Convergence in foraging guild structure of forest breeding bird assemblages across three continents is related to habitat structure and foraging opportunities

Abstract

Comparisons of community structure across sites allow for the detection of convergent patterns and the selective forces that have produced them. In this study, we examined the foraging guild structure of birds breeding in forests on three continents-Europe, North America, and Australia, with largely phylogenetically distinct avifaunas. We examined two hypotheses: (1) the bird assemblages in the three geographically separated forested study sites should have similar foraging guild patterns to the extent to which environmental resources of these forests are similar, and (2) if bird assemblages in structurally similar forest habitats have undergone adaptive evolution, then radiation of species into guilds should have been caused by analogous selective resource gradients (factors). Bootstrapped cluster analysis (UPGMA) and bootstrapped principal coordinate analysis (BPCoA) of chord distances were employed to determine foraging guild structure for each assemblage, and to extract the significantly different factors responsible for segregation of species into guilds. Cluster analyses identified three analogous foraging guilds (ground and litter foragers, foliage gleaners, and trunk foragers) in each of the bird assemblages, supporting the first hypothesis of guild structure convergence. The BPCoA determined that two environmental factors (vertical resource allocation and spatial tree morphology gradients) were primarily responsible for segregation of species into guilds in these three geographically distant but structurally similar forests. These findings support the hypothesis that guild structures in forest bird assemblages largely reflect the similarities and differences in forest structure and the distribution and abundance of foraging resources, and result from largely adaptive evolution. Nomenclature: Bird nomenclature follows Dickinson (2003).

The winter foraging behaviour of birds in a mixed eucalypt forest and woodland on the Southern Tablelands of New South Wales

“…Absent from, or poorly represented in, the winter community considered in this paper are the nectar-feeder and aerial-forager/snatcher guilds recognized in the guild analyses of Holmes and Recher (1986) and Korňan et al (2013). The species forming these guilds in summer were either absent or present only in reduced numbers during winter.…”

“…The analysis of Holmes and Recher (1986) included body weight with four guilds separated by size; large and small ground foragers, and large and small aerial foragers. By ignoring body weight the number of guilds is reduced to seven, which is the same as obtained by Korňan et al (2013) using different statistical procedures, but the same data, if body weight is also excluded from their analysis. The guilds identified by Korňan et al (2013) are the same as reported by Holmes and Recher (1986), but the species composition of the guilds identified differed.…”

“…The seven guilds as recognized by Korňan et al (2013) are: I. Nectar-feeders (3 species); II. Ground-gleaners (10); III.…”

“…In this paper, I present data on the foraging ecology and guild structure of a eucalypt forest and woodland bird community in southeastern New South Wales during winter. Earlier papers described the foraging ecology of this community during the spring/ summer breeding season Recher and Holmes 1986;Holmes and Recher 1986;Korňan et al 2013). Here I compare foraging behaviour and guild structure between breeding and non-breeding seasons.…”

“…Foraging relationships among birds can be described using cluster analysis whereby bird species are grouped according to the similarity the manoeuvre/substrates each uses. The groups can then be used to define guilds, with a guild being a cluster of species using similar food resources (Root 1967;Holmes and Recher 1986;Korňan et al 2013). …”