Breeding Owls Defecate Strategically

With a four-foot wingspan, the Eurasian eagle owl is a big bird with a big appetite — and a fecal output to match. Yet the owl's body waste does not always go to waste.

New research suggests that breeding eagle owls defecate strategically, using their excrement to erect "No Trespassing" signs within their territories.

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Say It In Song: Researcher Deciphers Meaning Within Bird Communication

To many people, bird song can herald the coming of spring, reveal what kind of bird is perched nearby or be merely an unwelcome early morning intrusion. But to Sandra Vehrencamp, Cornell professor of neurobiology and behavior, bird song is a code from which to glean insights into avian behavior.

Birds use song systems to communicate about mating and reproduction, territorial boundaries, age and even overall health. Vehrencamp studies them to decode which elements convey such essential information. With colleagues in the Bioacoustics Research Program at Cornell's Lab of Ornithology, she studies birds in such natural habitats as Costa Rica, Colombia and Bonaire.

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Dialect use in large assemblies: a study in European starling Sturnus vulgaris roosts

Auteurs: Hausberger, Martine; Bigot, Emmanuel; Clergeau, Philippe
Bron: JOURNAL OF AVIAN BIOLOGY, Volume 39, Number 6, November 2008 , pp. 672-682(11)
Abstract: Dialects may signal social or population identity and increase tolerance within communities. We hypothesized that in European starling Sturnus vulgaris communal roosts, birds coming from the same breeding area, i.e. dialectal zone, might tend to stay together within the roost. Recordings were performed in the colonies, revealed in earlier studies, multiple dialects and small sectors where birds shared the same variants at the different levels.
We also performed recordings in different locations within night roosts. The dialects recorded in the roosts were the same as those recorded at nest sites during the day and they were not distributed randomly within roosts: birds from the same geographical diurnal origin would gather and stay together, either because they arrived together or were attracted to their dialect.
Although our results have to be confirmed by the study of identifiable individuals, we propose original lines of thought on roost structuring and on the role of song dialects.

Sib-sib communication and the risk of prey theft in the barn owl Tyto alba

Auteurs: Roulin, Alexandre; Colliard, Caroline; Russier, Flavien; Fleury, Matthieu; Grandjean, Valentin
Bron: JOURNAL OF AVIAN BIOLOGY, Volume 39, Number 6, November 2008 , pp. 593-598(6)
Abstract: Conflicts among siblings are widespread and their resolution involves complex physical and communication tools. Observations in the barn owl Tyto alba showed that siblings vocally communicate in the absence of parents to negotiate priority of access to the impending food resources that parents will bring. In the present paper, we hypothesize and provide correlative evidence that after a parent brought a food item to their progeny, sibling competition involves vocal sib-sib communication.
A food item takes a long time to be entirely consumed, and hence siblings continue to compete over prey monopolization even after parents gave a food item to a single offspring. When physical competition is pronounced and thereby the risk of prey theft is high, the individual that received a prey item consumes it in a concealed place. Concomitantly, nestlings vocalize intensely probably to indicate their motivation to siblings to not share their food item, since this vocal behaviour was particularly frequent in younger individuals for which the risk of being robbed is higher than in their older siblings.
Furthermore, nestlings consumed more rapidly a food item when their siblings vocalized intensely presumably because the intensity of siblings' vocalizations is associated with a risk of prey theft. Our correlative study suggests that sibling competition favoured the evolution of sib-sib communication under a wide range of situations.

Changing grass height alters foraging site selection by wintering farmland birds

Auteurs: Whittingham, MJ; Devereux, CL
Bron: BASIC AND APPLIED ECOLOGY 9 (6): 779-788 2008
Abstract:
Grassland is a valuable habitat for many farmland bird species, some of which have declined in Europe. Successful management of this habitat is important to benefit these species. Recent studies have suggested little correlation between food abundance and bird use in grasslands instead providing access to food may be crucial. We tested the importance of manipulating sward height (via mowing) on the distribution of wintering birds in agriculturally managed grass fields using two within-field experimental designs. In experiment 1, we investigated the effect of two treatments (mown once and control). In experiment 2. we investigated the effects of four treatments (mown once early. mown once late. mown early and late. and control).

Mown plots supported higher abundances of foraging kestrels, thrushes mid starlings. In contrast meadow pipits and grey herons preferred unmown plots with longer grass. These differences are probably explained by differing anti-predation strategies, increased food abundance for species that prefer above-ground invertebrates (e.g. more food for meadow pipits on longer swards) and increased food accessibility, on short grass swards (e.g. for starling, thrush spp.). There were limited effects of multiple mowing events on plot use suggesting one early winter mowing, treatment may suffice to create favourable conditions for species that prefer shorter swards.
Providing grassland heterogeneity should benefit a range of wintering farmland birds. Although we use mowing to change grass sward height, our findings may also apply at other times of year when livestock grazing may be a more practical solution.

(c) 2007 Published by Elsevier GmbH on behalf of Gesellschaft fur Okologie.

Why Some Bird Species Lay Only One Egg

Why do some species of birds lay only one egg in their nest, while others lay 10 or more?

A global study of the wide variation among birds in this trait, known as the "clutch size," now provides biologists with some answers. The study, published in the current issue of the journal PLoS Biology, combined data on the clutch sizes of 5,290 species of birds with information on the biology and environment of each of these species.

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