Are vocal characteristics related to leadership patterns in mixed‐species bird flocks?

Abstract

What structures the organization of mixed‐species bird flocks, so that some ‘nuclear’ species lead the flocks, and others follow? Previous research has shown that species actively listen to each other, and that leaders are gregarious; such gregarious species tend to make contact calls and hence may be vocally conspicuous. Here we investigated whether vocal characteristics are associated with leadership, using a global dataset of mixed‐species flock studies and recordings from sound archives. We first asked whether leaders are different from following or occasional species in flocks in the proportion of the recordings that contain calls (n = 58 flock studies, 145 species), and especially alarm calls (n = 111 species). We found that leaders tended to have a higher proportion of their vocalizations that were classified as calls than occasional species, and both leaders and following species had a significantly higher proportion of their calls rated as alarms compared to occasional species. Next, we investigated the acoustic characteristics of flock participants’ calls, hypothesizing that leaders would make more calls, and have less silence on the recordings. We also hypothesized that leaders’ calls would be simple acoustically, as contact calls tend to be, and thus similar to each other, as well as being detectable, in being low frequency and with high frequence bandwidth. The analysis (n = 45 species, 169 recordings) found that only one of these predictions was supported: leading species were less often silent than following or occasional species. Unexpectedly, leaders’ calls were less similar to each other than occasional species. The greater amount of information available and the greater variety of that information support the hypothesis that leadership in flocks is related to vocal communication. We highlight the use of sound archives to ask questions about behavioral and community ecology, while acknowledging some limitations of such studies.

Foraging ecology drives social information reliance in an avian eavesdropping community

“…Knowing which species eavesdrop, and the relative value of the social information provided to different eavesdroppers in a network, is fundamental to defining the role of information sharing at the community level (Goodale & Kotagama, 2008;Magrath, Pitcher, & Gardner, 2009;Martínez & Zenil, 2012). Where eavesdropping species rely on antipredator cues provided by heterospecifics, social information provides a mechanism for large-scale facilitation (Contreras & Sieving, 2011;Hetrick & Sieving, 2012;Szymkowiack, 2013) and an important benefit from participation in mixed-species foraging groups (Martínez, Parra, Muellerklein, & Vredenburg, 2018;Pagani-Núñez et al, 2018). There is therefore a need to quantify how reliance on social information may vary among species.…”

Revisiting the ‘nuclear species’ concept: do we really know what we think we know?

“…For example, if we consider ideas related to species traits, only a handful of studies have explicitly examined the link between some species trait and nuclearity (e.g. intraspecific gregariousness: [17]; vocal characteristics: [65]; cooperative breeding: [3]; wing-flash pattern: [8]). Moreover, to our knowledge, Botero [8] is the only study to have experimentally examined the link between a morphological trait—wing flash pattern—and nuclearity.…”

Deforestation alters species interactions

“…Disturbance-adapted species may appear in deforested areas and outcompete forest specialists, and the prevalence of behaviours such as mixed species flocks will depend on the presence of forest specialists, which are found in higher proportions and abundances, conferring functional redundancy, in areas of higher forest cover. [73][74][75][76][77] Indeed, certain forest specialist species in the dataset analysed such as Habia rubica and Thamnomanes caesius are known to be vital to the formation and maintenance of mixed-species flocks, 78,79 and their absence from lower forested areas has previously led to the disintegration of such behaviours. 31,80 Species interactions became more positive at higher forest cover levels across all models.…”