Ibis 

About: Ibis is an academic journal published by Wiley-Blackwell. The journal publishes majorly in the area(s): Population & Nest. It has an ISSN identifier of 0019-1019. Over the lifetime, 6635 publications have been published receiving 167276 citations. The journal is also known as: Threskiornithinae.

The timing of birds‘ breeding seasons

Abstract: Summary Examination of survival rdtes of nestlings and fledglings of some species show that there is a strong tendency for those young which are hatched earliest in the season to have the greatest chance of surviving to breed. Since natural selection so strongly favours parents who leave many surviving young, the question arises as to why other birds breed later than the date at which they could most successfully raise their young. It is suggested that the food supply for the breeding females immediately prior to the breeding season may limit their ability to form eggs and the females may thus not be able to lay at the time which would result in young being in the nest at the best time for raising them, but as soon after this time as the female is able to produce her eggs. Not all species are likely to be prevented, by food shortage, from breeding at the best time for raising young and the groups of birds most likely to be affected are discussed.

The importance of certain assemblages of birds as “information‐centres” for food‐finding

Abstract: Summary Evidence is presented to support the hypothesis that communal roosts, breeding colonies and certain other bird assemblages have been evolved primarily for the efficient exploitation of unevenly-distributed food sources by serving as “information-centres”. Predation-pressure is regarded as being the most important factor “shaping” the assemblages. The shaping involves the choice of inaccessible or otherwise safe sites, optimum dispersal, mutual awareness of attack and joint defensive tactics, and serves to minimise the vulnerability to predation which would otherwise result when birds mass together in conspicuous, and often predictable centres.

Patterns of growth in birds

Abstract: Summary Parameters used to characterize the course of growth are described, and calculated growth parameters are presented for 105 species of birds of many taxonomic groups from a wide range of geographical localities. Growth parameters are found to exhibit as much as 20% variation within a species with respect to geographic locality and time of the nesting season. There is also considerable local variation, irrespective of season and locality, which is related to nutrition and perhaps to an inherited variability. The application of curve-fitting as a method of analysing intraspecific variation is discussed briefly, and the importance of comparative growth studies is emphasized. Growth patterns are correlated with other parameters of the life-history to evaluate the extent of diversity in the course of growth. Low rates of growth and prolonged growth periods occur primarily in species large for their families and in oceanic species. In most others, high rates of growth are maintained for longer periods of time. The shape of the growth curve is not related to the mode of development (i.e. whether precocial or altricial). Overall relative, or weight-specific growth rates, as measured by the constants of fitted growth equations, are most highly correlated with the adult body size of the species, changing as the -0–278 power of adult body weight. Smaller variations in the rate of growth appear to be correlated with differences in nesting success; open-nesting passerines grow faster than hole-nesting species of a similar size. Growth rate is further correlated with brood size. Oceanic species with single egg clutches and tropical land-birds with small clutches have low growth rates. The asymptote of the growth curve of the young (in relation to the adult weight) is related to the foraging behaviour of the adults. Aerial feeders generally have high asymptotes while those of ground feeding species are usually below adult weight. These differences are related to the need in the former for well-developed flight at the time of fledging. The diversity of growth patterns is related to evolutionary trends which are the result of (1) selective forces acting at stages of the life-history cycle other than development, (2) factors which affect the survival of offspring during the growth period, and (3) adjustments made to balance the energy budget of the family group. The last trend is discussed in detail in relation to the correlations found in the analysis. Two hypotheses are presented. Firstly, in species which cannot gather enough food to support even one young at a normal growth rate, the pace of development is reduced to decrease the energetic requirements of the young. Secondly, in species with small clutches, where adjustments to feeding capacities are not readily made by changing brood size, growth rate may be adjusted to accomplish this. The lack of critical energetic data to test these hypotheses is emphasized as a major deficiency in our understanding of the breeding biology of birds.

The regulation of numbers of tropical oceanic birds

Abstract: SUMMARY The ways in which the numbers of tropical sea-birds might be limited are considered; it is argued that food is the only factor likely to be generally effective in limiting numbers, but it seems improbable that food shortage could exert a density-dependent control of the mortality of the birds outside the breeding season. Wynne-Edwards' hypothesis that colonies of sea-birds are able to keep their own numbers below the level at which food shortage would become acute, primarily by exerting control on the output of young, is rejected as unproven and improbable. It is suggested that colonies of tropical oceanic birds deplete the food in the waters round them, and that as the populations increase competition for food becomes more intense, and relatively fewer adults succeed in raising chicks. This would provide a density-dependent control of the output of young and could regulate the numbers of the birds. The peculiarities of long-lived sea-birds (e.g. clutches of one, long fledging periods, deferred maturity) which Wynne-Edwards suggests are adaptations evolved in order to lower the reproductive rate until it balances the mortality, apparently could not be evolved as such; they are more probably adaptations enabling the birds sometimes to raise single chicks in spite of competition for food that makes it impossible to raise more than one. It is considered that variation in the age of first breeding provides an important supplement to variation in reproductive success in regulating the numbers of long-lived tropical sea-birds. The possible applications of this hypothesis to sea-birds breeding in higher latitudes are briefly considered, as are its implications in relation to conservation and exploitation of populations of sea-birds.