摘要:

In England juvenile Willow warblers undergo premigratory lipid deposition in August. Prior to this there is a moult of the juvenile plumage which results in a reduction in both the glycogen content and the wet weight of the pectoralis muscles, the latter reflecting a decrease in the lipid‐free dry weight. Muscle lipid levels are apparently unaffected by this moult. The decrease in the weight of the lipid‐free dry fraction of the body extends also to components other than these muscles at this time. A correlation between the wet weight and the glycogen content of the pectoralis muscles suggests that cold stress may be the cause of the low glycogen levels found in the middle of the moult; part of this increased demand for thermogenesis may be due to lower body insulation brought about by feather loss during the moult. The muscle “hypertrophy” found in the premigratory period is simply a return to pre‐moult weights.The uniformity of total body weights during and after the moult indicates that at the end of this moult the water fraction of the body decreases in weight. The pectoralis muscles of juvenile Willow warblers are not fully grown on fledging; these unmoulted birds may also have higher body lipid levels than during the follow

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1975.tb01404.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Allometric coefficients are calculated for 27 cranial and 39 postcranial measurements of a growth series ofAlligator mississipiensisthat spans a size range of an order of magnitude. Developmental patterns are quite‐well canalized, as expressed in coefficients of variation of 8 to 10 for isometric variables. A multivariate expression of allometry is discovered using principal components analysis. A number of allometric coefficients have expression in known aspects of the life history ofAlligator.Negative allometry of limb lengths and limb proportions shows an ontogenetic decrease in importance of the limbs throughout life, and observations show large animals to be more dependent on water than small ones. Isometry of skull length with respect to body length represents an adaptation to ever‐increasing size of prey items as body size increases. Positive allometry of snout length and size of the upper temporal fenestrae finds parallel in the structure of the highly aquatic gav

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1975.tb01405.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Variation in eight morphological variables was analysed for the three New Zealand species of oystercatchers,Haematopus ostralegus finschi, Martens,H. unicolor, Forster, andH. chathamensis, Hartert. Within species, significant size variation was detected among age classes and between the sexes, making it necessary to use measurements only from adults and to treat the sexes separately in ensuing taxonomic comparisons. Analysis of morphological variation in hybridizing forms ofH. unicolorsuggests that gene exchange between the parental black and pied phases is extensive. Univariate and multivariate statistical analyses isolated three phenetic entities, consistent with three species as proposed in recent classification.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1975.tb01406.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Metabolic rate and body temperature in nestling Blue tits and House sparrows were measured in broods of different size and age. Surface‐volume ratio effects were found in both poikilothermic and homoiothermic Blue tits at ambients of 15°C but not at 20°C. The possibility of incipient hyperthermia amongst young nestlings maintaining sub‐adult body temperatures is discussed. For the House sparrows heat retention by the nest was of greater importance than the surface‐volume effect. Differences in nest structure between the two species are described and related to the thermal requirements of nestlings in large as against small

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1975.tb01407.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The paper presents data on group size frequencies and mean group sizes in 11 species of ungulates and, for seven of them, more detailed information on the composition of groups in Tsavo East National Park, Kenya. In several species, mean group size was higher in a part of the study area with more open vegetation. No significant seasonal variations in mean group size were found, except in waterbuck which concentrated markedly in one location during the dry season. Minor local or seasonal variations in the proportions and/or sizes of different group types were evident in most species. In general, grouping patterns were consistent with the type of social organization found in other areas for the species concerned. Frequencies and types of interspecific associations, and the possible factors underlying their formation, are also discussed.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1975.tb01408.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

It has been shown that heterotypically conditioned media (Het. C.M.) produced by lettuce fed snails maintained at various densities can influence the allometric growth and the rates of specific growth, ingestion, egestion, assimilation and heart beat of isolated assay snails. The growth rate of the assay snails was enhanced by increasing the density of snails producing the Het. C.M. to an optimum threshold of one snail per 100 ml. Further increases in density were followed by a decline in their growth rate. The higher growth achieved by the assay snails in the optimum treatment can be attributed to the fact that their specific growth rates over the first three weeks of the experiment were higher than those of snails in other treatments.Ingestion and assimilation correlated well with specific growth rates. Percentage assimilation values are high, ranging from 78.4 to 89.6%. The onset of reproductive activity is followed by a dramatic decline from approximately 26 % to 5 % in the gross efficiency of utilization of food for somatic growth.Snails not receiving Het. C.M. from the outer tanks have a relatively higher ratio of specific growth rate in weight to length than was the case with snails in the other treatments. The heart beat rates of snails in the Het. C.M. produced by snails at densities of 80 to 160 snails per 41 are significantly lower than those of snails at other densities. The possible causation and adaptive significance of these effects are discussed.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1975.tb01409.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The Grey seal breeding assembly on North Rona was studied throughout autumn 1972. Weekly censuses provided data on birth rate and mortality. It is estimated that 1736 pups were born in 1972. This is about 500 less than the mean production estimate for this assembly during the period 1959–71, possibly a result of disturbance of the breeding site by the expedition. About 600 of the pups died before putting to sea. The mean date of birth and the duration of the pupping season agree closely with earlier work on North Rona, although the mean daily birth rate curve is somewhat irregular, perhaps because there was an unusually dry spell of weather at a critical time in the pupping season. An improved estimate of mortality at this assembly showed a relationship with pup density similar to that observed at the Fame Islands. Techniques for estimating pup production (and consequently total population), though not reliable for determining absolute values, are useful for indicating trends and they suggest a stable population of 8000–9000 animals at North Rona. Such estimates might be improved by the use of better methods of aerial photogra

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1975.tb01410.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY