Michael Griesser, PhD

Contact

E-mail
michael.griesser[AT]ebc.uu.se

Research

My research deals with the evolution of sociality. During the last 10 years of research I tried to figure out why birds live in family groups. A current side-project looks at grouping and group decisions among unrelated individuals.

Siberian Jay. © Michael Griesser.

Evolution of Families in Birds

1) Behavioural Mechanisms
Delayed dispersal is the key to family formation in most kin-group living species. Previous explanations for the evolution of families have focused on dispersal constraints, which fail as a general explanation for family cohesion. My past research explored an alternative explanation, emphasizing the benefits gained through philopatry. Through field experiments, I could confirm that Siberian jay parents provide their philopatric offspring with preferential treatment through enhanced access to food and predator protection. These benefits translate into reduced mortality of philopatric offspring, which have an odds ratio of being killed by predators 62% lower than immigrant group members. Natal philopatry usually involves the suppression of personal reproduction. However, a lower mortality of philopatric offspring can overcome this cost and thus selects for the formation of families and sets the scene for cooperative kin-societies.

Siberian Jay killed by Goshawk.

2) Role of Life History
In collaboration with Rita Covas I explored the role of life-history on family living. Most family-living species are long-lived and recent life-history studies demonstrated that a delayed onset of reproduction can be adaptive in long-lived species. We suggest that delayed dispersal and reproduction might be an adaptive life-history decision rather than ‘the best of a bad job’ and provided a predictive framework for the evolution of families by integrating life-history theory into family formation theory. Longevity favours in a wide range of species a delayed onset of reproduction and gives parents the opportunity of a prolonged investment in offspring, an option which is not available for short-lived species. Yet, parents should only prolong their investment in offspring if this increases offspring survival and outweighs the fitness cost that parents incur, which is only possible under ecological conditions, such as a predictable access to resources. We therefore propose that both life-history and ecological factors play a role in determining the evolution of family living across species.

Evolution of Complex Antipredator Calls

Predation is a powerful agent of natural selection, driving the evolution of antipredator calls. These calls have been shown to communicate predator category and/or predator distance to conspecifics. However, the risk posed by predators depends also on predator behaviour, and the ability of prey to communicate predator behaviour to conspecifics would be a selective advantage reducing their predation risk. Predation by hawks, and to a lesser extent by owls or marten, is substantial and the sole cause of mortality in adult Siberian jays. By using field data and predator-exposure experiments, I showed that jays used antipredator calls for hawks depending on predator behaviour. A playback experiment demonstrated that these prey-to-prey calls were specific to hawk behaviour (perch, prey search, attack) and elicited distinct, situation-specific escape responses. Given that antipredator calls in jays aim at protecting kin group members, consequently lowering their mortality, kin-selected benefits could be an important factor for the evolution of predator-behaviour- specific antipredator calls in such systems.

Effect of Habitat Structure on Fitness Correlates

Forestry has during the last 200 years strongly affected the age structures and stand characteristics that differ from primary forest stands. We used our long-term data on Siberian jays, a long-lived, open-nesting bird species typical to boreal forests of Eurasia to experimentally address the effect of standard forestry practices on fitness correlates. Using a before-after comparison of reproductive data on the level of territories, we demonstrate that standard forestry practices have a strong negative effect on the breeding success of jays. Both partial thinning of territories and partial clearcutting of territories reduces future breeding success by a factor of 0.35. In addition, forestry practices reduce as well territory occupancy. Thus, over 15 years, the productivity of the affected population declined over 50% as a result of territory abandonment and reduced breeding success. Results of previous studies on Siberian Jays suggest that the strong effect of forest thinning on fitness is explained by the fact that most common predators of nests and adults are visually oriented and thus thinning makes prey and nests more visible to predators. The consequences of thinning we observed are likely to apply to a wide range of species that rely on understory to provide visual protection from predators. Thus, these results are important for the development of effective conservation management protocols and for the refinement of thinning practices.

Grouping Decisions and Group Decisions in House Sparrows

Living in groups is widespread in the animal kingdom and has been demonstrated to reduce the predation risk to individuals, which allows them to allocate more time to foraging and thereby increase their survival prospects. Nevertheless, group living is not well understood since the mechanisms that determine group sizes and group dynamics remain unclear. I am currently investigating these questions by combining field experiments with a modelling approach in house sparrows. This work is done in collaboration with David Sumpter, Katharine Bowgen, Manuel Soler and Simone Webber.

House Sparrow male