Social dynamics of core members in mixed-species bird flocks change across a gradient of foraging habitat quality.

Kathryn E. Sieving,Nolan D. Lancaster,Todd M. Freeberg,Katherine E. (Gentry) Richardson,Jeffrey R. Lucas,Daniel P. Roche,Stephen G. Mugel

doi:10.1371/journal.pone.0262385

Kathryn E. Sieving, Nolan D. Lancaster + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0262385

Copy DOI

Abstract

Social associations within mixed-species bird flocks can promote information flow about food availability and provide predator avoidance benefits. The relationship between flocking propensity, foraging habitat quality, and interspecific competition can be altered by human-induced habitat degradation. Here we take a close look at sociality within two ecologically important flock-leader (core) species, the Carolina chickadee (Poecile carolinensis) and tufted titmouse (Baeolophus bicolor), to better understand how degradation of foraging habitat quality affects mixed-species flocking dynamics. We compared interactions of free ranging wild birds across a gradient of foraging habitat quality in three managed forest remnants. Specifically, we examined aspects of the social network at each site, including network density, modularity, and species assortativity. Differences in the social networks between each end of our habitat gradient suggest that elevated levels of interspecific association are more valuable in the habitat with low quality foraging conditions. This conclusion is supported by two additional findings: First, foraging height for the subordinate Carolina chickadee relative to the tufted titmouse decreased with an increase in the number of satellite species in the most disturbed site but not in the other two sites. Second, the chickadee gargle call rate, an acoustic signal emitted during agonistic encounters between conspecifics, was relatively higher at the high-quality site. Collectively, these results suggest an increase in heterospecific associations increases the value of cross-species information flow in degraded habitats.

Highlights

Broad foraging niches and plastic foraging behavior often facilitate the use of adaptive foraging strategies when animals face shifting resource availability and novel environments [1,2,3]
This, along with our previous finding that satellite species continued to flock with core species into the breeding season in a relatively poor-quality foraging habitat [24], suggests that habitat quality degradation increases the value of interspecific associations
Our observations of conspecific aggression and network structure of heterospecific core members along a gradient of habitat foraging quality support the Information and network-cohesion Hypothesis, which predicts that heterospecific associations will increase as adaptive responses to habitat degradation

Summary

Introduction

Broad foraging niches and plastic foraging behavior often facilitate the use of adaptive foraging strategies when animals face shifting resource availability and novel environments [1,2,3]. The tradeoff between interspecific competition and flocking benefits depends on the degree of foraging niche segregation within a flock [15,16], as well as the abundance and distribution of food, and predation risk [8,14,17]. For this reason, mixed-species flocking typically occurs when food availability is especially low or predation risk is especially high [8,18]. As such, mixed-species bird flocks in temperate climates tend to form during the winter season when food is scarce [19]

Methods

Results

Discussion

Conclusion