Commentary: Mixed-species groups are a route to sociality for solitary species
April 2025
By Hari Sridhar
Konrad Lorenz Institute for Evolution and Cognition Research, Austria.
[email protected]
In their commentary in the first issue of this newsletter, Makuya & Schradin (2025) argue that solitary species are not necessarily 'unsocial', and that they can and do derive fitness benefits from social interactions with conspecifics. Another route to social benefits for solitary species is via heterospecifics. Research on mixed-species groups in a wide variety of taxa, but especially in birds, over the last 100 years (Goodale et al. 2017), suggests that solitary species might be the primary beneficiaries from such groups. For example, in my own research in a forest in India, greater than 80% of the bird species that participated in mixed-species flocks were typically solitary with respect to conspecifics (Sridhar et al. 2013). The obvious question is why are these solitary species choosing to group with heterospecifics instead of conspecifics? One possibility is that these are species in which high levels of intraspecific competition (Beauchamp 2002) or the low availability of conspecifics set limits on intraspecific group sizes. Alternatively, they might be grouping with heterospecifics for services that conspecifics cannot provide. For example, a solitary species that forages in trees, and therefore cannot spot an approaching terrestrial predator, might group with a species foraging on the ground. What makes all of this even more interesting is that the benefactors in mixed-species groups are often social species, i.e. which live in conspecific groups. Therefore, from the point of view of understanding the “social lives of solitary species”, mixed-species groups are a valuable lens, as a stage where solitary and social species come together and interact.
References
Beauchamp, G. (2002). Higher-level evolution of intraspecific flock-feeding in birds. Behavioral Ecology and Sociobiology, 51, 480-487.
Goodale, E., Beauchamp, G., & Ruxton, G. D. (2017). Mixed-species groups of animals: behavior, community structure, and conservation. Academic Press.
Makuya, L. & C. Schradin (2025) Commentary: the need for stringent definitions and why social species are not unsocial. Solo-Times, 1, 8-10.
Sridhar, H., Jordán, F., & Shanker, K. (2013). Species importance in a heterospecific foraging association network. Oikos, 122(9), 1325-1334.
By Hari Sridhar
Konrad Lorenz Institute for Evolution and Cognition Research, Austria.
[email protected]
In their commentary in the first issue of this newsletter, Makuya & Schradin (2025) argue that solitary species are not necessarily 'unsocial', and that they can and do derive fitness benefits from social interactions with conspecifics. Another route to social benefits for solitary species is via heterospecifics. Research on mixed-species groups in a wide variety of taxa, but especially in birds, over the last 100 years (Goodale et al. 2017), suggests that solitary species might be the primary beneficiaries from such groups. For example, in my own research in a forest in India, greater than 80% of the bird species that participated in mixed-species flocks were typically solitary with respect to conspecifics (Sridhar et al. 2013). The obvious question is why are these solitary species choosing to group with heterospecifics instead of conspecifics? One possibility is that these are species in which high levels of intraspecific competition (Beauchamp 2002) or the low availability of conspecifics set limits on intraspecific group sizes. Alternatively, they might be grouping with heterospecifics for services that conspecifics cannot provide. For example, a solitary species that forages in trees, and therefore cannot spot an approaching terrestrial predator, might group with a species foraging on the ground. What makes all of this even more interesting is that the benefactors in mixed-species groups are often social species, i.e. which live in conspecific groups. Therefore, from the point of view of understanding the “social lives of solitary species”, mixed-species groups are a valuable lens, as a stage where solitary and social species come together and interact.
References
Beauchamp, G. (2002). Higher-level evolution of intraspecific flock-feeding in birds. Behavioral Ecology and Sociobiology, 51, 480-487.
Goodale, E., Beauchamp, G., & Ruxton, G. D. (2017). Mixed-species groups of animals: behavior, community structure, and conservation. Academic Press.
Makuya, L. & C. Schradin (2025) Commentary: the need for stringent definitions and why social species are not unsocial. Solo-Times, 1, 8-10.
Sridhar, H., Jordán, F., & Shanker, K. (2013). Species importance in a heterospecific foraging association network. Oikos, 122(9), 1325-1334.
