Nest-guarding Behavior Research Articles

Intraspecific nest parasitism and anti-parasite behavior in the grey starling,Sturnus cineraceus

I studied intraspecific nest parasitism in the grey starlingSturnus cineraceus in 1992 and 1993. The population in this study consisted of 290 nests (157 nests in 1992 and 133 nests in 1993) in which the clutches were completed before May 10 in the year studied. Twenty-nine nests in 1992 and 32 nests in 1993 contained at least 1 parasitic egg. Hatching success per nest of parasitized nests was slightly higher than that of non-parasitized nests. However, fledging success per nest of parasitized nests was significantly lower than that of non-parasitized nests. Thus parasitism appeared to reduce the reproductive success of hosts. Hosts exhibited a few behaviors that minimized the potential cost of brood parasitism. These behaviors included throwing out the parasitic egg and nest guarding. Hosts threw out parasitic eggs before the onset of laying, but they never did so to parasitic eggs laid after that period. The nest guarding level was low during the hosts’ laying periods, and one observed nest was parasitized during this time. Thus, nest-guarding behavior was not effective as an anti-parasite behavior. Grey starlings do not appear to adopt strategies effective in reducing parasitism.

The effect of male removal on female parental care in the orange-tufted sunbird

The importance of male care and the nature of facultative adjustments in female care were assessed by experimentally removing males in pairs of orange-tufted sunbirds,Nectarinia osea, feeding broods of two or three chicks. The predation of all three-chick broods with female-only care suggested that male nest guarding is critical, especially because males also deter infanticidal floater males. Comparison of provisioning and nest guarding behaviour in male-removed and control nests was therefore limited to two-chick broods. As expected, lone females provisioned at a greater rate, but compensated incompletely for the lack of male provisioning effort. Surprisingly, even when provisioning at high rates, lone females still performed the usual levels of nest guarding and nest sanitation. Lower rates of chick mass gain in the nest, and subsequent premature disappearance of fledglings from male-removed broods, confirmed that reduced provisioning to broods of lone females had detrimental effects upon chick fitness. Sunbirds exhibit sex-specific roles in parental care. Female provisioning appears flexible, ensuring adequate care for young in the nest. Nest guarding is incompatible with high foraging effort, but it may be compatible with male non-parental activities such as territorial defence and extra-pair mating. These results concur with recent data concerning male responses to experimentally reduced female care in this species, and are discussed in terms of evolutionary strategies for stable biparental cooperation.

Benefits and Costs to Plain-Fronted Thornbirds (Phacellodomus rufifrons) of Interactions with Avian Nest Associates

AnSTRACT.--From 1990 through 1993, I examined the interactions among a group of bird species in central Venezuela that use the multichambered stick nests of the Plain-fronted Thornbird (Phacellodomus rufifrons). Eleven species besides thornbirds, referred to as associates, used thornbird nests as nest sites and, in some cases, roost sites. During the 18-month study, 130 incidents of associates nesting in thornbird nests were recorded. More than 90% of thornbird territories observed for at least two breeding seasons (n = 33) had at least one associate nesting attempt. Four species accounted for over 86% of the attempts by associates: Cattle Tyrants (Machetornis rixosus), Stripe-backed Wrens (Campylorhynchus nuchalis), Saffron Finches (Sicalis fiaveola), and Troupials (Icterus icterus). Sometimes thornbird and associate nesting attempts overlapped, taking place within the same nest in different chambers, or in different thornbird nests within a territory. Nine of 27 (33%) thornbird nesting attempts at the beginning of the 1991 breeding season overlapped associate attempts, and 5 of 26 (19%) overlapped in 1992. Nesting with associates involved benefits and costs for the thornbirds. In 1991, thornbird nesting attempts that overlapped Troupial nesting attempts were no more likely to succeed (33% successful, n = 6) than attempts with no associate overlap (28% successful, n = 18). Thornbird attempts that overlapped those of other species, however, were significantly more likely to succeed than attempts with no overlap (100% successful, n = 3). In 1992, patterns were similar (0% successful with Troupials, n = 2; 10% successful with no associates, n = 21; 33% successful with other associates, n = 3), although high thornbird nest mortality and small sample sizes precluded statistical analysis. Thornbird nesting attempts that overlapped two associate nesting attempts (n = 7, 1991 and 1992 combined) had a high success rate (71%). Rainfall in the month before fledging was positively associated with the number of fledglings produced in 1991, but not in 1992. Nest-guarding behavior by associates and enhanced mobbing of predators (demonstrated in predator-presentation experiments) were likely mechanisms of enhanced reproductive success when thornbirds nested with associates. Thornbirds often were treated with aggression by associates, and circumstantial evidence indicated that Troupials sometimes preyed on thornbird eggs and nestlings. Valuable nest sites may lead coexisting species to converge, rather than diverge, in their use of this resource. Received 20 February 1995, accepted 26 July 1995.

Nesting Ecology of the Little Blue Heron: Promiscuous Behavior

Sixty-four extramarital copulations were observed from 19761978 in a nesting colony of Little Blue Herons (Florida caerulea). In almost all cases the male and female involved had paired and the female had not completed egg-laying. Extramarital copulations occurred at the female's nest site; the intruding male nested nearby. All but one of the extramarital copulations occurred when the paired male was away from the nest site. The paired male, when present, and the female supplanted intruding males. However, once mounted, the female's extramarital copulatory behavior was passive, similar to that with her mate. This apparent lack of resistance may not have been cooperative but rather a way to reduce reproductive failure due to the egg loss that sometimes occurred during extramarital copulations. Overall, extramarital copulations occurred relatively infrequently, owing to: (1) the nest-guarding behavior of the pair male, and (2) the uncooperative behavior of the female. The selective pressures favoring colonial nesting must be strong because such behavior has disadvantages (Hoogland and Sherman 1976). One such drawback for males is the competition for females caused by the accessibility of females to other males besides their mates during the copulatory period. A male must not only attract a mate but also avoid wasting time and effort raising offspring not his own (Trivers 1972, Beecher and Beecher 1979). Furthermore, when extramarital or promiscuous copulations are frequent it may not be advantageous for males to participate in the rearing of young. For this reason, when care by both parents is necessary for nestling survival, selection is thought to favor those females who are monogamous (rather than promiscuous) and resist extramarital copulations (Gladstone 1979). Thus, colonial nesting contains conflicting selective pressures. Male promiscuity, which should be favored, will weaken selective pressures for males to participate in brood rearing. The resolution of this conflict will, in part, determine the structure of the mating sys-

Spatial and temporal multi-species nesting aggregations in birds as anti-parasite and anti-predator defenses

1. The purpose of this study was to determine whether the yellow warbler (Dendroica petechia) derives any benefits from nesting in close proximity to its own and other species in reducing predator pressure or the incidence of brood parasitism by the brown-headed cowbird (Molothrus ater). 2. Yellow warblers nesting synchronously with their own and with neighbouring species resulted in a proportionate reduction in the number of nests preyed upon, suggesting a ‘swamping effect’ of the local predators. A significantly lower incidence of predation occurred at yellow warbler nests which were inside a gray catbird (Dumetella carolinensis) response range. This was thought to be the result of yellow warblers taking advantage of the catbird's nest-guarding behaviour and aggressive responses to predators. 3. Yellow warblers nesting synchronously with other yellow warblers were subject to a proportionately lower incidence of brood parasitism than asynchronous nests, suggesting a ‘swamping effect’ on the cowbird. A significantly lower incidence of brood parasitism occurred at yellow warbler nests which were in a red-winged blackbird (Agelaius phoeniceus) response range. The yellow warbler was thought to be taking advantage of the aggressive response of red-winged blackbirds to cowbirds. 4. Overall, yellow warblers which nested within the response range of red-winged blackbirds or gray catbirds had significantly higher nest success than other yellow warblers. This suggests that selection for defence against predators and cowbirds may lead to multi-species aggregations.