoek, Faida, et al, 2020; van der Hoek, Gaona, et al, 2020).…”

“…Tree cavities, either excavated by woodpeckers (Picidae) or other birds or created by mechanical damage and fungal decay, are useful for many animals as substrates for shelter or nests (Cockle, Martin, & Wesołowski, 2011; Cockle, Martin, & Wiebe, 2011; Trzcinski et al, 2021; van der Hoek et al, 2017; van der Hoek, Faida, et al, 2020; van der Hoek, Gaona, et al, 2020). Cavity users may be classified as excavators (e.g., aforementioned woodpeckers) or secondary cavity users (e.g., parrots [Psittaciformes]), the latter depending on existing cavities (Martin & Eadie, 1999).…”

“…Multiple biotic and abiotic factors drive spatial variation in tree cavity availability. First, tree cavity availability has been linked to woodpecker abundance and diversity (Styring & Zakaria, 2004), though the evidence is skewed toward temperate ecosystems of the northern hemisphere, and excavator richness itself may be indicative of the diversity of the wider forest bird community (Drever et al, 2008; van der Hoek, Faida, et al, 2020; van der Hoek, Gaona, et al, 2020). Second, tree cavity density may vary across landscapes because of variations in tree species and characteristics (Schepps et al, 1999; Zheng et al, 2018).…”