Seasonal changes in mixed‐species bird flocks and antipredator information

Abstract

Animals acquire information produced by other species to reduce uncertainty and avoid predators. Mixed‐species flocks (MSFs) of birds are ubiquitous in forest ecosystems and structured, in part, around interspecific information transfer, with “nuclear” species providing information that other species eavesdrop on. We hypothesized that in a seasonal tropical forest, the amount of information produced by birds about predation would be dynamic and particularly would decrease inside MSFs when the nuclear species leave MSFs to breed. We obtained baseline information on MSF encounter rate and species composition along established sampling routes over 9 months near the Sino‐Vietnamese border. We also conducted three experiments to quantify information produced by different species in response to typical predator encounters, including a moving predator stimulus presented inside of MSFs, and a stationary predator model presented both inside and outside of MSFs. MSFs were much less frequent in the breeding season with fewer individuals of the nuclear species, David's Fulvetta (Alcippe davidi), participating, though the diversity of other species remained stable. Fulvettas were the dominant producer of alarm‐related information both to the moving and stationary stimuli in MSFs and were also among the most active mobbers to stimuli presented outside of MSFs. In the breeding season, they tended to call less to the moving stimulus, and substantially fewer individuals responded to the in‐flock stationary stimulus. Other species increased their own information production at stationary predator stimuli (inside and outside of MSFs) during the breeding season, perhaps due to their increased investment in offspring during this time. Yet even during the breeding season, David's Fulvetta remained the highest producer of information about predators in MSFs. Hence, while we show that information production in MSFs can be somewhat dynamic, we describe a continually asymmetric communication system, in which a nuclear species is important to the whole community.

Mixed‐species bird flocks enhance the benefits of group aggregation by minimizing variation in body mass while maximizing variation in diet

“…predator scape). Indeed, information transfer allows the optimal trait variation, given that predator escape behavior (Goodale et al 2010, Jiang et al 2020) and ecological adjustment (Sridhar and Guttal 2018) are maximized among individuals of similar size. Interestingly, individuals from solitary species might greatly benefit by forming close associations in interspecific groups.…”

Seasonal dynamics of flock interaction networks across a human‐modified landscape in lowland Amazonian rain forest

“…In the central Amazon, the nuclear species, Thamnomanes caesius , is critical for flock cohesion and exerts a disproportionate influence on flock space use and time budgets. Although tropical flocks may respond idiosyncratically to the breeding season of their nuclear species (Jayarathna et al 2013, Jiang et al 2020), we repeatedly watched as T. caesius led the entire flock to its nest, which it proceeded to build for upwards of 44 minutes, while the remainder of the flock stalled out and waited silently nearby (see a similar account in Develey and Peres [2000] for flocks led by Habia rubica ). Therefore, we would predict that constraints of nesting for both T. caesius and the various constituent species would shrink home range sizes, decrease attendance rates and species richness, and weaken flock networks.…”

Do golden snub-nosed monkeys use deceptive alarm calls during competition for food?

“…Several hypotheses have been proposed, such as those based on kin selection and individual selection. 17 , 18 , 19 , 20 …”