Volume 19, Issue 4
October 1994, pages 353-509
pp 353-353 October 1994
pp 355-368 October 1994
Free-living birds must satisfy fluctuating nutrient requirements in diverse and varying environments. Ingesting nutritionally complementary foods may be the most effective means by which wild birds match nutrient ingestion and nutrient needs. Dietary complementation may occur fortuitously when foods chosen in response to non-nutritive factors (e.g. competition, predation risk, food colour), or on the basis of energy density, also fulfill specific nutrient needs (passive dietary complementation). In some environments, especially during productive phases (e.g. reproduction), free-living birds may rely on nutrient appetites to ensure their choice of foods satisfies their nutrient needs (active dietary complementation). Meeting nutrient needs through dietary complementation can be facilitated, complicated, or impeded by any of several environmental or organism determinants of food choice. Nutrient appetites, exogenous food stores, and endogenous nutrient stores are three organismal determinants that are probably the most important in facilitating dietary complementation.
pp 369-380 October 1994
Two systems of bird-crop interactions were studied to explain the between- and the within-field variation in the foraging pattern of bird pests in agro-ecosystems. Weaverbirds and munias select rice fields with greater vegetation complexity and not based on the resource status. Within a selected area the concentration of feeding birds was greater close to vegetation cover and decreased non-linearly with increase in distance. Certain structural features and earhead characters of rice plants predisposed particular varieties for intense grain predation by birds. In the parakeet-sunflower system the extent of damage among plants within a field was closely linked to the foraging pattern of parakeets. The extent of achene predation by parakeets was influenced by certain structural features of sunflower plants and not the resource load of each plant. Selective feeding on sunflower plants was governed by the predator vigilance pattern; parakeets prefer to feed on plants that offered better field of vision. The results suggest that the observed pattern of foraging by bird pests in agro-ecosystems is non-random and is dependent on factors favouring predator avoidance behaviour and not on resource maximization.
pp 381-389 October 1994
The white grub (Holotrichia sp: Scarabidae) is an important subterranean pest damaging root systems of several crops. Experiments conducted during I985 and I986 showed that at least I4 species of birds picked up the grubs exposed during ploughing operation. The important bird predators were mynasAcridotheres tristis (Linnaeus) andAcridotheres ginginianus (Latham), crowsCorvus splendens (Vieillot),Corvus macrorhynchos (Sykes), drongoDicrurus adsimilis (Hodgson) and cattle egretBubulcus ibis. The birds were found to reduce 45 to 65% grub population during 3 subsequent ploughings. The plant stand of second crop raised in bird exposed field was higher in experimental plot compared to the control. The number of birds attracted to the plough was not consistent with the density of grubs exposed but oh many extraneous factors. Factors affecting the extent of bird predation were presence of insectivorous birds in the surroundings, proximity to their breeding sites and timing of ploughing. White grub control by birds is economically cheaper and environmentally safe compared to the chemical control.
pp 391-402 October 1994
Agricultural ornithology aims at obtaining scientific information on birds in relation to agriculture and using this information for their management. Most of bird species play a useful role in agriculture by having a potent check on insect and rodent pests. However, some granivorous bird species, having adapted to the agricultural habitats and increased in numbers, are conflicting with our goals of agricultural production by inflicting economic losses to crops, fruits and stored grains. Bird management involves both the conservation of useful species and control of pests. Agricultural ornithology is of special importance in predominantly agricultural countries like India. Although a good deal of work has been done in this discipline in India, a lot remains to be done and, in fact, the discipline is still in its infancy. This paper reviews the progress made in agricultural ornithology in India, points out important problems and gaps in knowledge, and suggests approaches for future research.
pp 403-413 October 1994
An analysis of the concepts of ecomorphology is presented within a framework of areas of research in morphology, namely descriptive, functional, ecological and evolutionary morphology. A clear distinction must be made between functional and ecological morphology. The former is based on the concept of function and the latter on the concept of biological role. Although ecomorphology lies within the general area of evolutionary biology, explanations in ecomorphology are nomological-deductive and are distinctly different from explanations in evolutionary morphology which are historical-narrative.
pp 415-427 October 1994
With gradual increasing complexity in higher vertebrate structure and function, the birds as a class have acquired very high degree of feeding adaptations for diverse food-niches. A comparative functional morphological study of the feeding apparatus of 6 species of columbid birds showing diversification in their food-habits reveals that some correlations exist between the form-function complexes of the feeding apparatus and the extent of diversity of food-habits shown by these birds.
Among the species of columbid birds selected for the Study,Columba andStreptopelia are ground feeders and predominantly grain-eaters, although quite often they invade diversified food-niches.Treron andDucula, on the other hand, are almost exclusively fruit-eaters, plucking and swallowing fruits from the lofty tree branches, WhileColumba andStreptopelia show better kinesis of their jaws for ground-pecking,Treron. andDucula possess wider gape as well as stronger grasp of their bill for plucking off, grasping and swallowing large-sized fruits. Consequently, the size and pinnateness of the jaw muscles in these fruit-pigeons have developed far greater than those observed inColumba andStreptopelia. Further, inTreron andDucula, the thick and broad ‘venter externus’ slip of the M. pterygoideus ensures complete closure of the bill and possibly prevent any excess lateral expansion of the mandibular rami.
Similar correlations have also been observed between the tongue features of columbid birds and the diversity of their feeding adaptation.
pp 429-440 October 1994
A few avian species breed at altitudes up to 6500 m. Embryos in eggs laid at high altitudes are confronted with the problem that gases diffuse more rapidly at low barometric pressure than at sea level. Data on birds breeding up to 4500 m indicate that modifications in eggshell structure and embryonic physiology foster successful development in these groups. At moderate altitudes (up to 3600 m), shell conductance to gases (corrected to 760 torr) is decreased in approximate proportion to the reduction in barometric pressure, thus offsetting the increased tendency of gases to diffuse. At altitudes above 4000 m, the conductance is increased above levels at moderate altitudes, thus fostering improvement in oxygen availability, while increasing rates of water and CO2 losses. Above 4000 m, embryonic physiological properties become increasingly important for coping with hypoxic, hypocapnic, and dehydrated conditions inside the shell. Nothing is known about characteristics of eggshells and embryos in eggs laid between 4500 and 6500 m. Despite years of artificial selection, domestic fowl do not breed successfully much above 3000 m. Embryos of domestic fowl appear highly sensitive to the effects of hypoxia.
pp 441-451 October 1994
In the world-wide literature the role of predators and food shortage are considered as responsible for mortality of eggs and nestlings. In synantropic altricial hole-nestling birds such as sparrowsPasser domesticus (L.) andPasser montanus (L.) the predation plays unimportant role and in spite of this, mortality of eggs and nestlings can exceeded 50%. The role of microorganisms, heavy metals, pesticides and food shortage were investigated as possible causes of embryo and nestling deaths. About 70% of eggs that not hatched were infested with such pathogens asEscherichia coil, Staphylococcus epidermitis and several, more rarely occurring others. Considerable percentage of nestlings died due to pathogenic impact of such factors asEscherichia coli, Isospora lacazei, Candida spp., heavy metals and pesticides. As one effect of such interaction, the level of sublethal doses of heavy metals and pesticides are much lower that reported in the literature.
pp 453-466 October 1994
This paper reviews the factors and mechanisms which result in the development of the metabolic state characteristic of migration with special reference to a palaeotropic migrant the redheaded bunting,Emberiza bruniceps. Changes in climatic conditions and food supply act as proximate triggers of migratory behaviour in partial migrants. Typical migrants like buntings use daylength as a cue but the exact mechanism of how photoperiodic information is translated in terms of migratory events is still not known. Almost entirely the photoperiodic effects have been explained on the basis of the involvement of hypothalamo/hypophyseal system. We feel mechanism(s) other than those acting through neuroendocrine system may be equally important. Furthermore the role of temperature has not been adequately explored so far. Our observations indicate the possibility that redheaded buntings might integrate the information received from photoperiod with environmental temperature (and other factors?) resulting in the development of migratory state. The physiological control of avian migration is much less understood. Majority of papers have centered around the ‘gonadal hypothesis’ of Rowan supporting or contradicting it without providing conclusive evidence. Pituitary prolactin has also been shown to be implicated although the mechanism of action is only speculative.
Conclusive evidence for the involvement of thyroid hormones (thyroxine, T4; triiodothyronine, T3) in the physiological timing of migration has been produced attributing independent roles to T4 and T3. It is suggested that seasonal variation in peripheral conversion of T4 to T3 could serve as an effective strategy to render available the required thyroid hormones T4 and/or T3 during different phases of the year thus accounting for the metabolic switch over from T4-dependent moult to T3-dependent migratory fat deposition and zugunruhe and also ensuring preclusion of simultaneous occurrence of these mutually incompatible events. Considering that the number of environmental and physiological factors influence this mechanism and considering that thyroid hormone molecule has been put to a wide range of usage during the course of evolution the mechanism(s) of peripheral conversion of T4-T3 may assume great flexibility and have selective value-especially in migration which is known to have evolved several times in diverse avian families.
The attractiveness of this hypothesis lies in the fact that it has potential to explain the both physiological development of the metabolic state of migration and at the same time the physiological timing of migration not only with respect to the cycle of environment but also with respect to other conflicting seasonal events (moult and reproduction).
pp 467-477 October 1994
In the male black-headed bunting,Emberiza melanocephala, photostimulated testicular and/or body weight growth was followed by the regression. Transfer of photorefractory birds from 20L/4D to 23L/1D or from natural lighting (12–13 h) to 20L/4D failed to evoke testicular and/or body weight recrudescence. Thyroidectomy suppressed light-induced increase in the testes and resulted in early regression. Fully developed testes of breeding birds also regressed following thyroidectomy; an effect which was reversed by daily injections of 1 μg/bird of L-T4. Treatment with L-T4 at doses from 0·5-2·0 μ/bird/day/ 30 days had no effect on the testes of birds maintained on 12L/12D or following a shift from 12L/12D to 20L/4D. Photoinduced increase in body weight was inhibited by thyroidectomy; an effect which was reversed by treatment with L-T4 at dose level 1 μg/bird/day. The extent to which thyroidectomy decreased body weight of birds depended upon the lipid reserves at the time of operation. It is suggested that in the male black-headed bunting (i) breeding is terminated by development of absolute-gonadal and metabolic-photorefractoriness and (ii) thyroid hormones are necessary for sustaining light-induced increase in the gonads and/or body weight and for their maintenance, but not for the development of photorefractory state.
pp 479-484 October 1994
We administered a blindness-inducing substance (formoguanamine hydrochloride) to Japanese quail in order to find whether it is effective to induce retinal degeneration in avian species other than the chicken. We also investigated its effects on the photoperiodic response of various organs including gonads and the entrainment of circadian locomotor activity rhythms. Histological observation revealed conspicuous degeneration of the photo-receptor outer segments and pigment epithelium. Behavioural responses of formoguanamine hydrochloride-treated birds to visual stimuli were completely abolished. These results proved that this chemical substance is effective to induce blindness in avian species other than the chicken. In formoguanamine hydrochloride-treated birds, the locomotor activity rhythm was entrained to light-dark cycles and the photoperiodic gonadal response was almost normal, suggesting that the extraretinal photoreceptors remained intact even after the formoguanamine hydrochloride-treatment.
pp 485-489 October 1994
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.
pp 491-502 October 1994
Once the Japanese ibis, or the Japanese crested ibis, was widely distributed in Asia including Japan, Korea, China and Siberia, and was not a rare species. However, this species started to disappear over its entire range beginning in the late 19th or early 20th century. Currently, only a single population of 15–20 individuals survives in wild in Yang Xian, Shaanxi, China. Several individuals, mostly immature birds, are kept in captivity in Beijing zoo. One of them is an adult male captured in 1981 in Japan and sent to Beijing zoo for breeding two years ago. In Japan, only, a single old female survives in captivity. Scientists of the Japanese Ibis Preservation Center in Sado Island and Ueno zoo, Tokyo, had attempted several times to breed Japanese ibises in captivity, but they have failed in all of their attempts. In Beijing zoo, a similar attempt is now being carried out.
As the basis of an artificial breeding programme of this and other species of birds, the authors have attempted to establish a noninvasive method for estimation of gonadal activities of birds and also a method to induce a complete series of the ovarian activity,i.e., ovarian growth, ovulation and oviposition, by means of hormone administration to some species of birds. In this communication, the author briefly reports recent results of these attempts in addition to results of measurements of gonadotropin levels in plasma of captive Japanese ibises and white ibises, a closely related species,Threskiornis aethiopicus.
pp 503-509 October 1994
Landscape ecology as a discipline in science is rather young. However its principles appear promising in outlining conservation strategies including a wide range of organisms, particularly birds. Birds due to their mobility use a variety of environmental resources, especially habitats. However, currently these habitats are only available in patches over most of the tropical world. Further whatever is left is under constant human pressure. This paper, therefore, addresses this problem and suggests means of dealing with it using the landscape approach as outlined by landscape ecology.
The landscape approach starts with the realization that patches of habitats are open and interact with one another. Corridors of trees along roads, hedgerows and canals in a landscape can aid in the movement of species. Hence the landscape approach considers patches of habitats as interacting elements in the large matrix of the landscape. The landscape approach also integrates concepts. It puts together often debated issues such as whether to preserve maximum species diversity, to maximize representativeness, or to preserve only the valuable species. Based on a case study of the Uttara Kannada district in Karnataka, these oft-opposing views and complications can be dealt with practically and synthesized into a conservation strategy for the diverse avifauna of the Western Ghats.
Volume 44 | Issue 5
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