Anticipating spring: wild populations of great tits (Parus major) differ in expression of key genes for photoperiodic time measurement.

Measuring day length is critical for timing annual changes in physiology and behavior in many species. Recently, rapid changes in several photoperiodically-controlled genes following exposure to a single long day have been described. Components of this 'first day release' model have so far only been tested in highly domesticated species: quail, sheep, goats and rodents.

Acute stress rapidly decreases plasma testosterone in a free-ranging male songbird: potential site of action and mechanism.

We used a free-ranging, seasonally breeding adult male songbird, the rufous-winged sparrow, Aimophila carpalis, to investigate the effects of acute stress-induced by capture followed by restraint, on the hypothalamo-pituitary-testicular axis. Intra- and interindividual comparisons revealed that males decreased their plasma testosterone (T) by 37-52% in response to acute stress. The decrease occurred within 15 min of capture and persisted for at least another 15 min.

Persistent diel melatonin rhythmicity during the Arctic summer in free-living willow warblers.

Arctic environments are challenging for circadian systems. Around the solstices, the most important zeitgeber, the change between night and day, is reduced to minor fluctuations in light intensities. However, many species including songbirds nonetheless show clear diel activity patterns.

Ambient temperature effects on photo induced gonadal cycles and hormonal secretion patterns in Great Tits from three different breeding latitudes.

The present study determines how populations of Great Tits (Parus major) breeding in southern, mid and northern European latitudes have adjusted their reproductive endocrinology to differences in the ambient temperature during the gonadal cycle. A study based on long-term breeding data, using the Colwell predictability model, showed that the start of the breeding season has a high predictability ( approximately 0.8-0.

Chronic administration of leptin in Asian Blue Quail.

It is well known that leptin has the capacity to reduce food intake, cause body weight loss, and increase energy expenditure in several vertebrate species. In this study, we investigated the effects of chronically elevated leptin levels on behavior and physiology of Asian Blue Quail (Coturnix chinensis). Fifteen male quail were treated with chicken leptin dissolved in phosphate-buffered saline (PBS) via subcutaneously inserted osmotic pumps that released approximately 1 microg/g body weight/day during a 14-day period.

Large-scale geographical variation confirms that climate change causes birds to lay earlier.

Advances in the phenology of organisms are often attributed to climate change, but alternatively, may reflect a publication bias towards advances and may be caused by environmental factors unrelated to climate change. Both factors are investigated using the breeding dates of 25 long-term studied populations of Ficedula flycatchers across Europe. Trends in spring temperature varied markedly between study sites, and across populations the advancement of laying date was stronger in areas where the spring temperatures increased more, giving support to the theory that climate change causally affects breeding date advancement.

Territorial aggression, circulating levels of testosterone, and brain aromatase activity in free-living pied flycatchers.

Testosterone (T) is a critical endocrine factor for the activation of many aspects of reproductive behavior in vertebrates. Castration completely eliminates the display of aggressive and sexual behaviors that are restored to intact level by a treatment with exogenous T. There is usually a tight correlation between the temporal changes in plasma T and the frequency of reproductive behaviors during the annual cycle.

Leptin depresses food intake in great tits (Parus major).

Food availability for wild organisms typically varies both in time and space, requiring a mechanism that regulates the storage of excess energy and makes it possible to use stores during energy shortfall. Leptin, a protein hormone encoded by an obesity gene, has been suggested to be the signal mediator for this flux of energy. In a controlled laboratory experiment on caged great tits (Parus major) we evaluated the effect of leptin on food intake and behaviour.

Variation of lymphoid activity in the spleen of a migratory bird, the pied flycatcher (Ficedula hypoleuca; Aves, passeriformes).

The size and microscopic structure of the spleen of the migratory pied flycatcher (Ficedula hypoleuca) show marked changes during the reproductive cycle. Upon the spring return to their northern breeding sites, the birds have a small spleen with little lymphoid activity and a poorly developed red pulp. During the breeding period the volume of red and white pulp increases, the number and distinctness of lymphoid follicles (germinal centres) in the white pulp increase, and groups of cells with intensely basophilic cytoplasm, probably B cells (plasma cells), appear.