Thesis (M.S.)--Ohio State University. / Bibliography: leaves 98-104. Available online via OhioLINK's ETD Center

Recent changes in agricultural practice have reduced the diversity of habitats for a number of bird species, including the European Starling Sturnus vulgaris. I investigated the distribution of a starling population on farmland, and related this distribution to the availability of suitable habitats by studying the foraging behaviour of individual birds. I observed a preference of the overwintering flock for established pasture fields, particularly those which were closer to the central roost, which had shorter grass and which provided feeding areas further from hedges. I also demonstrated the role of leatherjacket Tipula paludosa availabilities in influencing the starlings' choice of feeding site. These prey were shown experimentally to be preferred over earthworms Lumbricus spp. which were the other main type of invertebrate prey available. I was unable to detect any systematic temporal pattern of habitat use which could have been linked to an appropriate theoretical framework (e.g. Ideal Free Distribution). I investigated the impact of starling foraging on prey availability by observing the behaviour of captive starlings allowed to forage in small enclosures. These experiments indicated that, at the level of foraging pressure expected in natural flocks, there was no significant resource depression during a single flock feeding visit to any one site. Furthermore I proposed that the extent of resource depression during the winter was insufficient to cause a shift in the birds' choice of foraging habitat over this period. The apparent lack of effects of resource depression raised the question of why starlings did not feed in the most preferred fields all the time. Further enclosure experiments investigated how an individual's foraging success might be affected by feeding with conspecifics. I found no evidence for enhancement or depression of foraging success as a result of feeding where another bird had just previously foraged, and little evidence for an effect of feeding in the presence of two other birds, despite changes in vigilance and time spent fighting. A possibly greater heterogeneity of these effects when in the natural flock situation was considered in relation to the observed flock departures. These and other effects (e.g. sampling the environment) were discussed as possible causes for the observed flock movements between fields. A final enclosure experiment investigated the impact of starling foraging on prey availability during the breeding season and demonstrated significant resource depression in a preferred field over the chick-feeding period. I then discussed starling foraging and the availability of suitable habitats in relation to the documented population decline of this species.

Agelaius phoeniceus (red-winged blackbird), Quiscalus quiscula (common grackle), and Sturnus vulgaris (European starling) are three of the most abundant bird species found in North America, and along with Euphagus carolinus (rusty blackbird) and Euphagus cyanocephalus (Brewer’s blackbird), make up a significant proportion of the avian population. Population trends of these four blackbird species and European starlings (EUST)were analyzed from the Christmas Bird Count (CBC) data collected between 1988 and 2008. Population analyses were conducted using linear mixed-effect regressions from the Lmer package of Program R. This approach was effective in modeling the population trends of widespread species with large populations. However, it was not as effective in modeling species with smaller populations and distributions. Only RWBL had significant change in population during the study period, showing a positive increase in mean count number of approximately 2.4% each year. Habitat selection showed some parallels among species.

One basic requisite for rationality is that choices are consistent across situations. Animals commonly violate rationality premises as evidenced, for example, by context-dependent choices, and such apparent irrationalities stand as paradoxes that instigate re-examination of some assumptions in behaviour ecological modelling. The goal of the present thesis was to study the psychological mechanisms underlying apparent irrationalities in order to assess the functional implications of general processes of valuation and choice. A common thread through the different studies is the hypothesis that most animal 'irrationalities' are due to misinterpretation of what the optimum would be in natural circumstances, and hence of the maximised currency in the theoretical predictions. I believe that the trait that may have been of paramount influence in many organisms' selective history was the ability to learn about the predictability of events and their biological value, and that this is implemented in an overriding force of associative learning mechanisms. In chapters 2 and 3, I present evidence of context-dependent foraging choices in European starlings, Sturnus vulgaris, in the laboratory, and I implement a version of the Rescorla- Wagner learning model to account for both present data and apparent irrationalities reported by other authors. In chapter 4, I test the notion that context dependence may in fact be adaptive when animals face sequential choices, namely when they have to decide whether to take a prey item or to skip it in order to search for better alternatives. In chapter 5, I explore the functional implications of starlings' relative responding to incentives during an unexpected shortfall in reinforcement, and I also examine the extent to which information about the new environmental status helps them avoid energetic and time costs commonly seen in uninformed individuals. Last, in chapter 6, I present a brief summary of the main discussions considered and conclusions reached along this thesis.

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Over the past several decades, there has been growing concern among the public and scientific community regarding adverse health effects resulting from exposure to natural and synthetic compounds that act as endocrine disrupters. The structural similarity of many of these compounds to natural hormones and receptors, as well as their ubiquity in the environment, can result in the potential for interference with the endocrine system of wildlife and humans. Much of the research examining the adverse effects of wildlife exposure to endocrine disrupting chemicals (EDCs) has focused on effects on reproduction or short-term changes in hormone physiology. However, organisms exposed to low levels of EDCs at early life stages could also be susceptible to developmental effects, including neurological and other physiological changes affecting later life stages. In birds, migration can be an important component of the annual life cycle and it can be vulnerable to disruption given that it is under endogenous hormonal and neurological control. Previous studies have shown that developmental exposure of birds to thyroid hormone disruptors, such as polychlorinated biphenyls (PCBs), have resulted in reduced hatching success, lower growth rates, teratogenicity, impaired development, and immunotoxicity. In this thesis, I aimed to supplement what is currently known regarding the effects of developmental exposure to low levels of a mixture of endocrine disrupting chemicals in songbirds, as well as further investigate the latent consequences of such an exposure on migratory life stages. I initially investigated the potential physiological and developmental effects of early exposure to Aroclor 1254, a PCB mixture, in two passerine songbird species: European starlings (Sturnus vulgaris) and red-winged blackbirds (Agelaius phoeniceus) during the critical nestling period. In 2011, European starlings and red-winged blackbirds were orally administered Aroclor 1254 over the period of nestling development, which was repeated in 2012 with only European starlings. For both years, morphological parameters (body mass, tarsus, wing-chord and bill-lengths) were measured daily and plasma thyroid hormones were measured. Additional measurements of wing chord and tarsus length fluctuating asymmetry (FA) were taken in the second year, to further assess contaminant-induced alterations in developmental stability. I found that treatment with environmentally-relevant levels of Aroclor 1254 caused increasing liver residues above the controls but did not result in overt effects on morphological growth parameters during the nestling period in either starlings or red-winged blackbirds. However, we did observe significant differences in 2012 starling’s wing chord FA at day 10 and 13, and tarsus length FA between all treatment groups and controls, indicating the potential for PCB-induced stress. Nestling thyroid hormone profiles (T3) sampled throughout the nestling period supported developmental changes but did not reveal any differences among treatment groups. Starlings were subsequently reared in captivity and further tested during a simulated autumn migration. Migratory activity and orientation were tested using Emlen funnel trials over 6 consecutive weeks. Across treatment groups, we found a significant increase in mass, fat, and feather moult, and decreasing plasma thyroid hormones over time. At 12L:12D, control birds showed a peak in activity and a directional preference for 155.95° (South-southeast), while high-dosed birds did not. High-dosed birds showed a delayed directional preference for 197.48° (South-southwest) under 10L:14D, concomitant with apparent delays in moult. These findings link alterations in avian migratory behaviour to contaminant-specific mechanisms. Exposure to a ubiquitous environmental endocrine disruptor exerted only subtle short-term effects during the period of exposure but importantly, latent effects may be far more relevant for individual fitness. We discuss how the impacts of exposure during early stages of development were not significant for short-term nest success, but can still give rise to longer time-scale effects that are potentially relevant for survival and population stability for migratory birds.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 157-190).

Cooperatively breeding societies, in which one or more non-parental individuals (“alloparents”) care for young alongside the parents, show considerable variation in social structure. Traditionally, such societies have been thought to comprise small, kin-based family groups where offspring from previous broods delay dispersal and help raise closely-related offspring to gain indirect fitness benefits when independent breeding opportunities are unavailable or yield lower fitness outcomes. However, genetic evidence is increasingly revealing cooperatively breeding species whose social groups comprise unrelated individuals as co-breeders or alloparents or both (for e.g., 45% of all avian cooperative breeders). Such social groups exhibit complexity in social structure such as large group size, multiple breeders, and low and varied group kin structure. To understand why such complex societies form and how are they maintained when the opportunity to gain indirect benefits via kin selection is low and variable, I investigated the direct and indirect benefits driving a key demographic process, dispersal, and the resulting variation in group social structure on the individual, group, and population levels in an obligate, avian cooperative breeder, the superb starling (Lamprotornis superbus). I used a combination of long-term, individual-level data spanning 15 years from nine groups monitored at the Mpala Research Centre in Kenya and fine-scale genetic and environmental data sampled across 22 social groups that included the long-term study population. In Chapter 1, I show that (i) dispersal decisions in superb starling males are driven by temporal environmental variation experienced by their parents pre-laying, (ii) both dispersal and philopatry result in equivalent lifetime inclusive fitness outcomes, and (iii) oscillating selection due to high temporal variability in the environment likely maintains the two alternative dispersal tactics, resulting in the formation of mixed-kin groups. In Chapter 2, I show that (i) immigrants are vital to the stability of superb starling social groups in light of low and variable offspring recruitment in a harsh, unpredictable environment, (ii) plural breeding likely arises as a result of reproductive concessions provided by group members as joining incentives to recruit immigrants, and (iii) despite smaller groups providing more reproductive concessions, immigrants gain higher fitness in larger social groups and thus prefer to immigrate into larger groups which are found in higher-quality territories. Finally, in Chapter 3, I find genetic signatures of directional dispersal from social groups in low- to high-quality territories across an environmental gradient which likely generates considerable within-population variation in group social structure. Overall, my dissertation underscores the importance of direct benefits derived from group augmentation in the formation and maintenance of cooperative social groups with a complex social structure in a harsh and unpredictable environment.

Decision making is a framework we impose on a vast universe of possible behaviors to better understand the advantages and disadvantages of acting in different ways. Decisions under uncertainty are of particular interest because stochasticity is a feature of environments both today and throughout evolutionary history. As a result, we might expect decision makers (DMs) to have evolved mechanisms to handle variability. In this dissertation, I examine common decision processes in several model species: European starlings (Sturnus vulgaris), Banded tetras (Astyanax fasciatus) and humans (Homo sapiens). The broad range of approaches discussed include currencies DMs are expected to maximize (Risk Sensitivity Theory, Expected Utility), the currencies DMs do maximize (e.g. long versus short term rate maximizing models), the representation of outcomes in memory (Scalar Expectancy Theory) as well as explicit choice mechanisms (Sequential Choice Model). The first section of this thesis discusses responses to risk, offering humans and starlings choices between options which deliver certain or variable outcomes. Starlings demonstrate sensitivity to changes in the probability of variable outcomes and strong support for local rate maximization. Humans appear similarly sensitive to their own accuracy when task difficulty is varied. When the DM’s affective state was manipulated, neither humans nor starlings exhibit changes in risk preferences, but the effectiveness of these manipulations used could not be confirmed. Another topic of inquiry is the effect of the DM’s state at the time of valuation learning. State dependent valuation learning is demonstrated for the first time in a fish species, but Within Trial Contrast is not observed in starlings. Lastly, two experiments find strong support for the Sequential Choice Model, a promising new model of the mechanism of choice. Taken together, these experiments offer a glimpse into shared decision processes, but leave open questions about the mechanisms through which value is acquired.

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