Relation of Light to Bird Migration and Developmental Changes

Rowan, William

doi:10.1016/b978-0-12-550150-7.50008-4

Cited by 22 publications

(25 citation statements)

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“…The general role of light in regulating the annual development of the gonads of temperate zone birds is well known and countless confirmatory experiments have been performed since Rowan's (1925) original discoveries (recent reviews have been given by Farner 1959a, gmme 1960, van Tienhoven 1961. But while impressive experimental data are available they refer almost entirely to north temperate zone passerines; even though there exist numerous species, suitable for experimentation, which judged by their natural breeding ecology could display new and different features and so repay study.…”

Section: Introductionmentioning

confidence: 99%

PHOTORESPONSES OF THE WOODPIGEON COLUMBA PALUMBUS IN RELATION TO THE BREEDING SEASON

Lofts

Murton

Westwood

1967

Ibis

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Summary The gametogenetic response following photo‐stimulation was tested in Woodpigeons under controlled laboratory and aviary conditions. Subjects were wild‐caught adult or first‐winter birds or were hand‐reared from wild‐taken nestlings. The natural seasonal gonad cycle is described and experiments were related to this cycle. Gonad recrudescence could be initiated in adults with regressed organs by exposure to summer photoperiods, while the normal vernal recrudescence could be prevented if birds were artificially kept on short (winter) daylengths. Thus Woodpigeons could be stimulated towards reproductive condition at seasons when the gonads of wild‐living birds remained inactive, viz. late September to mid‐February. Juvenile males were unresponsive to extra photo‐stimulation until they were about six months old. This meant that some spermatogonial division could be procured in a few individuals in late February, but juveniles were not very noticeably affected by an extended photoperiod until mid‐late March. This is the time when juveniles first begin gametogenetic development in the wild, though spermatogenesis normally accelerates in April after which time the rate of gonad development is constant. First‐winter females were judged to resemble males in their photoperiodic responses but the sample examined was small. The results confirm that the natural gonad cycle in the Woodpigeon is controlled (via gonadotrophic hormones) by seasonal changes in daylength. More important is the finding that the species appears to possess no post‐nuptial refractory period. Thus, at the end of the breeding season in September birds kept on summer daylengths were maintained in full reproductive condition until December. The testes of controls placed on winter daylengths regressed within one month, but they were immediately responsive to a summer daylength which stimulated spermatogenesis within a month. The discussion argues that the avian refractory period is not a necessary period for gonad rehabihtation and reorganization and that it has not evolved as a fixed period serving to time the breeding season; views which until now have been current. Instead, it functions only as a safety mechanism, preventing unseasonal reproduction in those species for which natural selection favours seasonal breeding. In such species the evolution of sensitivity to a particular daylength could result in breeding taking place at the wrong time, for example spring responding species might also respond in the autumn. Because natural selection permits Woodpigeons to remain in breeding condition from March until September, without disadvantage, a direct response to natural daylength can regulate the cycle, and there is no need for a period of pituitary refractoriness. It is not known if some pigeons have lost the refractory period or whether they never possessed one.

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Section: Introductionmentioning

confidence: 99%

PHOTORESPONSES OF THE WOODPIGEON COLUMBA PALUMBUS IN RELATION TO THE BREEDING SEASON

Lofts

Murton

Westwood

1967

Ibis

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“…Daylength and temperature are rapidly reducing, and it will not be until the following spring that the necessary stimuli are again encountered. However, artificially increased daylengths will, as the pioneer experiments of Rowan (1925Rowan ( , 1926Rowan ( , 1929 so beautifully demonstrated, initiate gonadal recovery in such birds.…”

Section: Introductionmentioning

confidence: 99%

Photoperiodism and the testicular refractory period in the mallard

Lofts

Coombs²

1965

Proceedings of the Zoological Society of London

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The effects of winter daylengths on the duration of pituitary refractoriness to photostimulation are described. The mallard, as do probably all wild avian species, enters a postnuptial refractory period during which the gonads display no gametogenesis and the anterior pituitary becomes seasonally unresponsive to photostimulation so far as gonadotrophin secretion is concerned. This phase lasts about three months and is an important synchronizer of the breeding cycles. Refractory specimens kept under a summer daylength of 16.5 hours remain unresponsive to photostimulation at a time when birds in their natural environment are emerging from their refractory period. When, however, such birds are subjected to a period of eight hours daylengths there is a shortening of the refractory phase and they display a gonadotrophic response to photostimulation. There is some indication that a phase of winter daylengths is not, however, a necessary pre‐requisite for birds to be capable of emerging from the refractory period and recovering some degree of spermatogenetic activity. Thus, even in some specimens kept under the long photoperiods there were spermatogonia multiplications occurring when the experiment was terminated.

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“…Tramway noise increases intermittently every time a tram passes by but between these noise peaks short fractions of time would allow acoustic communication between the birds. Since Rowan's first experiments on photoperiod and avian reproduction (Rowan 1925), numerous studies report a stimulating effect of experimentally increased day length or LAN on gonad recrudescence (e.g., Farner and Wilson 1957;Dominoni et al 2013a). This seems to contrast with our results, but we do not exclude an advancing effect of LAN on the gonadal growth of the blackbirds in our study.…”

Section: Discussionmentioning

confidence: 99%

Seasonal and urban effects on the endocrinology of a wild passerine

Russ

Reitemeier

Weißmann

et al. 2015

Ecology and Evolution

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In order to maximize their fitness, organisms in seasonal environments rely on external cues to optimally time their life‐history stages. One of the most important zeitgeber to time reproduction is the photoperiod, but further environmental cues are assessed to fine‐tune reproduction due to year‐to‐year variation in environmental conditions. However, in urbanized environments, the pervasive artificial light at night has altered the natural signal of light and darkness. Accordingly, artificial light at night was repeatedly shown to affect avian reproductive physiology and to advance seasonal reproduction in birds. However, these experiments were mainly conducted in the absence of further environmental cues to facilitate the investigation of the mechanisms which are still poorly understood. Here, we investigate whether the endocrine system of free‐ranging European blackbirds (Turdus merula) correlates with the amount of artificial light at night along a rural to urban gradient while the birds still encounter complementary environmental cues including seasonal variation in day length and temperature. Testosterone and estrone were assessed as metabolites in fecal samples and corticosterone in blood from mist‐netted blackbirds. We demonstrate that seasonal fluctuations in abiotic factors, individual conditions, but also light at night affect the reproductive and stress physiology of wild European blackbirds. Elevated artificial night light intensities were significantly positively correlated with corticosterone and negatively with female estrone levels. No effects of artificial light were found for testosterone levels. Our results suggest that female blackbirds in particular perceive even low levels of artificial light at night as a weak but chronic stressor that interacts with the hypothalamic‐pituitary‐gonadal axis and leads to a reduced secretion of reproductive hormones. These findings point out that the impacts of light pollution are diverse and we only slowly disentangle its multiple effects on physiology, ecology, and biodiversity.

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Relation of Light to Bird Migration and Developmental Changes

Cited by 22 publications

References 0 publications

PHOTORESPONSES OF THE WOODPIGEON COLUMBA PALUMBUS IN RELATION TO THE BREEDING SEASON

PHOTORESPONSES OF THE WOODPIGEON COLUMBA PALUMBUS IN RELATION TO THE BREEDING SEASON

Photoperiodism and the testicular refractory period in the mallard

Seasonal and urban effects on the endocrinology of a wild passerine

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