Breeding Success in Some African Eagles Related to Theories About Sibling Aggression and Its Effects

Brown, Leslie H.; Gargett, Valerie; Steyn, Peter

doi:10.1080/00306525.1977.9634083

Cited by 43 publications

(25 citation statements)

References 12 publications

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“…Other species with persistent, unconditional sibling aggression occasionally have surviving broods of two (Brown et al 1977;Evans 1996;Tershy et al 2000), but broods of two Nazca booby chicks were quickly reduced to a single chick in virtually all of the families that we studied. In only one family did two siblings survive to the 1% down developmental stage, and in this case, one of the chicks was in such poor condition that it almost certainly did not survive to independence.…”

Section: Discussionmentioning

confidence: 97%

Contributions of marginal offspring to reproductive success of Nazca booby (Sula granti) parents: tests of multiple hypotheses

et al. 2005

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While obligate siblicide is a phylogenetically widespread behavior, known from plants, insects, birds, and other taxa, with important implications for life history evolution, comprehensive evaluations of its costs and benefits to parents are rare. We used 12 years of breeding and band resight data to evaluate the importance of several potential benefits that marginal offspring (the usual victims of obligate siblicide) could provide to parent Nazca boobies (Sula granti), a seabird. We found no evidence for the resource-tracking hypothesis: 99.95% of two-chick broods were reduced to one chick before fledging, and the single exceptional brood probably lost one chick between fledging and independence. Behavioral observations indicated that siblicidal aggression caused most mortality of marginal chicks, and at least contributed to the remainder. We also found no evidence that marginal offspring provide a food resource for other family members. Marginal chicks benefit parents via adoption into other families, and possibly also in the context of progeny choice, but these benefits are minor compared to the insurance that marginal chicks provide against early failure of core (first-hatched) offspring. Further evaluation of the Insurance Egg Hypothesis showed that marginal and core offspring are functionally equivalent in the absence of sibling interactions, and that core offspring incur no detectable costs from behaving siblicidally. Nazca boobies are truly obligate brood reducers, with parents receiving principally insurance benefits from marginal offspring, but many birds and other taxa exhibiting persistent, unconditional sibling aggression do not exhibit universal brood reduction. Insurance is only one of several potential benefits that marginal offspring can confer on parents, and a multi-hypothesis approach to decompose the different types of benefits is required to understand the evolution of clutch size in other obligately siblicidal species.

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Section: Discussionmentioning

confidence: 97%

Contributions of marginal offspring to reproductive success of Nazca booby (Sula granti) parents: tests of multiple hypotheses

et al. 2005

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“…Overall, the Spanish imperial eagle, in comparison with other large birds of prey, including its congeneric, the Eastern imperial eagle (A. heliaca), (Svehlik and Meyburg 1979;Danko and Chavko 1996), has some of the highest population breeding parameters known (clutch size, fledging rate and hatching success) (see Brown and Amadon 1968;Newton 1979;Cramp and Simmons 1980;Brown et al 1977;del Hoyo et al 1994;Watson 1997).…”

Section: Breeding Biology and Population Parametersmentioning

confidence: 97%

“…Nest change can be useful in order to avoid the accumulation of parasites as a result of the build-up of prey items (Brown and Amadon 1968;Margalida and Bertran 2000), something that has been seen to cause chick mortality and desertion of the nest (Herman 1955;Feare 1976;Wimberger 1984). The reasons for Spanish imperial eagles to build and change nests can also be due to other factors, such as the substitution of one member of the pair, disturbance in the nesting sector (human disturbance in particular) or as an alternative when the first nesting attempt fails (Brown 1969;Newton 1979).…”

Section: Breeding Biology and Population Parametersmentioning

confidence: 99%

A long-term large-scale study of the breeding biology of the Spanish imperial eagle (Aquila adalberti)

Margalida¹,

González

Sánchez³

et al. 2007

J Ornithol

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We present data from a 17-year study of the population biology of a growing population of Spanish imperial eagles Aquila adalberti across most of its breeding range. The objective of this study was to analyse the effects of age, supplemental feeding and rabbit haemorrhagic disease (RHD) on several breeding parameters of this population of eagles. Average clutch size was 2.2 eggs per clutch, and the average incubation time was 41.7 days per clutch. Fledging occurred an average of 76.8 days after hatching, the length of the fledgling period was not correlated to clutch size. The annual average percentage of pairs laying eggs was 88%. A significant reduction in the percentage of pairs laying eggs in the period 1992-1994 (from 91 to 81%) coincided with most of the eagles' territories being affected by the rabbit epizootic disease, RHD, which reduced their food supply significantly.Average productivity was 1.23 chicks per monitored territory, average breeding success was 1.40 chicks in a clutch per territory and the average fledging rate was 1.69 chicks per territory with hatching success. The main known causes of breeding failure during incubation were nest collapse and human disturbance. During chick-rearing, total or partial chick losses were mainly caused by siblicide, disease, malnutrition or nest collapse. In 26.2% of the 1372 monitored breeding attempts, at least one of the breeding birds was a subadult (the male in 56.1% of the cases, the female in 15.5% and both sexes in 28.4% of cases). In cases of mixed-aged pairs (n = 205), 70.7% were the result of a substitution, and 29.3% were the result of the forming of a new pair. Egg laying took place significantly earlier and breeding success was higher in territories occupied by adults than in those occupied by subadults. Breeding parameters were higher in high-quality (rabbit-rich) territories than in low-quality (rabbit-poor) territories, but only for those territories occupied by adults. The values obtained in the territories occupied by adults were only significantly higher than in those of the subadults in highquality territories. Age and territory quality thus simultaneously affected reproductive output.

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“…Insects I Total of all prey items I 92 Table 1 summarizes all prey items found at Essexvale nests and incorporates those of the earlier study (Steyn 1962) except that five unidentified items have been excluded. In Table 2 prey at Essexvale is compared with that in Kenya (Brown 1952(Brown ,1955Smeenk 1974) and in the Transvaal, South Africa (Tarboton 1977). An account by Snelling (1969) (Brown 1952(Brown , 1955 Table 2 shows strikingly similar results at Embu and Essexvale, while in Tsavo birds constituted a very high part of the total, and in the Transvaal mammals and birds were most often recorded, although amphibians featured prominently too.…”

Section: S Eaglementioning

confidence: 99%

“…In a total of 26 pair-years at Essexvale 19 young were reared, a replacement rate of 0,73 young1 pair/year, one of the highest on record for an African eagle (Brown et al 1977, Osrrich 4855-71). One egg infertile.…”

Section: Further Observations On Tbe Tawny Eaglementioning

confidence: 99%

Short Notes

McGrew

Myburgh

Steyn³

1980

Ostrich

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Breeding Success in Some African Eagles Related to Theories About Sibling Aggression and Its Effects

Cited by 43 publications

References 12 publications

Contributions of marginal offspring to reproductive success of Nazca booby (Sula granti) parents: tests of multiple hypotheses

Contributions of marginal offspring to reproductive success of Nazca booby (Sula granti) parents: tests of multiple hypotheses

A long-term large-scale study of the breeding biology of the Spanish imperial eagle (Aquila adalberti)

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