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.

Sight of a predator can stimulate a corticosterone response in the great tit (Parus major).

The corticosterone response to the sight of a natural predator was investigated in free-living and captive great tits (Parus major). Free-living great tits responded to the sight of a stuffed, slowly moving Tengmalm's owl, a major predator of great tits, with warning calls and a change in behaviour around a feeder. Great tits returned to the feeder within a few minutes and began to approach the owl, and there was no increase in plasma corticosterone levels in birds sampled 30-50 min after they first saw the owl.

Variation within and between birds in corticosterone responses of great tits (Parus major).

The present study investigated inter- and intraindividual variation of the stress response (in terms of plasma levels of corticosterone) to handling in birds. Individual captive great tits (Parus major) were exposed to a standardised capture and handling protocol three times at about 2-week intervals. Mean plasma corticosterone levels were low (<5 ng/ml) when the birds were first sampled and increased in all birds 10 min after handling (mean levels on each sampling occasion 14 to 22 ng/ml).

Testosterone, ticks and travels: a test of the immunocompetence-handicap hypothesis in free-ranging male sand lizards.

The immunocompetence-handicap hypothesis suggests that androgen-dependent male characters constitute honest signals of mate and/or rival quality because of the imposed costs through immune suppression associated with elevated testosterone levels. We demonstrate in a field experiment that male sand lizards (Lacerta agilis) exposed to elevated testosterone suffered from increased mass loss and tick load compared to control males. Although the first of these two results could be due to an elevated basal metabolic rate from increased plasma testosterone levels, the increased parasite load was statistically independent of the loss in body condition and is likely to be due to compromised immune function.

The effects of testosterone on a viral infection in greenfinches (Carduelis chloris): an experimental test of the immunocompetence-handicap hypothesis.

The immunocompetence-handicap hypothesis suggests that the honesty of quality signals could be guaranteed if testosterone (T) suppresses immune function while enhancing male ornaments. In addition, it has been proposed that the cost of enhancing ornaments should be highest for males with small ornaments. Recently, the assertion that T causes obligate immunosuppression has been questioned.

Distribution of aromatase activity in the brain and peripheral tissues of passerine and nonpasserine avian species.

Many behavioral effects of testosterone on hypothalamic and limbic brain areas are mediated by the action, at the cellular level, of estrogens derived from local testosterone aromatization. Aromatase activity and cells containing the aromatase protein and mRNA have accordingly been identified in the brain areas involved in the control of behavior. The presence of an unusually high level of aromatase activity has been detected in the telencephalon of one songbird species, the zebra finch (Taeniopygia guttata), and it is suspected that this high telencephalic aromatase may be a specific feature of songbirds but this idea is supported only by few experimental data.

Effect of season and photoperiod on FSH in male great tits.

The present study investigated (1) the photoperiodic threshold for an increase in FSH and LH secretion in male great tits (Parus major) from south Sweden and (2) seasonal changes in FSH secretion patterns in short day (SD; 8 L:16 D) and long day (LD; 20 L:4 D) exposed great tits. When fully photosensitive great tits were exposed to a simulated vernal increase in day lengths plasma levels of FSH started to rise at a shorter day length (10.5 h) than did LH (11 h).

Territorial behaviour and hormones of pied flycatchers in optimal and suboptimal habitats.

Since pied flycatchers, Ficedula hypoleuca, breed at higher densities in deciduous forests than in coniferous forests, competition for territories is likely to be greater in the former, optimal habitat. I tested the hypotheses that males in a deciduous forest defend their newly established territories more intensely and have higher plasma levels of testosterone than males in a suboptimal coniferous forest. In the deciduous forest, breeding density was higher, egg laying started earlier and more fledglings were produced.

Behavioural and hormonal responses of the pied flycatcher to environmental stressors.

I investigated the effects of high plasma levels of corticosterone in male pied flycatchers, Ficedula hypoleuca, during the period of territorial establishment and the nestling period. In a second experiment males were exposed to a territorial intruder, a great spotted woodpecker model and a weasel model during the nest-building and nestling periods and their behavioural and hormonal reactions studied. Males were also exposed to handling stress (hormonal study) during these periods.

Neuroanatomical distribution and variations across the reproductive cycle of aromatase activity and aromatase-immunoreactive cells in the pied flycatcher (Ficedula hypoleuca).

The anatomical distribution and seasonal variations in aromatase activity and in the number of aromatase-immunoreactive cells were studied in the brain of free-living male pied flycatchers (Ficedula hypoleuca). A high aromatase activity was detected in the telencephalon and diencephalon but low to negligible levels were present in the optic lobes, cerebellum, and brain stem. In the diencephalon, most aromatase-immunoreactive cells were confined to three nuclei implicated in the control of reproductive behaviors: the medial preoptic nucleus, the nucleus of the stria terminalis, and the ventromedial nucleus of the hypothalamus.

Seasonal changes in follicle-stimulating hormone in free-living great tits.

We describe the annual cycle in plasma levels of FSH in free-living male and female great tits from southwest Sweden. Both juvenile (here defined as first-time breeders or birds <1 year old) and adult great tits, of both sexes, showed clear annual cycles with three periods of elevated FSH levels: period from territorial establishment till end of breeding (mid-March to June), October (a time when the birds break photorefractoriness), and winter (January-February). Significant differences between ages and between sexes occurred only during March and April (period of territorial establishment and gonadal recrudescens).

Natural and photoperiodically induced changes in plasma prolactin levels in male great tits.

Plasma levels of prolactin showed a pronounced annual cycle in free-living male great tits (Parus major). During the period from August to April, levels were very low. Prolactin levels started to increase in mid-April, and maximal levels were reached in June.

The development of the hypothalamic-pituitary-gonadal axis in juvenile great tits.

The development of the hypolamic-pituitary-gonadal axis in free-living nestling great tits (Parus major) was studied from the day of hatching until about 40 days of age. The hypothalamic content of GnRH was low during the entire nestling period, although a significant increase was noted between 6 and 9 days of age. Thereafter there was no further increase.

Influence of the opposite sex on photoperiodically induced LH and gonadal cycles in willow tit (Parus montanus).

In early January photosensitive willow tits (Parus montanus) were transferred from natural to long days (20L;4D). The study included three groups of birds: one group consisted of pairs (one male and one female kept together in a cage), a second group consisted of males, and a third group included only females. Birds from the separate groups could neither see nor hear each other.

Low temperatures affect the photoperiodically induced LH and testicular cycles differently in closely related species of tits (Parus spp.).

Photosensitive great tits (Parus major) and willow tits (P. montanus) were exposed to long days (20L:4D) under three different temperature conditions (4+, +10, and +20 degrees C) in early winter. The two species showed significant differences in their LH and testicular reaction patterns to low temperatures.

Photoperiodic adaptation to breeding at different latitudes in great tits.

The photoperiodic responses in testicular growth and plasma levels of LH in nonmigratory great tits from Tromsö, Norway (69 degrees 40'N), Göteborg, Sweden (57 degrees 42'N), and Milano, Italy (45 degrees 26'N) were compared under the same lighting conditions. Male great tits, collected during midwinter, were transferred to Göteborg, and shifted from an 8-hr day in early January to a lighting regime in which day length was increased by 1/2 hr per week for 16 weeks. Control birds (only from Sweden) were kept on a 8L:16D light regime during the entire study.