摘要:

The present work is part of an ongoing study on how external and internal factors control the hypothalamus-pituitary-gonadal axis in male great tits (Parus major). In southwest Sweden adult and juvenile male great tits remain absolutely photorefraclory until mid/late September. The site of refractoriness lies in the hypothalamus or some higher neural circuit. Results from the present study suggest that refractoriness is induced by long days affecting the hypolhalamic content and/or secretion of GnRH through a testosterone independent mechanism. Photorefractoriness is both induced and maintained via a testosterone independent mechanism. Short days break refractoriness. From October and onward the postcastration LH response, as well as the photoperiodic LH and testicular responses in intact birds, increased progressively with season, and also with the number of short days to which the birds had been exposed. Maximum seasonal responses were attained in January. Contrary to photorefractory birds, low LH levels in photosensitive great tits are caused by the negative feedback effects of testosterone. This together with the fact that the postcastration response in short day treated birds increased with the number of short days the birds had been exposed to suggest that the reproductive system of the great lit actually is switched on by short days, and that the function ol long days in spring is more to reinforce the photoperiodic drive in order to override the negative feedback effects of testosterone. Furthermore, as the transition to a maximum photoperiodic response is a gradual process that takes several months the situation can be looked upon as a gradual breaking of photorefractoriness, i.e. after breaking absolute refractoriness the great tits are still partly long day refractory. This gradual recovery was found in birds exposed to normally decreasing daylengths (free-living birds) and in those given a constant exposure to short days for a year. The daylength the birds are exposed to determines the lime of onset of gonadal regression and decreased LH secretion. The duration of the entire cycle, as well as the amplitude of the LH/testicular response, is however determined by some other factor. Results indicate that the photoperiodic threshold may change with season. In early and mid autumn there were no increases in testosterone levels during a photoperiodic cycle. In late autumn testosterone levels increased dramatically after about 1 week of exposure to long days, and liters immediately rose when great tits were exposed to long days during late winter. Free-living great tils showed a small but significant increase in gonadal size and circulating levels of LH between December and January. Photorefractory great tits kept on short days lor a year showed similar increases between December and February. Despite the absence of long days testes in these latter birds developed secondary spermatocytes, but no spermalids or sperms. It seems likely that this winter increase is the result of endogenous rhythms. The present results indicate that observed discrepancies between species might in some cases be due to the lact that an experiment has been performed only at one time ol the year.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522990

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This investigation shows that olfactory learning can be involved with food identification. An experimentally induced food preference can be obtained by presenting a scented food to newly hatched workers ofLasius niger(L.) (Hymenoptera Formicidae). Ten colonies were followed from their foundation. From the emergence of the first workers, the colonies were fed with a flavoured (anise) sugar solution (0.5M sucrose) during 1 month. After 3 months of hibernation without food, the colonies were submitted lo a choice test. The preference for the scented food indicates the existence of a “pre-hibcrnal learning” process with long term effects. Older foundations which were exposed to the flavoured food after the 3 months hibernation period preferred the known food, but the preference was less strong than that shown by the first group. Finally, mature workers from adult colonies, submitted to the same treatment, did not respond to the olfactory cues and exhibited no food preference. These results suggest the existence of an early learning period for food odour.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522991

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Overlap among the home ranges of breeding male red-backed shrikesLanius collurioin a valley in Southern Alps (Lombardy, Italy) was correlated with the results ol DNA fingerprinting for six family groups. We found one out of 19 young with the paternity different from that assumed on the basis of behavioural observations. In addition, after the fledging of young we observed some cases of shared care of juveniles involving two out of six pairs observed.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522992

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A population of migratory BuzzardsButeo buteobreeding in the pristine deciduous forests ol the Białowieża National Park (eastern Poland) was studied in 1986–1989. Bleeding densities were 4.5–5.2 pairs/10 km2. Mean clutch size was 2.4 eggs (n = 22), from which 1.9 young hatched, and 1.3 juveniles fledged per breeding pair. Breeding performance of pairs with territories located near the forest edge was positively correlated with the cyclic abundance ofMicrotusspp. in the open river valley and meadows. During the breeding season Buzzards fed primarily on birds (42–75% of prey biomass), rodents (10–26%), and moles (7– 23%). Variation in the proportion of rodents in the diet during May-July was not related lo the changes in eitherMicrotusorClethrionomysandApodemusnumbers. From the bird community living in the Białowieża National Park, Buzzards selectively preyed on medium-sized birds, particularlyTurdus philomelosand woodpeckers, and neglected very numerous small passerines. At least 40% of the birds taken by Buzzards were juveniles or fledglings.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522993

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Female garibaldi damsellishHypsypops rubicundusstrongly prefer to spawn with males guarding early-stage eggs over those guarding empty nests or nests with late-stage eggs. According to the parental investment hypothesis, such female behavior is an adaptive response to male egg-guarding tactics which are dependent on brood size and age, and result in brood size and age-dependent differences in clutch hatching success. In this study, I tested five predictions derived from this hypothesis, along with the underlying assumption that males experience a trade-off between egg guarding and self-maintenance activities. Feeding rates of nesting males declined when males received eggs and remained low until late in the brood-cycle. Thus, males experience a trade-off between egg guarding and feeding. Males nearly always cannibalized the entire brood when they received only a singleclutch, and the probability of cannibalism of last clutches increased with brood age. Males were also more attentive of larger bloods and guarded them more aggressively. These behaviors would result in higher hatching success of eggs deposited among other early-stage eggs.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522994

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The present study investigates the influence of the presence of same-sex litter-mates on the attainment of breeding status by subadult Townsend's voles in natural populations. Males and females were less likely to disappear from their natal area (disperse) and more likely to delay sexual maturation if they had at least one live same-sex litter-mate within the natal home-range when reaching adolescence. Furthermore, among male and female sexually mature subadult voles, the probability of persisting near the natal area and hence recruiting as a breeding resident was higher for those individuals that had a same-sex litter male in their vicinity when maturing sexually. A removal experiment suggested that the increased probability of recruitment of members of family groups was not caused by intrinsic differences between offspring from different litters but results from social interactions between same-sex litter-mates. Dispersal tendency by subadult voles is therefore a highly flexible trait which is influenced by the social environment experienced by individuals.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522995

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

It is suggested that the evolution of polyandry by social hymenopteran queens is caused by colony-level selection, either because polyandry affects the distribution of non-functional diploid males in colonies (the load hypothesis) or because it increases the genetic diversity of the worker force (the diversity hypothesis).

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522996

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Genetic relatedness and the breeding structure of a Japanese paper wasp.Polistes jadwigae, population was studied using electrophoresis ol adults collected from 1985 to 1988. Mean genetic relatedness among female offspring was estimated to be 0.729 when data for 4 years were combined. This value was not significantly different from a hypothetical value (0.75) for the case where one single-mated queen is the mother of all female progeny. No sign of inbreeding was detected. Mating frequency of queens estimated by using the goodness of fit test on Chi-square distribution and the ANOVA method, also suggests that it was most probable that female progeny ofP. jadwigaecolonies were produced by a single queen mated only once.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522997

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

High inbreeding was expected in a very small, apparently isolated colony of llie monogamous passerine Bearded Tit (Panurus biarmicusL.) where it had been shown that juveniles, prior lo the summer molt, form permanent pairs, some of which breed the following year in the study area. Since very early pairing, prior to the dispersal of sibs, might occur between sibs (unless prevented by some mechanism of kin recognition and discrimination), we traced the movements of six sets of sibships for 45 days post-fledging and observed whether any of the birds would pair within this time. Sibs did not disperse more than a few hundred metres from their nests, and tended lo congregate in a preferred area. Four pairs (one between sibs) formed during this period. Contrary to expectation the fingerprints of 13 random adults showed a very low similarity index, typical of large, outbreeding populations. Possible explanations of this unexpected result are considered.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522998

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Canary. The Cornell Bioacoustics Workstation. Version 1.1. Canary 1.1 software for Apple computers and the Canary User's Manual Copyright © 1993, Cornell Laboratory of Ornithology. All right reserved. Price US $ 200.00.

ISSN:0394-9370    

DOI:10.1080/08927014.1994.9522999

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor