Behavioral and physiological responses to unpredictable changes in environmental conditions are, in part, mediated by glucocorticoids (corticosterone in birds). In polymorphic species, individuals of ...the same sex and age display different heritable melanin-based color morphs, associated with physiological and reproductive parameters and possibly alternative strategies to cope with variation in environmental conditions. We examined whether the role of corticosterone in resolving the trade-off between self-maintenance and reproductive activities covaries with the size of melanin-based spots displayed on the ventral body side of male barn owls. Administration of corticosterone to simulate physiological stress in males revealed pronounced changes in their food-provisioning rates to nestlings compared to control males. Corticosterone-treated males with small eumelanic spots reduced nestling provisioning rates as compared to controls, and also to a greater degree than did corticosterone-treated males with large spots. Large-spotted males generally exhibited lower parental provisioning and appear insensitive to exogenous corticosterone suggesting that the size of the black spots on the breast feathers predicts the ability to cope with stressful situations. The reduced provisioning rate of corticosterone-treated males caused a temporary reduction in nestling growth rates but, did not affect fledgling success. This suggests that moderately elevated corticosterone levels are not inhibitory to current reproduction but rather trigger behavioral responses to maximize lifetime reproductive success.
Genetic evaluation using animal models or pedigree‐based models generally assume only autosomal inheritance. Bayesian animal models provide a flexible framework for genetic evaluation, and we show ...how the model readily can accommodate situations where the trait of interest is influenced by both autosomal and sex‐linked inheritance. This allows for simultaneous calculation of autosomal and sex‐chromosomal additive genetic effects. Inferences were performed using integrated nested Laplace approximations (INLA), a nonsampling‐based Bayesian inference methodology. We provide a detailed description of how to calculate the inverse of the X‐ or Z‐chromosomal additive genetic relationship matrix, needed for inference. The case study of eumelanic spot diameter in a Swiss barn owl (Tyto alba) population shows that this trait is substantially influenced by variation in genes on the Z‐chromosome (σz2=0.2719 and σa2=0.4405). Further, a simulation study for this study system shows that the animal model accounting for both autosomal and sex‐chromosome‐linked inheritance is identifiable, that is, the two effects can be distinguished, and provides accurate inference on the variance components.
A nestling Swiss barn owl (Tyto alba) displaying many large black spots. Photo Alexandre Roulin.
The human brain has accumulated many useful building blocks over its evolutionary history, and the best knowledge of these has often derived from experiments performed in animal species that display ...finely honed abilities. In this article we review a model system at the forefront of investigation into the neural bases of information processing, plasticity, and learning: the barn owl auditory localization pathway. In addition to the broadly applicable principles gleaned from three decades of work in this system, there are good reasons to believe that continued exploration of the owl brain will be invaluable for further advances in understanding of how neuronal networks give rise to behavior.
La lutte contre les rongeurs est souvent un enjeu majeur dans les agroécosystèmes. Nous avons conduit une étude comparative dans des plantations de palmiers à huile dans les provinces de Riau et de ...Bangka en Indonésie. Dans les deux zones, des chouettes ont été introduites pour la lutte contre les rats ; toutefois, à Riau les rats sont maintenus à des niveaux de population acceptables sans recours au raticide, tandis qu’à Bangka les dégâts des rats sont très importants et l’usage de raticide intensif. Nous avons comparé ce deux systèmes en terme d’abondance et/ou de régime alimentaire de deux prédateurs, chouettes et petits carnivores. D’après nos résultats, les petits carnivores sont beaucoup plus abondants dans les plantations à Riau qu’à Bangka, et le chat léopard (Prionailurus bengalensis) est absent à Bangka tandis que cette espèce domine à Riau. Nos résultats suggèrent également que la prédation sur les rats par les chouettes et les petits carnivores serait moindre à Bangka qu’à Riau. D’une manière générale, cette étude confirme l’hypothèse selon laquelle les petits carnivores, notamment les chats léopard, joueraient un rôle important dans la lutte contre les rats en palmeraies. Par ailleurs, nous avons analysé la distribution spatiale des petits carnivores en plantation. Nos résultats suggèrent que, bien que l’habitat palmeraie soit largement utilisé la nuit par certains petits carnivores comme le chat leopard, qui y trouve une abondante ressource alimentaire, la plupart des espèces sont dépendantes de la forêt. Les gestionnaires des palmeraies devraient adapter leurs pratiques, afin de favoriser les petits carnivores dans une perspective de lutte contre les rats.
Rodent pest control is often a major issue in agroecosystems. We conducted a 3-year comparative study (2010-2012) in oil palm plantations in Riau and Bangka provinces, in Indonesia: in both areas barn owls have been introduced for rat control, and were at least as abundant in Bangka plantations than in Riau, but in Riau rat populations have been maintained at an acceptable level without the use of rodenticide, whereas in Bangka intensive rodenticide applications did not prevent high levels of rat damage. We compared these two contrasting systems in terms of predator community (barn owls and small carnivores) abundance and/or diet. We found that small carnivores were much more abundant in Riau plantations than in Bangka, and that the leopard cat (Prionailurus bengalensis) was the dominant species in Riau while absent from Bangka. Our results on diet suggested that rat prey intake from barn owls and from the small carnivore community would be less in Bangka plantations than in Riau. Broadly, our results suggest that small carnivores, notably the leopard cat, play an important role in rodent control. In addition, we investigated spatial distribution of small carnivores within the oil palm habitat. Our results support the hypothesis that, although the oil palm may be habitable for some small carnivore species such as the leopard cat, where they supposedly forage at night, most species still need forest for their survival in oil palm landscapes. Oil palm plantations managers should adapt agricultural practices and land-use to enhance small carnivores, with the view to improve rodent control.
The barn owl uses the interaural time difference (ITD) to determine the azimuth of a sound source. Narrowband ITD-sensitive neurons cannot distinguish a given ITD from those that produce the same ...interaural phase difference (phase ambiguity). Neurons in the external nucleus of the inferior colliculus (ICx) resolve the ambiguity by gathering ITD information across many frequencies, thereby suppressing false responses (side peaks, SP) relative to the true ITD (the main peak, MP) in a response versus ITD curve. This process was quantitatively studied by comparing the ITD curve for a pair of tones presented simultaneously (two-tone curve) to the simple sum (predicted curve) of the individual ITD curves for the same tones presented separately. Sixteen of the 39 neurons tested did not show a significant difference in MP and SP responses between these curves (category I); 14 neurons showed significant SP suppression (category II). During iontophoretic application of bicuculline methiodide, a GABAA antagonist, most (n=7/8) category II neurons lost nonlinear SP suppression and became linear, whereas category I neurons retained linear summation (n=3/3). Thus, the nonlinear cross-frequency interaction of ITD responses in ICx neurons was mediated mostly by GABAergic inhibition, which enhanced SP suppression, and helped resolve phase ambiguity.
Some 4 000 Barn Owl pellets with small mammal remains have been collected over a period of nine years from two locations at the south end of the Langebaan lagoon. Two small samples of bones from ...archaeological sites on the Churchhaven peninsula provide evidence for past mammal occurrences. The remains of small mammals from the owl pellet collections provide an initial list of 18 species that occur within theWest Coast National Park. Subsequent conventional censusing by means of trapping and observational techniques to assess the small and large mammal species diversity of the area were conducted during 1989. This study documents the definite occurrence of 63 mammal species in the park, seven of which are exotics. The presence of a further five species requires confirmation. Interesting insight is gained into how direct censusing and owl pellet analyses augment each other in establishing the presence of small mammal taxa of an area.
In predator-prey foraging games, predators should respond to variations in prey state. The value of energy for the prey changes depending on season. Prey in a low energetic state and/or in a ...reproductive state should invest more in foraging and tolerate higher predation risk. This should make the prey more catchable, and thereby, more preferable to predators. We ask, can predators respond to prey state? How does season and state affect the foraging game from the predator's perspective? By letting owls choose between gerbils whose states we experimentally manipulated, we could demonstrate predator sensitivity to prey state and predator selectivity that otherwise may be obscured by the foraging game. During spring, owls invested more time and attacks in the patch with well-fed gerbils. During summer, owls attacked both patches equally, yet allocated more time to the patch with hungry gerbils. Energetic state per se does not seem to be the basis of owl choice. The owls strongly responded to these subtle differences. In summer, gerbils managed their behavior primarily for survival, and the owls equalized capture opportunities by attacking both patches equally.
Abstract The concentration of circulating glucocorticoids is regulated in response to environmental and endogenous conditions. Total circulating corticosterone, the main glucocorticoid in birds, ...consists of a fraction which is bound to corticosterone-binding globulins (CBG) and a free fraction. There is increasing evidence that the environment modulates free corticosterone levels through varying the concentration of CBG, but experimental evidence is lacking. To test the hypothesis that the regulation of chronic stress in response to endogenous and environmental conditions involves variation in both corticosterone release and CBG capacity, we performed an experiment with barn owl ( Tyto alba ) nestlings in two different years with pronounced differences in environmental conditions and in nestlings experimentally fed ad libitum . In half of the individuals we implanted a corticosterone-releasing pellet to artificially increase corticosterone levels and in the other half we implanted a placebo pellet. We then repeatedly collected blood samples to measure the change in total and free corticosterone levels as well as CBG capacity. The increase in circulating total corticosterone after artificial corticosterone administration varied with environmental conditions and with the food regime of the nestlings. The highest total corticosterone levels were found in nestlings growing up in poor environmental conditions and the lowest in ad libitum fed nestlings. CBG was highest in the year with poor environmental conditions, so that, contrary to total corticosterone, free corticosterone levels were low under poor environmental conditions. When nestlings were fed ad libitum total corticosterone, CBG and free corticosterone did not increase when administering corticosterone. These results suggest that depending on the individual history an animal experienced during development the HPA-axis is regulated differently.
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