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Histochemical studies on localisation of lipids, lipase and phosphomonoeste-rases in the crown skin of male baya during non-breeding
and breeding seasons were carried out. The results indicated a high turnover rate for lipid synthesis and its utilisation,
increased acid and alkaline phosphatase activities in the crown skin of breeding male baya as compared to that in non-breeding
season. It is surmised that crown skin of male baya becomes metabolically hyperactive during breeding season aiding processes
such as cell growth and proliferation, keratinization and production of coloured feathers related to breeding. 相似文献
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Six genera of Clad ocera (Diaphanosoma, Daphnia, Ceriodaphnia, Moina, Bosmina, Bosminopsis), each of them usually with only one species were found in Lake D. Helvecio, a natural valley lake located in the eastern part of Brazil. Diurnal migratory movements of the organisms observed in this lake showed a different pattern in different species. Closely related species, which explore the same food source, live in different layers, thus avoiding interspecific competition. The migratory behaviour of the species was studied mainly in relation to temperature and oxygen distribution in the lake. Thus, analyses were made in the summer (January, 1978) when a strong stratification occurs with the establishment of a thermocline and an oxycline. Comparisons were made also with the data obtained in winter (July, 1978), when a complete mixing of water occurs. 相似文献
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RALPH C. MACNALLY 《Austral ecology》1995,20(3):442-454
Abstract Communities of forest and woodland birds are usually studied intensively at only one or a few locations. This provides a perspective that perhaps emphasizes local phenomena at the expense of placing local dynamics in the context of processes operating at the landscape or regional scale. The present paper seeks to redress partially this imbalance by studying the dynamics of individual bird species among several habitat types (all Eucalyptus-dominated forests or woodlands) over the annual cycle. This regional-scale (250km), continental study reveals that species exhibit idiosyncratic dynamics of various kinds: restricted or more ubiquitous occupation of habitats and three forms of seasonal dynamics at the regional scale (resident, migrant and itinerant). By using this classificatory scheme, it becomes evident that the bird communities found in different habitats consist of diverse collections of strategists and that the level of diversity differs among habitat types. The difficulties that many field workers have had in reconciling their observations with community theory most likely reflect the underlying dynamism of bird communities, especially in the temperate regions on continents where seasonal fluxes are pronounced. 相似文献
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Effect of season and photoperiod on the follicle-stimulating hormone receptors in a subtropical bird
Annual changes in and photoperiodic influence oh the weight of gonads, a parameter of gonadal activity, are much smaller in
female birds than in males. Effect of season and photoperiod on the follicle-stimulating hormone receptors in the testis or
ovary was studied using a subtropical weaver finch. The number of follicle-stimulating hormone binding sites per unit testicular
weight showed a peak in the non-breeding phase; while the total number of binding sites per two testes was maximal in the
breeding phase and minimal in the regressive phase. In contrast, seasonal changes in follicle-stimulating hormone binding
sites in the ovary were less marked. Exposure to short-day during the breeding phase induced marked decreases in the numbers
of binding sites per unit testicular weight and per two testes. These numbers markedly increased after transfer to long-day
during the non-breeding phase. However, there was no significant effect of short-day or long-day exposure on follicle-stimulating
hormone binding sites in the ovary. These results suggest that photoperiod is an effective environmental factor in the regulation
of follicle-stimulating hormone receptors in the testis and the effect is manifested by pronounced changes in the testicular
weight during annual breeding cycle. 相似文献
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Six bodies of water in two coastal lagoon systems were investigated in Chiapas State, Mexico between July, 1990 and February, 1991. The size of water bodies ranged from 102.5 to 847.5 ha. Salinity varied seasonally being the lowest in July during the rainy season (1.0) and highest in February (35.8). The waters are hypertrophic with total phosphorus concentrations as high 900 mg m–3.The number of bird species was the highest in February (N = 9 to 23) and the lowest in July (N = 2 to 15). The majority of birds present are resident species of Mexico but several species of northern birds were present in February (e.g. Lesser Scoup, Osprey, Peregrin Falcon).The number of birds observed in the waterbodies varied during the study period being as high as 2800 Cormorants, 2300 White Pelicans and 681 Limpkins, at a particular time, or expressed in terms of units surface area of each lagoon 8.0, 2.7 and 1.9 individuals per hectare respectively. The daily food requirements of White Pelicans at such a high density is about 4.1 kg ha–1 d–1.The hypertrophic state of Cerritos Lagoon allows a sufficient level of production to support such a high food requirement. Considering the limited survey time spent on the lagoons the bird population numbers are probably underestimated. 相似文献