Inclusive fitness benefits and dispersal decisions

In cooperative breeding species, breeding pairs generally comprise of one natal and one immigrant parent, thus preserving the social group’s kin structure and facilitating helping by related, non-breeding individuals while guarding against inbreeding. However, in the plural cooperative breeder, the superb starling, both immigrant and resident males as well as immigrant females breed, but never resident females. This sex-specific asymmetry in immigrant and resident breeders leads to low group kin structure and begs the question: why are immigrant males allowed to breed? Using long-term data from 9 groups over 16 years, we investigated factors affecting dispersal decisions, reproductive success, and lifetime fitness in immigrant and resident males.

Publications: Shah, S.S. & D. R. Rubenstein. Prenatal environmental conditions underlie alternative reproductive tactics that drive the formation of a mixed-kin avian society. Science Advances, 8(8): eabk2220. Link.
Collaborators: Dustin R. Rubenstein
Funding and Logistical Support: National Science Foundation, E3B @ Columbia University, and Mpala Research Centre

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Ecological basis of dispersal decisions

The prevailing theory of kin selection cannot explain why 45% of all cooperatively breeding birds form groups in which not all individuals are closely related. Direct benefits such as access to food or breeding opportunities must outweigh the costs of group living for these groups to remain stable in the absence of kin selection. Such benefits vary with environmental factors such as habitat quality, which may lead to variation in immigration of dispersing individuals into groups. Using landscape genomics, we are investigating the relationship between immigration rate and habitat quality to understand the direct benefits driving group living in a cooperatively breeding species with low group relatedness, the superb starling. The results will shed light on direct benefits that make group living adaptive, which may have thus led to the evolution of cooperative breeding despite low group relatedness in a large proportion of cooperative breeders.​

Collaborators: Dustin R. Rubenstein
Funding and Logistical Support: American Ornithological Society, American Museum of Natural History, Sigma Xi Society, National Science Foundation, Mpala Research Centre, and Fuller Evolutionary Biology Program

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Signal evolution based on function

Photo by Joe Welklin (http://www.josephwelklin.com/)

The function of a vocalization can influence its acoustic structure in many ways and ultimately constrain its evolutionary trajectory. We examined the effect of function on signal evolution by comparing calls with three different functions across nine species of fairywrens (Maluridae: Malurus). We found that alarm calls were more similar across species than mobbing or contact calls. Variation in contact calls showed a higher phylogenetic signal than alarm and mobbing calls. Since they are used for conspecific communication, contact calls may experience selection consistent with traits facilitating speciation in Malurus. Conversely, alarm calls may experience directional selection due to environmental constraints on signal propagation and localization. They may converge further to facilitate heterospecific communication of the presence of a threat. Finally, mobbing calls, despite their use in heterospecific communication, may also be used in some conspecific contexts that select for a pattern of divergence. Thus, difference in function can lead to different patterns of signal evolution.

Collaborators: Emma I. Greig and Mike S. Webster​
Funding and Logistical Support: Cornell Lab of Ornithology

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Risk-based alarm calling behavior

Most studies on risk-based variation in alarm calling birds have focused on passerines, perhaps due to the traditional view that passerine vocalizations are more complex. We investigated the presence of a risk-based alarm calling system in a non-passerine, the herring gull. We found that herring gulls change frequency modulation patterns of their alarm calls, generate frequency discontinuities in notes, and increase the rate of calling with increases in perceived threat level. Moreover, conspecifics pay attention to both frequency and time parameters and respond most urgently to playbacks of high-threat calls at a high call rate. A less urgent response to high-threat calls at a low call rate and to low-threat calls at a high call rate suggests that threat urgency information is reinforced by both call type and call rate in herring gulls. This study is one of the first demonstrations of a risk-based alarm calling system in a non-passerine, and was published in the journal Animal Behaviour in 2015.

Publications: Shah, S. S., MacLean, S. A., Greig, E. I. & D. N. Bonter. Risk-based alarm calling in a non-passerine bird. Animal Behaviour, 106: 129-136. Link.
Collaborators: Emma I. Greig, Sarah A. Maclean, and David N. Bonter
Funding and Logistical Support: Cornell Lab of Ornithology (Redheads Fund) & Shoals Marine Lab.

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