Research interests

Evolution of Families in Birds

1) Behavioural Mechanisms

My main line of research focuses on the behavioural mechanisms that facilitate the formation of family groups in birds.  With the help of field experiments, I was able to demonstrate that Siberian jay (Perisoreus infaustus) parents provide their retained offspring with a preferential treatment through enhanced access to food and predator protection when encountering attacking or resting predators (Griesser, 2003; Griesser, 2008; Griesser and Ekman, 2004; Griesser and Ekman, 2005).  These benefits are withheld from unrelated, immigrant group members.  Consequently, retained offspring have a 62% lower odds ratio of being killed by predators than same-aged immigrant group members (Griesser et al., 2006).  I confirmed the pivotal importance of a prolonged investment for the decision of an offspring to remain with its parents by removing fathers.  In response to the experimental removal of fathers, offspring, which had delayed dispersal, dispersed after step-fathers had settled on the territory (Ekman and Griesser, 2002).  Thus, the presence of both parents is crucial for offspring to delay dispersal, since only the presence of both parents prevents unrelated dominants from joining the group and chasing offspring away.

Siberian Jay. © Michael Griesser.

Siberian Jay killed by Goshawk. © Michael Griesser.

2) Role of Life History

In collaboration with Rita Covas I explored the role of life-history on family living (Covas and Griesser 2007). 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 (Griesser 2008). 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 (Griesser et al. 2007). 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, Qi Ma (Department of Mathematics, Uppsala University) Katharine Bowgen, Manuel Soler (University of Granada) and Simone Webber (University of Birmingham).

 
House Sparrow male. © Michael Griesser.
 

Publications

Scientific publications