Food requirements and the timing of breeding of a cape vulture colony
TL;DR: The period between 60 and 100 days after hatching was the most critical period of food demands, because this was the period of greatest nestling food requirements and daily family food intake was effectively constant due to temporal constraints on foraging.
Abstract: Summary Komen, J. & Brown, C.J. 1993. Food requirements and the timing of breeding of a Cape Vulture colony. Ostrich 64:86-92. Annual food requirements of a Cape Vulture Gyps coprotheres family, comprising one nestling and two adult birds, and a breeding colony were estimated. A family required 226,1 kg meat during a nestling period of 136 days, and 524,4 kg annually. The greatest family food requirements (average 1,98 kg/day) occurred between 60 and 100 days after hatching. The period between 60 and 100 days after hatching was the most critical period of food demands, because (a) this was the period of greatest nestling food requirements, (b) only one parent could be away from the nest at a time, and (c) daily family food intake was effectively constant due to temporal constraints on foraging. The estimated food requirements of a breeding colony comprising 152 breeding pairs and 98 nonbreeding birds was 89 388 kg meat annually, and 36 892 kg during the nestling period, with the highest food requirements ...
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TL;DR: In this article, the authors studied Griffon Vultures Gyps fulvus in order to describe the pattern of competition between ages and sexes, assess the effect of reintroduction on competitive behaviour, and study the potential consequences of food management on competition.
Abstract: Intraspecific competitive behaviours were studied in a reintroduced population of Griffon Vultures Gyps fulvus in order to describe the pattern of competition between ages and sexes, assess the effect of reintroduction on competitive behaviour, and study the potential consequences of food management on competition. There was no evidence for a difference in feeding or display rates between age classes. However interaction rates, aggressiveness and dominance were higher in old adults than in the other age classes. No difference in the pattern of competition was found between sexes. There was no difference in the competitive ability (feeding rate and dominance) of reintroduced and wild-bred individuals. Feeding rates increased with resource availability. Group size also increased with food mass, but was lower than the theoretical maximum number of birds. This may be evidence of competition by interference where some individuals are able to increase their feeding rate by the exclusion of others. An increase in both the number of carcasses and the number of feeding sites is thus recommended to induce dispersal and reduce this competition.
53 citations
TL;DR: The main behavioural patterns examined were aerial displays, nest defence, copulation, nest building, brooding and food provisioning to the chicks, which showed similarities among this insular population and continental ones.
Abstract: A field study of the breeding behaviour of griffon vultures (Gyps fulvus) was conducted in Crete (Greece) during 1997–2000. The main behavioural patterns examined were aerial displays, nest defence, copulation, nest building, brooding and food provisioning to the chicks. The nesting territory consisted of a semicircle ca 5 m radius around the nest that was defended against conspecifics. Copulation attempts mainly occurred in the nesting ledge with a success rate of 77%. On average every pair accomplished 0.16 ± 0.34 copulations per day (range = 0–4) while 3.3% of the total attempts accounted for extra–pair copulations. Supplying material to the nest started 32 ± 9 days prior to egg laying (range = 17–44) at a rate of 5 ± 3.52 bouts/pair/day (range = 1–14).The mean number of items added to the eyrie was 2 ± 1.3/bout/pair (range = 1–8) with 63.5% of these being soft greenery.The mean frequency of relief at the nest relieves was 0.5 ± 0.64 bouts/pair/day (range = 0–2) while an incubation shift lasted on aver...
41 citations
Journal Article•
TL;DR: The timing of bird breeding in Namibia and the sizes of clutches and nesting colonies are presented per species, derived from 7 231 nest record cards, over 300 publications, museum and private egg collections and via personal communications.
Abstract: The timing of bird breeding in Namibia and the sizes of clutches and nesting colonies are presented per species, derived from 7 231 nest record cards, over 300 publications, museum and private egg collections and via personal communications.
21 citations
Cites background from "Food requirements and the timing of..."
...The mid-nestling period in some vulture species is critical as only one adult at a time can forage to provision a nestling that requires at least as much food as an adult; this period coincides with the time of highest wildlife mortality (Brown 1988, Komen & Brown 1993)....
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TL;DR: Investigating the effect of supplementary food on population dynamics and breeding success in a breeding colony of the Cape Vulture Gyps coprotheres and a nearby vulture restaurant in South Africa indicates that carefully managed vulture restaurants might stabilise vulture colonies and can therefore aid vulture conservation.
Abstract: The number of vultures is declining in many parts of the world due to numerous threats, such as poisoning and collisions with power-lines as well as the lack of adequate food sources. Vulture restaurants, i.e. supplementary feeding stations, have become a widespread conservation tool aimed at supporting vulture colonies. However, it is poorly understood how vulture restaurants influence population dynamics and whether they affect breeding success of vulture populations. We used a 12-year dataset from a breeding colony of the Cape Vulture Gyps coprotheres and a nearby vulture restaurant in South Africa to investigate the effect of supplementary food on population dynamics and breeding success. We found a significantly positive effect of supplementary food during the nest-building stage on the number of breeding pairs. However, breeding success, i.e. the proportion of successful nests, did not depend on supplementary food during the incubation and rearing stage. Especially during the critical rearing stage, the amount of food supplied might not have been sufficient to meet food demands of the colony. Still, our results indicate that carefully managed vulture restaurants might stabilise vulture colonies and can therefore aid vulture conservation.
13 citations
Cites background from "Food requirements and the timing of..."
...Overall, a family (i.e. two adult birds and one nestling) is estimated to require 230 kg of meat during the entire nestling period (Komen and Brown 1993)....
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TL;DR: In this article , the authors assess home range size and their overlap with protected areas by species, age, breeding status, season, and region using a large continent-wide telemetry datasets that includes 163 individuals of three species of threatened Gyps vulture.
Abstract: Protected areas are intended as tools in reducing threats to wildlife and preserving habitat for their long-term population persistence. Studies on ranging behavior provide insight into the utility of protected areas. Vultures are one of the fastest declining groups of birds globally and are popular subjects for telemetry studies, but continent-wide studies are lacking. To address how vultures use space and identify the areas and location of possible vulture safe zones, we assess home range size and their overlap with protected areas by species, age, breeding status, season, and region using a large continent-wide telemetry datasets that includes 163 individuals of three species of threatened Gyps vulture. Immature vultures of all three species had larger home ranges and used a greater area outside of protected areas than breeding and non-breeding adults. Cape vultures had the smallest home range sizes and the lowest level of overlap with protected areas. Rüppell's vultures had larger home range sizes in the wet season, when poisoning may increase due to human-carnivore conflict. Overall, our study suggests challenges for the creation of Vulture Safe Zones to protect African vultures. At a minimum, areas of 24,000 km 2 would be needed to protect the entire range of an adult African White-backed vulture and areas of more than 75,000 km 2 for wider-ranging Rüppell's vultures. Vulture Safe Zones in Africa would generally need to be larger than existing protected areas, which would require widespread conservation activities outside of protected areas to be successful.
5 citations
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TL;DR: In this paper, the parent adjusts its effort in relation to prevailing environmental conditions in order to maximize the output of young in its lifetime, rather than measurable in terms of adult survival and recruitment of young.
Abstract: 1. Energetics of reproduction in birds is reviewed with the question in mind how the parent adjusts its effort in relation to prevailing environmental conditions in order to maximize the output of young in its lifetime. Emphasis is on proximate controls, rather than ultimate factors measurable in terms of adult survival and recruitment of young. 2. The decision to breed or not to breed is clearly related to body condition of the female, presumably because of the implications this has for survival. 3. Laying date and clutch size are likewise under the influence of female condition and can hence be modified by experiments involving supplementary feeding. Natural variation in these features may often be related to territory quality. 4. How the bird decides whether or not to commence a second brood is not clear, but in the Great Tit the habitat-related difference in incidence of second broods is functionally understandable when survival probabilities of birds at different times are considered. 5. A distinction is made between a "capital" and "income" model for translatting rates of change of female body condition into appropriate decisions on laying date and clutch size and experiments are suggested that discriminate between the two. 6. Lack's view that brood size is in an evolutionary sense adjusted in order to balance food requirement and foraging capacity of the parents is accepted, and growth rates in nidicolous birds are analysed to ascertain if a finer adjustment exists superimposed on the integer steps of brood adjustment. Critical for this analysis are groups of birds where broods of one are common, since only in these circumstances is growth adjustment the only strategy open to the parents. In common with other animals, growth rate is related to mature body size but within a category of adult weight clear examples can be found for retardation of growth rate in pelecaniform and charadriiform species with singleton broods. 7. Since daily energy requirement is related to nestling size and growth rate, retardation of growth is explicable as a strategy only in terms of reducing the daily commitment of the parents, not reducing the total cost of producing a nestling. 8. An additional economy in growth is to reduce the contribution of fat to the nestling body. 9. Implied in Lack's view of brood size is a limitation of parental foraging capacity, and the last section of the paper is devoted to exploration of the proximate factors delimiting what Royama terms the optimal working capacity of parents feeding young. Observations of parent starlings confronted with manipulated brood size suggest a limit on the time that can be devoted to energetically extravagant flight activity, rather than a shortage of absolute time. Beyond the limit to which stressed parents can be made to fly, body weight declines. 10. Preliminary data on energy metabolized daily by parents confronted with large broods conforms to the simplified view that parental effort on a sustained basis equates to energy mobilization equivalent to 4 B.M.R. units and it is suggested that this level of energy expenditure represents a proximal decision substrate for determining the optimal working capacity of the parent. 11. The paper ends with a plea for more research on the proximate controls of avian reproduction, and calls attention to the central importance of the protein bank to parental body condition.
2,070 citations
TL;DR: The results of a field study on food consumption of free-living nestling I)ouble-crested Cormorants, Phalacrocorax auritus are given.
Abstract: ENERGY requirements of altricial nestlings should have effects on optimal reproductive strategy and foraging efficiency of adults, and on developmental physiology of nestlings (Royama 1966, I)unn 1973). Most food consumption studies measure weight of food intake without considering nutritional value. Because avian foods vary widely in digestibility, nutrition, and caloric content, such measures of food consumption of different species are not always comparable. In addition, many studies examine only total quantities of food eaten during growth (e.g. Kale 1965, Brenner 1968) or deal with birds raised in captivity (e.g. Kahl 1962, Junor 1965). The latter may not indicate natural levels of food consumption, as it is difficult to duplicate normal foods and feeding rates. For example Junor's (1965, 1972) studies indicate that the amount of food captive young Reed Cormorants, Phalacrocorax africanus, consume differs markedly according to the number of times per day they are fed. I am aware of only a few studies to date that have estimated daily consumption of altricial nestlings under natural conditions (Royama 1966, Koelink 1972, van Balen 1973, Westerterp 1973), and only the latter provided data on the caloric value of the foods eaten. This paper gives the results of a field study on food consumption of free-living nestling I)ouble-crested Cormorants, Phalacrocorax auritus. (Unless noted otherwise, all references to cormorants mean this species.) Feeding frequency and size of food items were used to indicate quantities eaten, and analysis of food samples and digestive efficiency allowed conversion to caloric intake. The report is mainly descriptive, and the correlation of results to other aspects of the breeding strategy of cormorants will be reserved for a later paper.
113 citations
TL;DR: The comparison of the estimates of the food obtained and the food required through the breeding season suggested that there may be a period during rearing when there was insufficient food available to satisfy the food requirements of both chick and adult.
Abstract: Summary
The breeding season of two species of griffon vultures are described. Ruppell's Griffon Vulture lays 2–3 months earlier than the White-backed Griffon. Young birds were hand-reared to determine their food requirements during growth; these estimates were combined with the food requirements of adult birds to make an estimate of the amount of food a parent bird needs to obtain when it is rearing young. The amount of food actually obtained by a group of birds was recorded from the size of the crops of birds returning to the breeding colony in the afternoon. The comparison of the estimates of the food obtained and the food required through the breeding season suggested that there may be a period during rearing when there was insufficient food available to satisfy the food requirements of both chick and adult. Chicks were found to have a very high survival rate and were probably receiving sufficient food. Presumably adult birds were not therefore receiving sufficient food, and the examination of a sample of adult birds for body condition through the breeding season showed a clear decline in their fat deposits. It was considered that in both species, breeding was timed so that the young left the nest at a period in the year when food conditions were good and the young birds could feed with little competition from adults. The parent birds therefore had to rear young during a season in the year when food conditions were not always adequate and they had to rely on utilising fat reserves. The food conditions for vultures during this study were probably favourable and during years of food shortage breeding may become impossible, or restricted to the most aggressive and dominant individuals.
84 citations
01 Jan 1969
TL;DR: In this paper, Populations in a Transvaal Lowveld Nature Reserve were studied and the authors proposed a method to estimate the number of animals living in the reserve, and the extent to which they inhabited the reserve.
Abstract: (1969). Populations in a Transvaal Lowveld Nature Reserve. Zoologica Africana: Vol. 4, No. 2, pp. 199-230.
67 citations