Mixed-species flock composition matters: interspecific influences on finding novel food in North American parids

Abstract

Individuals of a wide range of species are sensitive to the presence of other species, and can often benefit from associations with other species in mixed-species groups (MSGs) through food-finding or avoiding predation. In an earlier field study, we found that both Carolina chickadees, Poecile carolinensis, and tufted titmice, Baeolphus bicolor , were better able to solve a novel feeder task when their MSGs were more diverse in terms of species composition. Like most studies of MSGs, however, that earlier study did not experimentally manipulate MSG size and composition. We did that manipulation here, providing experimental flocks of chickadees and titmice with three novel feeder tasks in semi-natural aviary environments. We found that successful titmouse flocks generally had a higher proportion of titmice in them, going against the findings of our earlier field study. Conversely, successful chickadee flocks solved one of the novel feeder tasks more quickly with a higher proportion of titmice in them, corroborating the findings of our earlier field study. We now need to assess socio-ecological influences on MSG size and composition, and how those relate to individual behaviour. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

Mixed-species flock sizes and compositions influence flock members’ success in three field experiments with novel feeders

“…Flocks contained an average of 3.89 ± 1.77 (2-8) titmice and 1.39 ± 0.99 (0-4) nuthatches. Mean MSF size was 11.19 ± 3.03 (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) individuals and mean diversity index across flocks was 3.01 ± 0.93 (1.32-4.84). Feeders with the diverse seed mix attracted a median of 4 birds (range 2-7) compared to a median of 3.5 birds (range 2-5) for feeders with the regular seed mix (n 1 = 18, n 2 = 18, U = 87, p = 0.015).…”

“…Both Carolina chickadees ( Poecile carolinensis ) and tufted titmice ( Baeolophus bicolor ) were better able to exploit seed from a novel feeder when in more species-diverse mixed-species flocks with one another and with white-breasted nuthatches ( Sitta carolinensis ) compared to when in less diverse flocks [ 10 ]. Additionally, in captive experimental flocks, chickadees were generally quicker to solve novel feeder tasks when in flocks with larger proportions of titmice [ 11 ]. Likewise, though, titmice were found to solve novel feeder tasks more quickly the higher the proportion of titmice in their flocks [ 11 ].…”

“…Additionally, in captive experimental flocks, chickadees were generally quicker to solve novel feeder tasks when in flocks with larger proportions of titmice [ 11 ]. Likewise, though, titmice were found to solve novel feeder tasks more quickly the higher the proportion of titmice in their flocks [ 11 ]. Titmice appear to be one of the best species at problem solving in a recent comparative study of vocal learning, cognitive processing abilities, and relative brain size [ 12 ].…”

Influence of social and physical environmental variation on antipredator behavior in mixed-species parid flocks

“…Two principal benefits that members in this mixed-species flock system receive are an increased ability to find food and to detect predators [ 21 , 22 ]. Individual behavior in these flocks is often influenced by birds’ calling behavior [ 13 , 23 ]. In particular, the chick-a-dee call produced by chickadees and titmice (and tits in Africa, Asia, and Europe) is a ubiquitous, multi-purpose signal utilized by species in the Paridae and other bird families [ 13 ].…”

“…In particular, the chick-a-dee call produced by chickadees and titmice (and tits in Africa, Asia, and Europe) is a ubiquitous, multi-purpose signal utilized by species in the Paridae and other bird families [ 13 ]. Furthermore, individual behavior–including calling, foraging, and antipredator behavior–is sensitive to the proportions of conspecifics and heterospecifics within these flocks [ 23 , 24 ].…”