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Although lowland tropical rain forests were once widely believed to be the archetype of stability, seasonal variation exists. In these environments, seasonality is defined by rainfall, leading to a predictable pattern of biotic and abiotic changes. Only the full annual cycle reveals niche breadth, yet most studies of tropical organisms ignore seasonality, thereby underestimating realized conditions. If human-modified habitats display more seasonal stress than intact habitats, then ignoring seasonality will have particularly important repercussions for conservation. We examined the seasonal dynamics of Amazonian mixed-species flocks, an important species interaction network, across three habitats with increasing human disturbance. We quantified seasonal space use, species richness and attendance, and four ecological network metrics for flocks in primary forest, small forest fragments, and regenerating secondary forest in central Amazonia. Our results indicate that, even in intact, lowland rain forest, mixed-species flocks exhibit seasonal differences. During the dry season, flocks included more species, generally ranged over larger areas, and displayed network structures that were less complex and less cohesive. We speculate that—because most flocking species nest during the dry season, a time of reduced arthropod abundance—flocks are simultaneously constrained by these two competing pressures. Moreover, these seasonal differences were most pronounced in forest fragments and secondary forest, habitats that are less buffered from the changing seasons. Our results suggest that seasonality influences the conservation value of human-modified habitats, raising important questions about how rain forest organisms will cope with an increasingly unstable climate.

Hypotheses about the mechanisms of community assembly suggest that biotic and abiotic filters constrain species establishment through selection on their functional traits. It is unclear how differences in traits influence the niche dimensions of closely related bird species when they coexist in spatiotemporally heterogeneous environments. Further, it is necessary to take into account their participation in mixed-species flocks, social systems that can include both competition and facilitation. For 6 yr, we conducted counts of forest bird species and took measurements of environmental variables along an elevational gradient in the Nanling Mountains, China. To disentangle different deterministic and historical/stochastic processes between flocking and nonflocking bird assemblages, we first compared phylogenetic and functional structure, and community-weighted mean trait values (CWM). We further assessed elevational variations in trait–environment relationships. We found that the flocking and nonflocking bird assemblages were structured by environmental gradients in contrasting ways. The nonflocking assemblage showed a strong change from over-dispersed to clustered community structure with increasing elevations, consistent with the strong selective pressures of a harsh environment (i.e., environmental filtering). The nonflocking assemblage also displayed significant trait–environment relationships in bivariate correlations and multivariate ordination space, including specific morphological and foraging traits that are linked to vegetation characteristics (e.g., short trees at high elevations). By contrast, flocking birds were more resilient to habitat change with elevation, with relatively consistent community membership, and showed fewer trait–environment associations. CWM of traits that are known to be associated with species’ propensity to join mixed-species flocks, including small body size and broad habitat specificity, were linked to the flocking assemblage consistently across the elevational gradient. Collectively, our trait-based analyses provide strong evidence that trait–environment relationships differ between flocking and nonflocking bird assemblages. Besides serving as bellwethers of changing environments, emergent properties of flock systems may increase the resilience of animal communities undergoing environmental change. Mixed-species flocks present an ideal model with which to explore cooccurrence of closely related species, because habitat filtering may be buffered, and the patterns observed are therefore the outcomes of species interactions including both competition and facilitation.

Predation is a strong ecological force that shapes animal communities through natural selection. Recent studies have shown the cascading effects of predation risk on ecosystems through changes in prey behavior. Minimizing predation risk may explain why multiple prey species associate together in space and time. For example, mixed-species flocks that have been widely documented from forest systems, often include birds that eavesdrop on sentinel species (alarm calling heterospecifics). Sentinel species may be pivotal in (1) allowing flocking species to forage in open areas within forests that otherwise incur high predation risk, and (2) influencing flock occurrence (the amount of time species spend with a flock). To test this, we conducted a short-term removal experiment in an Amazonian lowland rainforest to test whether flock habitat use and flock occurrence was influenced by sentinel presence. Antshrikes (genus Thamnomanes) act as sentinels in Amazonian mixed-species flocks by providing alarm calls widely used by other flock members. The alarm calls provide threat information about ambush predators such as hawks and falcons which attack in flight. We quantified home range behavior, the forest vegetation profile used by flocks, and the proportion occurrence of other flocking species, both before and after removal of antshrikes from flocks. We found that when sentinel species were removed, (1) flock members shifted habitat use to lower risk habitats with greater vegetation cover, and (2) species flock occurrence decreased. We conclude that eavesdropping on sentinel species may allow other species to expand their realized niche by allowing them to safely forage in high-risk habitats within the forest. In allowing species to use extended parts of the forest, sentinel species may influence overall biodiversity across a diverse landscape.

1. Non-trophic interactions (or, inter-species associations) play a prominent role in determining community structure and function. Mixed-species bird flocks are networks of non-trophic associations that confer foraging and anti-predator benefits to participant species. Yet, the responses of these interspecific associations to anthropogenic environmental changes are poorly understood. 2. Selective logging is pervasive in the tropics, and can affect associations in mixed-species bird flocks by altering resource availability and/or predation risk, or through the altered abundances of species participating in mixed flocks. Across a gradient of logging intensity, we examined how the number and strength of associations in two different mixed-species flock types responded to logging intensity, while simultaneously controlling statistically for changes in the abundances of species in response to logging. 3. Across the logging gradient, we used network analyses to: (1) quantify the proportion of potentially realizable associations, and (2) measure the strengths of these realized associations. For both these analyses, we used null models to investigate whether changes in the network properties of mixed flocks were simply abundance-driven, or congruent with expectations of how flock properties might be modified by selective logging. 4. In understorey flocks, after controlling statistically for changing abundances of participant species, the proportion of realized associations decreased with increasing logging intensity, whereas mean association strength did not show any relation with logging intensity. In midstorey flocks, both the proportion and mean strength of realized associations increased with increasing logging intensity. 5. Synthesis and applications. By statistically separating abundance and behaviour-mediated effects, we show that interspecific associations in mixed-species bird flocks respond to potential resource and/or predation changes from logging, but that their functional roles persist in logged forest. We show that logged forests can conserve not only community richness, but also function. Thus, these logged forests must be prevented from ongoing conversion into non-forest habitats such as agriculture and plantation.

How species interact with human‐disturbed environments is a central focus of conservation biology. Within disturbed landscapes, regenerating forests have potential to provide habitat for forest species, especially as increasing amounts of primary forest are lost. As secondary forest regenerates beside primary forest, it increases habitat heterogeneity. However, relatively little is known about the influence of habitat heterogeneity on space use. In this study, we analyzed the topography and vertical vegetation structure of regenerating forest, small forest fragments, and undisturbed rainforest in the central Amazon to determine (1) how these structural characteristics influence understory mixed‐species flock space use and (2) how the vegetative preferences of flocks varied across a disturbance gradient. We first used behavioral observations to quantify the vertical foraging niche of flocks and then associated variation in horizontal space use with the three‐dimensional features of forest structure. Surprisingly, we found that flock space use was not consistently associated with any variable, even though available habitat differed both within and across forest types. Overall, the best predictors were elevation and leaf area density within the subcanopy (16–25 m), yet most flock foraging occurred in the midstory (6–15 m). Together, these results indicate that while flocks may have certain habitat preferences, these preferences are flexible or idiosyncratic and do not correspond to a specific vertical profile. For example, flocks spent a disproportionate amount of time in low elevations when available, but not all flocks had access to low‐lying areas within their home ranges. Although other studies show flock size and diversity can be highly sensitive to habitat disturbance, mixed‐species flocks demonstrate remarkable plasticity as a unit, virtually saturating undisturbed and disturbed forest at our site, as long as regeneration has passed a certain threshold.

The value of secondary forest for rain forest species remains an important question for conservation in the 21st century. Here, we describe the spatial behavior of understory mixed-species flocks in a heterogeneous landscape in central Amazonia. Understory mixedspecies flocks represent a diverse, highly organized component of the rich Amazonian avifauna. We recorded movements within 26 flock home ranges in primary forest, secondary forest, interfaces between forest types, and forest fragments. We describe frequency and movement orientation in relation to forest edges, movement patterns and proportion of use between secondary and primary forest, the relation between home range sizes and vegetation height, and home range configuration. Flocks visited only a small portion of forest edges, and showed a tendency for moving parallel to edges next to less-developed secondary forest. Movement patterns in secondary forests did not show significant differences compared to primary forests. Time spent in secondary forests increased in proportion to mean canopy height. Flocks were consistently present in secondary forests where vegetation height averaged over 15 m, but home ranges were nearly twice as large compared to primary forest. Home range limits tended to be aligned with disturbed vegetation, essentially rearranging a territorial configuration normally adjusted by topography. The spatial behavior of this important subset of the Amazonian avifauna shows that secondary forests are tolerated above a certain development threshold, but perceived as suboptimal habitat until canopy height closely matches primary forests.

Raising backyard chickens is an ever-growing hobby in the United States. These flocks can be a substrate for respiratory disease amplification and transmission to commercial facilities. Five hundred fifty-four chickens from 41 backyard flocks were sampled in this study. ELISA kits were used to detect antibodies against avian influenza (AI), infectious laryngotracheitis (ILT), Newcastle disease (ND), infectious bronchitis (IB), Ornithobacterium rhinotracheale (ORT), Mycoplasma gallisepticum (MG), and Mycoplasma synoviae (MS). All visited flock owners answered a biosecurity questionnaire that assessed biosecurity measures. The questionnaire revealed that backyard poultry owners lack simple biosecurity measures such as use of dedicated shoes, their chicken sources are unreliable, and few of them benefit from veterinary oversight. Only one flock had a clear vaccination history against ND and IB. ORT, ND, IB, MS, MG, and ILT were the most seroprevalent in backyard poultry flocks with 97% (41/42), 77.5% (31/40), 75% (30/40), 73% (31/42), 69% (29/42), and 45% (19/42), respectively. The vaccinated flock was not considered in these calculations. When examining the distance between backyard flocks and the nearest commercial poultry facility, ND and MG were significantly more likely to be found in backyard flocks close to (<4 miles) whereas ORT was significantly more likely in backyard chickens located far from (>4 miles) commercial poultry. Birds purchased directly from National Poultry Improvement Plan hatcheries showed a reduced ND, MG, and MS antibody prevalence. Wearing dedicated shoes decreased MS antibody-positive birds. Finally, history of wild bird contact had a clear effect on an increased seroprevalence of NDV and MG. Serological results suggest that backyard poultry flocks have the potential to serve as a reservoir or amplifier for poultry respiratory diseases. The information generated in this project should direct extension efforts toward emphasizing the importance of small flock biosecurity and chick acquisition sources.

Group living has long been viewed as an adaptation to reduce predation risk. Earlier comparative analyses provided support for the hypothesis but typically ignored variation in group size at the local scale and included proxies of predation risk rather than more direct estimates. Here, we related variation in group size at the scale of a study site in various species with the diversity and abundance of local predators. If larger groups provide protection against predators, we expected larger groups to evolve in species facing locally more diverse and abundant predators. We examined this hypothesis in one avian family, the Paridae, which are small arboreal birds that include some of the better studied species in ecology. From the literature, we gathered 275 flock size estimates from 34 species. In a phylogenetic framework and controlling for the potential confounding effect of latitude, we found that flock size increased with predation risk but only in flocks that included more than one species. We suggest that competition sets an upper limit to the size of flocks including conspecifics only. Joining flocks with other species, thus, allows individuals to increase flock size in response to higher predation risk without a substantial increase in competition. Overall, our results based on more direct estimates of predation risk provide further comparative evidence for an association between predation and the evolution of flocking in birds.

Given that both sexes of most parrots learn new vocalizations throughout life and produce them in diverse social contexts, whereas few songbird species combine all these traits, why are parrots not a better model for the evolution of human speech than songbirds? We first note the technical constraints that have limited research on wild parrot communication and then review the discoveries that have accumulated in the last two decades as constraints were overcome. Vocal learning in wild parrots appears unrelated to sexual selection and mate competition but is used by parrot pairs to defend nest sites in ways similar to those of songbirds. Where parrots differ from songbirds is in their specialization on toxic and armored foods, the consequences of this diet on foraging and social dynamics, and the use of learned vocalizations to mediate those dynamics. Parrots thus use learned vocalizations for two quite different functions, only one of which they share with songbirds (and hummingbirds). Interestingly, recent neurobiological studies have shown that parrots have dual cortical pathway nuclei for vocal learning, only one of which is present in songbirds. The parallels between the distributions of functions of vocal learning and brain nuclei suggest future research that should clarify both how and why parrots are more extensive vocal learners than songbirds and whether there are in fact parallels with humans.

Flocking is a typical example of emergent collective behavior, where interactions between individuals produce collective patterns on the large scale. Here we show how a quantitative microscopic theory for directional ordering in a flock can be derived directly from field data. We construct the minimally structured (maximum entropy) model consistent with experimental correlations in large flocks of starlings. The maximum entropy model shows that local, pairwise interactions between birds are sufficient to correctly predict the propagation of order throughout entire flocks of starlings, with no free parameters. We also find that the number of interacting neighbors is independent of flock density, confirming that interactions are ruled by topological rather than metric distance. Finally, by comparing flocks of different sizes, the model correctly accounts for the observed scale invariance of long-range correlations among the fluctuations in flight direction.