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Carry-Over Effects across Life Stages in Red Kites $\textit{Milvus milvus}$


Catitti, Benedetta. Carry-Over Effects across Life Stages in Red Kites $\textit{Milvus milvus}$. 2024, University of Zurich, Faculty of Science.

Abstract

The study of behavioural differences among individuals, as well as the mechanisms behind it, are increasingly recognized to be crucial for the understanding of demography of animal populations. Throughout an individual’s life stages, external and internal conditions interact, influencing the development of distinct phenotypes. It is the concatenation of these individual-environment interactions that ultimately determines unique fitness outcomes and shapes the population structure, but studies adopting such broad, mechanistic approaches are lacking, probably due to the challenge of collecting detailed longitudinal data. In this thesis, I aimed to build such a mechanistic framework using an extensive large-scale GPS-tracking dataset of red kites (Milvus milvus). Specifically, I first investigated in detail the behavioural dynamics of red kites during development. Then, through the manipulation of food provisioning, I examined how the natal environment can affect the emergence of sociality and further investigated their subsequent survival effects.

In Chapter I, I delved into the dynamics of sibling aggression in the nest to better understand how they can shape among individual differences later in life. By adopting a null-model approach, I showed that red kite nestlings strategically adjust how to direct their aggression depending on the daily changes in food provisioning, and that these adjustments associate with a skewed food allocation towards senior siblings when food is scarce, but allow for higher intake of youngest siblings, and thus catch-up growth, when conditions improve. These food-driven aggression patterns can have implications for both the individual physical development and the acquisition of dominant-subordinate personalities.

In Chapter II, I investigated how early-life conditions affect the emergence of social phenotypes in the early dispersal phase and tested for their underlying spatial mechanisms. To do so, I combined a supplementary feeding experiment during growth with social network analysis and analysis of movement behaviour. I found that last-hatched chicks—the least competitive— had the fewest number of peer encounters after fledging. However, if food supplemented, they had more encounters than all other groups. These outcomes were driven by differential space use, with less competitive individuals naturally spreading out into marginal areas, and food supplemented individuals clustering in central foraging areas. These results highlight that early-life conditions can have significant effects on individual behaviour beyond independence, with potentially far-reaching consequences on the social and spatial structure of animal populations.

In Chapter III, I delved into the drivers of individual differences in winter communal roosting, a behaviour with distinct social and spatial implications. I hypothesised that the variation in communal roost attendance should be largely attributable to cost-benefit trade-offs associated with age, breeding status and sex. Through a food placing experiment, I showed that birds that joined communal roosts approached ephemeral feeding sites significantly more and had a larger home range size compared to those that roosted solitarily, suggesting improved food detection of communally roosting birds. The propensity of roosting decreased with age, whereas it remained low in females and decreased in both sexes once they started breeding. This overall suggests that communal roosting provides benefits in terms of foraging, but that the net benefit of roosting changes with experience and life-history stage and differs between sexes.

To conclude the thesis, in Chapter IV I investigated the fitness consequences of the nataldriven social phenotypes identified in Chapter II. I tested for associations between the intensity of social interaction (as a proxy for sociality) and survival in the four years following their first winter migration. Contrary to our expectations, sociality was linked to decreased annual survival. Sociality was further associated with an increased mortality risk due to collisions at roads and railways, and with a tendency to fly in closer proximity to roads. These results suggest that social individuals of this facultative scavenging species may show increased preference for scavenging—a risky but costeffective form of foraging. Altogether, it appears that behavioural phenotypes arising from favourable early-life conditions can negatively influence survival, disrupting the expected chain of “silver spoon” effects as a result of anthropogenic changes and thus, representing an ecological trap.

With this thesis, I uncover new pathways through which behavioural differences arise among individuals as a function of their early-life conditions and how they further interact with the rapid anthropogenic landscape changes to affect survival. Collectively, my work advocates for the need to establish mechanistic pathways considering individual-environment interactions over time. This approach is crucial for gaining a better understanding of how individual behavioural differences emerge and translate to population-level outcome.

Abstract

The study of behavioural differences among individuals, as well as the mechanisms behind it, are increasingly recognized to be crucial for the understanding of demography of animal populations. Throughout an individual’s life stages, external and internal conditions interact, influencing the development of distinct phenotypes. It is the concatenation of these individual-environment interactions that ultimately determines unique fitness outcomes and shapes the population structure, but studies adopting such broad, mechanistic approaches are lacking, probably due to the challenge of collecting detailed longitudinal data. In this thesis, I aimed to build such a mechanistic framework using an extensive large-scale GPS-tracking dataset of red kites (Milvus milvus). Specifically, I first investigated in detail the behavioural dynamics of red kites during development. Then, through the manipulation of food provisioning, I examined how the natal environment can affect the emergence of sociality and further investigated their subsequent survival effects.

In Chapter I, I delved into the dynamics of sibling aggression in the nest to better understand how they can shape among individual differences later in life. By adopting a null-model approach, I showed that red kite nestlings strategically adjust how to direct their aggression depending on the daily changes in food provisioning, and that these adjustments associate with a skewed food allocation towards senior siblings when food is scarce, but allow for higher intake of youngest siblings, and thus catch-up growth, when conditions improve. These food-driven aggression patterns can have implications for both the individual physical development and the acquisition of dominant-subordinate personalities.

In Chapter II, I investigated how early-life conditions affect the emergence of social phenotypes in the early dispersal phase and tested for their underlying spatial mechanisms. To do so, I combined a supplementary feeding experiment during growth with social network analysis and analysis of movement behaviour. I found that last-hatched chicks—the least competitive— had the fewest number of peer encounters after fledging. However, if food supplemented, they had more encounters than all other groups. These outcomes were driven by differential space use, with less competitive individuals naturally spreading out into marginal areas, and food supplemented individuals clustering in central foraging areas. These results highlight that early-life conditions can have significant effects on individual behaviour beyond independence, with potentially far-reaching consequences on the social and spatial structure of animal populations.

In Chapter III, I delved into the drivers of individual differences in winter communal roosting, a behaviour with distinct social and spatial implications. I hypothesised that the variation in communal roost attendance should be largely attributable to cost-benefit trade-offs associated with age, breeding status and sex. Through a food placing experiment, I showed that birds that joined communal roosts approached ephemeral feeding sites significantly more and had a larger home range size compared to those that roosted solitarily, suggesting improved food detection of communally roosting birds. The propensity of roosting decreased with age, whereas it remained low in females and decreased in both sexes once they started breeding. This overall suggests that communal roosting provides benefits in terms of foraging, but that the net benefit of roosting changes with experience and life-history stage and differs between sexes.

To conclude the thesis, in Chapter IV I investigated the fitness consequences of the nataldriven social phenotypes identified in Chapter II. I tested for associations between the intensity of social interaction (as a proxy for sociality) and survival in the four years following their first winter migration. Contrary to our expectations, sociality was linked to decreased annual survival. Sociality was further associated with an increased mortality risk due to collisions at roads and railways, and with a tendency to fly in closer proximity to roads. These results suggest that social individuals of this facultative scavenging species may show increased preference for scavenging—a risky but costeffective form of foraging. Altogether, it appears that behavioural phenotypes arising from favourable early-life conditions can negatively influence survival, disrupting the expected chain of “silver spoon” effects as a result of anthropogenic changes and thus, representing an ecological trap.

With this thesis, I uncover new pathways through which behavioural differences arise among individuals as a function of their early-life conditions and how they further interact with the rapid anthropogenic landscape changes to affect survival. Collectively, my work advocates for the need to establish mechanistic pathways considering individual-environment interactions over time. This approach is crucial for gaining a better understanding of how individual behavioural differences emerge and translate to population-level outcome.

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Additional indexing

Item Type:Dissertation (monographical)
Referees:Ozgul Seyfi Arpat, Grüebler Martin U, Jenni-Eiermann Susanne, Jenni Lukas
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
UZH Dissertations
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Language:English
Place of Publication:Zürich
Date:20 February 2024
Deposited On:20 Feb 2024 11:20
Last Modified:21 May 2024 20:45
Number of Pages:157
OA Status:Green
  • Content: Published Version
  • Language: English