Life history strategies and risk-taking behavior in great tit (Parus major)

Abstract

Abstract

Individuals within species often show a consistent differences in their risk-taking behavior. I investigated whether intra-specific variation in risk-taking behavior is adaptive, i.e. if it stems from the life history strategy differences between individuals. As a result of life history trade-offs, individuals vary in their investment into survival and reproduction, such that some individuals put more emphasis on future fitness while other individuals put more emphasis on current fitness. Individuals who put more emphasis on future fitness are expected to carry higher future assets and individuals who put more emphasis on current fitness are expected to carry lower future assets. According to the asset protection principle, individuals having higher future assets should behave cautiously to protect those high assets they carry, and vice versa for individuals having lower future assets. I tested this by measuring risk-taking behavior in a wild great tit (Parus major) population, and by investigating if between individual variation in risk-taking behavior is related to between individual variation in reproductive investment. I used the following parameters as indicators of reproductive investment: a) clutch size, b) number of fledglings raised. I also investigated the effect of the brood size manipulations on risk-taking behavior to see if experimental manipulations of reproductive investment affects risk-taking behavior. The findings indicate that birds adjust their risk-taking behavior according to the assets they carry. Birds having smaller clutches and birds raising experimentally reduced broods adopt a less risky strategy to protect their high future assets. Both natural (clutch size) and experimental (brood size manipulations) data-sets were consistent with predictions from the asset protection principle, providing a strong indication that this is the most likely explanation for between individual variation in risk-taking behavior in this system.

Popular science summary:

Life-history strategies and risk-taking behavior in great tit

Individuals within a species often differ consistently in their behavior, a phenomenon that is known as personality. One of the behaviors individuals vary consistently is risk-taking behavior. Risk-taking behavior can be defined as the actions that increase the resources for the individual with the cost of increased mortality due to predation risk. In this study I was interested if there is an adaptive/evolutionary explanation behind the between-individual differences in risk-taking behavior in great tit (Parus major).

According to the life-history theory, individuals should adjust their risk-taking behavior to their residual reproductive value, i.e. their expected future fitness (future survival and reproduction). As a result of life-history trade-offs, individuals that invest a lot on reproduction pay the cost of this high reproductive investment by lower future reproductive success or lower future survival (they are expected to carry lower future assets). Individuals that carry lower future assets are expected to behave more risky as they do not have much to lose anyway; on the contrary, individuals that carry higher future assets are expected to behave less risky as they have to survive to realize those high future assets they carry. In this study I investigated this link between reproductive investment and risk-taking behavior, with the prediction that individuals investing more on current reproduction by laying bigger clutches or raising more young should involve in more risky actions than the individuals investing less on current reproduction. I also investigated the effect of the brood size manipulations (experimentally changing the number of young in the nests) on risk-taking behavior.

The project was conducted between January-March 2011 with wild great tit population in Seewiesen, Bavaria, Munich. Risk-taking behavior was measured by manipulating the predation risk perceived by the birds by using a stuffed sparrowhawk model near the feeders in the forest plots. ‘Latency’ to return to feed from the feeder after the sparrowhawk and the ´feeding rates after/before the sparrowhawk’ were used as indices for risk-taking behavior.

Results seem to support my hypothesis: birds that invested less on reproduction (by laying smaller clutches and by experimentally given reduced broods) are the ones who behave the least risky, which indicates the high future assets they carry makes the ‘less risky’ behavior the optimal one (As they have to survive to the next spring to realize those high future assets). This study to my knowledge was unique to show a long-term effect of reproductive investment on risk-taking behavior, so the physiological mechanisms that mediate these reproductive costs from spring to the next winter should be investigated. In addition, in the line of these promising results, replicate studies are necessary to increase the sample size and to offer a mechanism to explain the between-individual variation in risk-taking behavior.

Advisors: Jan-Åke Nilsson (Lund University), Marion Nicolaus (Max Planck Institute for Ornithology), Kimberley Mathot (Max Planck Institute for Ornithology)
Master´s Degree Project in Animal Ecology, 30 credits, 2011
Lund University, Department of Biology
Max Planck Institute for Ornithology, Behavioral Ecology and Evolutionary Genetics

• author: Kabadayi, Can
• supervisor: Jan-Åke Nilsson; Marion Nicolaus; Kimberley Mathot
• organization: Degree Projects in Biology
• course: BIOM32 20111
• year: 2011
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 2213088
• date added to LUP: 2011-11-22 16:22:38
• date last changed: 2013-03-26 14:22:36