Pia O. Gabriel

Behavioural syndromes in Steller's jays: the role of time frames in the assessment of behavioural traits.

Behavioural syndromes describe consistent and correlated individual differences in behavioural traits. Quantifying individual differences often requires researchers to capture and hold animals in captivity while short-term behavioural assays are recorded. We compared behavioural responses of adult, territorial Steller’s jays in short- and long-term field assessments of behavioural traits in two ecological contexts, risk taking and exploration. Individuals’ risk taking was similar in short-term and long-term contexts (i.e. alarm calling in the presence of a predator mount and while re-entering a trap, respectively). However, a measure of short-term exploration of a novel object in a feeding context was not related to a long-term index of annual habitat exploration (i.e. travel distance outside home territory). Risk-taking and exploration indices were correlated across ecological contexts, indicating that these traits contributed to a behavioural syndrome in jays. Annual assessments of risk-taking and exploration behaviours were repeatable. Individuals with high scores in risk taking and exploration were more likely to be recaptured in a familiar trap. We conclude that short-term experiments are adequate measures of specific behavioural strategies, but because short-term responses did not necessarily predict long-term annual behaviours in related contexts, expression of behavioural types and associated ecological strategies should be regarded as species and context specific. Long-lived residents are useful study species to overcome sampling biases for traits measured in captivity, because they provide opportunity to evenly sample a population over all personality types, including trap-shy individuals.

REPRODUCTION IN STELLER'S JAYS (CYANOCITTA STELLERI): INDIVIDUAL CHARACTERISTICS AND BEHAVIORAL STRATEGIES

ABSTRACT. We explored the consequences of male and female explorative and risk-taking behaviors that are components of a behavioral syndrome, as well as basic demographic and physical characteristics of three measures of reproductive performance in Stellers Jays (Cyanocitta stelleri). Older individuals of both sexes performed slightly better in measures of annual reproductive performance. Age was also positively correlated within pairs. In some years, males in better winter body condition performed better, whereas higher-performing females were in worse condition. Because winter body condition was negatively correlated within pairs, males in better condition possibly enabled their mates to invest more in reproduction in a given year, losing more body mass than low-performing females. Overall, variation in individual male and female traits, especially behavioral traits, explained little of the variation in annual reproductive performance. That age was identified as the single most consistent factor, which was correlated within pairs, suggests that experience and compatibility may be more important than inherent individual traits. By contrast, when examining reproductive performance over multiple years, less explorative and risk-averse males produced more offspring over the 3-year study period; the direction of relationships of the four behavioral traits in the syndrome was highly consistent. This suggests an advantage for linkage of these traits in a syndrome, supporting the hypothesis that the combination of traits in behavioral syndromes may be a target for selection.

Who’s watching influences caching effort in wild Steller’s jays (Cyanocitta stelleri)

Steller’s jays (Cyanocitta stelleri) often store food and return to retrieve the stored items at a later time. Between caching and consumption, stored food has the potential to be pilfered by conspecific observers. We investigated whether individually marked Steller’s jays in suburban neighborhoods of Arcata, California, USA, adjusted cache concealment effort when in the presence of conspecifics. Both male and female jays traveled the shortest distances to cache when alone, traveled further when a mate was present, and traveled furthest when neighbors from adjacent territories were present. These results suggest that Steller’s jays recognize and respond to social contexts when concealing food items.

Foraging dynamics in Steller's jays: size and viability of cacheable food items

Several species of birds and mammals cache food items, which in harsh conditions may translate into improved survival or reproductive success. Animals may benefit from evaluating the quality of cache items in terms of size, nutrition and storage viability. Steller’s jays, Cyanocitta stelleri, which cache seeds for later consumption, may handle multiple food items with their beak prior to making a selection. By picking items up, individuals may use visual and tactile cues to evaluate size and shell condition. The number of items an individual jay handles is repeatable, reflecting consistent individual-specific foraging behaviours that may differentiate success at selecting high-quality cache items. In this study we quantified population-level preferences for food items based on size and shell integrity, and individual Steller’s jay sampling behaviour when presented with these choices. Using field trials with free-ranging subjects, we quantified sampling frequency in a variety of choice tests and measured individuals’ success at choosing higher-quality items. We found that Steller’s jays selected items of greater weight and items with intact shells, and preferences for these properties were of comparable magnitude. Jays sampled more nuts during choice sets involving cracked and intact shells, resulting in individuals selecting more profitable nuts for caching. These results may suggest that Steller’s jays evaluate cache items based on both current and future expected energetic values, and that sampling behaviour may enable them to choose more valuable forage items.

Steller sex: infidelity and sexual selection in a social Corvid (Cyanocitta stelleri).

Genetic analysis of avian mating systems has revealed that more than 70% of monogamous species show incidence of offspring parentage that does not match the social partner. Extra-pair parentage (EPP) has been linked to a variety of factors, including size and symmetry of ornamental traits, coloration, resource availability, and local conspecific density. We examined how ornamental plumage traits of individual Stellers jays (Cyanocitta stelleri) and territory characteristics influence genetic fidelity of socially monogamous pairs. We used seven highly polymorphic microsatellite markers to assign paternity to 79 offspring, and identified 12 (15.2%) as extra-pair young (EPY). Stellers jays with extra-pair young had significantly lower values of feather brightness and hue, indicating more ultraviolet-blue shifted coloration, and nested in closer proximity to the forest edge than Stellers jays with no detected EPY. Body size, crest height, asymmetry of ornamental crest stripes, as well as vegetative composition of territories and their proximity to supplemental feeders appeared to have little relationship to EPP. These results indicate that extra-pair parentage plays a role in the evolution of secondary sexual characteristics in both sexes, and suggest local density and availability of resources may influence Stellers jay mating dynamics.

Parasites and plumage in Steller's jays: an experimental field test of the parasite-mediated handicap hypothesis

The handicap hypothesis broadly argues that ornamental traits and displays are costly to produce and are a function of individual quality and condition. Consequently, the extent of ornament expression can act as an honest indicator of quality, condition or susceptibility to parasites, and influence the behavior of mates or competitors. We used reflectance spectrometry to quantify non-iridescent, ultraviolet (UV) and blue structurally-based plumage color and character size in relation to individual condition (feather growth rate) and occurrence of disease caused by a parasite infestation (knemidokoptic mange) in wild male Stellers jays (Cyanocitta stelleri). We then attempted to experimentally reduce parasite load prior to molt and quantified the relative change in plumage and condition. Those birds with faster feather growth rates (i.e., in better condition) had lower hues (i.e., reflected shorter wavelengths, displaying a more intense, brilliant UV-blue color), suggesting the possibility of condition or feather growth rate-dependent production of color. We found that UV reflectance (UV chroma) was positively related to the occurrence of disease. We detected no effect of experimental treatment on plumage or condition. In conclusion, our results are suggestive of possible condition-dependent development of structurally-based plumage, and the positive relationship between macro-parasite-caused disease intensity and UV blue plumage color, demonstrated for the first time in this study, did not support the parasite-mediated handicap hypothesis.