A new study examining Great-tailed Grackles has shown that behaviour is key when it comes to the successful range expansions of species.
Great-tailed Grackle has been establishing new populations across North America in the past few decades and the study, published in Peer Community Journal, found that the grackle population on the range edge is more persistent and has more variability in flexibility, and that the species has shifted toward living more in urban and arid environments. In other words, birds on the edge of the range were found to be more likely to push that limit and 'pioneer' beyond it than others, and showed more adaptability when it comes to things like nest-site choices and foraging habits.
Researchers from the Max Planck Institute of Evolutionary Anthropology in Germany, and the University of California Santa Barbara and the University of Rochester in the USA, investigated the role that increased habitat availability might have played in the range of Great-tailed Grackle. They compared the rapidly expanding Great-tailed with its closest relative, Boat-tailed Grackle, which is not expanding its range as quickly.
The study found that the fringe-population Great-tailed Grackles are more flexible in terms of nest-site choice and foraging habits than those in the core population (Clive Daelman).
Based on citizen-science observations of bird occurrences, the researchers found that, between 1979 and 2019, Great-tailed Grackles did not just move into new available habitats that matched their earlier requirements, but they increased their habitat breadth to move into more urban and arid environments.
In contrast, Boat-tailed Grackles only moved their range slightly northwards in response to climate change making these habitats suitable for them.
"These results support the possibility that their behaviour played a role in Great-tailed Grackle's ability to increase habitat breadth," said Corina Logan, a research group leader in the Department of Human Behaviour, Ecology and Culture at the Max Planck Institute of Evolutionary Anthropology, and Gates Cambridge Scholar.
The likely role of behaviour in taking advantage of new habitats led researchers to investigate behaviour in two Great-tailed Grackle populations: a recently established population on the northern edge of the range, and an older population closer to the centre of the range.
The researchers found that the edge population had a wider range of flexibility and was more persistent than the non-edge population.
Being persistent might allow individuals to accidentally find solutions to the challenges they face in their new environments, for example by exposing new food sources. Having more variability of flexibility within a population means that there is a higher chance that at least some individuals in the population will be highly flexible and that other individuals could learn from them, thus facilitating that population's expansion.
Hubbard, J, LeGrande-Rills, C, Logan, C, Lukas, D, Marfori, Z, and McCune, K. 2023. Implementing a rapid geographic range expansion - the role of behavior changes. Peer Community Journal. DOI: 10.24072/pcjournal.320