The Experts below are selected from a list of 4524 Experts worldwide ranked by ideXlab platform
Spencer G Sealy - One of the best experts on this subject based on the ideXlab platform.
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Acceptance of Simulated Cowbird Parasitism in a Northern Population of Red-Winged Blackbirds
The American Midland Naturalist, 2012Co-Authors: Christie-leigh Capper, Mélanie F. Guigueno, Spencer G SealyAbstract:Abstract Red-winged Blackbirds (Agelaius phoeniceus) may be more likely to desert nests parasitized by Brown-headed Cowbirds (Molothrus ater) when they interact with the parasite, because desertion frequencies are higher at naturally parasitized nests than at artificially parasitized nests in some brood-parasitic hosts. We experimentally parasitized blackbird nests in southern Manitoba with Cowbird model eggs and presented taxidermic mounts of adult female Cowbirds near their nests. We observed no desertion, which is possibly attributable to constraints of a shorter breeding season at this latitude. We also compared rejection frequencies for blackbirds when a mounted female Cowbird was placed near the nest to rejection frequencies recorded when (1) no model egg was added, (2) a model egg was added but no mounted Cowbird was presented, and (3) a model egg was added plus presentation of a mount of a non-parasitic and non-threatening species, the Fox Sparrow (Passerella iliaca). Blackbirds struck the Cowbird...
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nest defence against avian brood parasites is promoted by egg removal events in a Cowbird host system
Animal Behaviour, 2011Co-Authors: Daniela Campobello, Spencer G SealyAbstract:Recent studies of birds have found that the antiparasite behaviour of host species is modified by social learning. We tested whether individual or social learning modifies the nest defence of yellow warblers, Setophaga petechia, against the parasitic brown-headed Cowbird, Molothrus ater. Using field experiments, we exposed warblers to simulated events of nest parasitism and predation, or allowed them to observe conspecifics mobbing a Cowbird. Intensity of nest defence by yellow warblers was greater after simulated threats at their nest than after they had observed mobbing of Cowbirds by conspecifics. Warblers defended their nests more aggressively when they perceived a Cowbird as an egg predator rather than as a parasite. Higher predation than parasitism frequencies probably explain the more prompt change in defence when Cowbirds were encountered as egg predators. Annual fluctuations in frequencies of both parasitism and predation suggest that defence acquired via observing conspecifics may contain outdated information and probably explains the warblers’ reliance on individually learned over socially learned defence.
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Changes in Nest Defense against a Brood Parasite over the Breeding Cycle
Ethology, 2010Co-Authors: James V. Briskie, Spencer G SealyAbstract:We measured the responses of nesting least flycatchers (Empidonax minimus) to a model of the brood-parasitic brown-headed Cowbird (Molothrus ater). A greater number of vocalizations, approaches and threat displays were directed toward the Cowbird model than toward a control model of a fox sparrow (Passerella iliaca), suggesting that the Cowbird was recognized as a threat. Flycatchers were more likely to give threat displays during laying when the consequences of brood parasitism were greatest; however, the intensity of all other defensive behavior did not change over the nesting cycle. We suggest that least flycatchers remained aggressive throughout nesting because Cowbirds were also predators on eggs and nestlings.
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does nest defence deter or facilitate Cowbird parasitism a test of the nesting cue hypothesis
Ethology, 2010Co-Authors: Sharon A Gill, Paula M Grieef, Lisa M Staib, Spencer G SealyAbstract:The nesting-cue hypothesis poses that avian brood parasites use nest-defence responses directed toward them by hosts as cues to locate nests to parasitize. Hosts that respond more intensely to brood parasites should provide more cues about nest location than those hosts giving lower intensity responses. Thus, the nesting-cue hypothesis predicts that within a species parasitized nest owners should respond more intensely than unparasitized nest owners to Cowbirds perched near and away from nests. This assumes that hosts respond to Cowbirds when they are encountered away from the nest and that host responses gradually increase in intensity as the Cowbird nears the nest. The nesting-cue hypothesis, its assumptions and prediction were tested using six host species of the brown-headed Cowbird (Molothrus ater, Icterinae). We presented a female Cowbird model at three distances from host nests and compared the responses elicited. All species responded to the Cowbird at all distances, which supports the first assumption. Some of the rarely elicited responses (e.g. contacts) and the proximity of the host to the model varied significantly with distance, which suggests that Cowbirds could use nest defence by the host as cues to the location of an active nest. However, parasitized nest owners did not respond more intensely than unparasitized nest owners to the Cowbird positioned at any of the distances from the nest, which does not support the nesting-cue hypothesis itself. Further considerations are discussed that suggest that nest defence is not likely to be used as a nest-location cue.
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Experiments on the responses of a rejector species to threats of predation and Cowbird parasitism
Ethology, 2010Co-Authors: Ronald C. Bazin, Spencer G SealyAbstract:We presented freeze-dried models of a nondescript sparrow (control), a female brown-headed Cowbird (Molothrus ater, Icterinae) and an avian nest predator to nesting eastern kingbirds (Tyrannus tyrannus, Tyranninae) during the egg-laying and nestling stages to test for nest defense against the threat of Cowbird parasitism. Both kingbird parents responded during 81% of the 183 trials. Kingbirds responded aggressively toward the Cowbird model, but only slightly more so than to the control, and less than to the predator model. The level of aggression directed toward the predator increased between the laying and nestling stages. The results suggest that kingbirds at Delta Marsh, Manitoba, did not recognize the Cowbird as a unique or dangerous threat, possibly because of low selection pressure on this rejector species for aggressive nest defense against Cowbirds.
Juan C Reboreda - One of the best experts on this subject based on the ideXlab platform.
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reproductive success of the specialist brood parasite screaming Cowbird in an alternative host the chopi blackbird
The Auk, 2015Co-Authors: Alejandro G Di Giacomo, Juan C ReboredaAbstract:ABSTRACT The Screaming Cowbird (Molothrus rufoaxillaris) is the most specialized brood-parasitic Cowbird, relying almost entirely on the Bay-winged Cowbird (Agelaioides badius) as host. Recently, Screaming Cowbirds have expanded their range to areas where Bay-winged Cowbirds are absent, and they are exploiting the Chopi Blackbird (Gnorimopsar chopi). Interactions between Screaming Cowbirds and Chopi Blackbirds are largely unexplored, as is the reproductive success of the parasite in this host. Screaming Cowbirds, Chopi Blackbirds, and Bay-winged Cowbirds coexist in northeastern Argentina, providing an ideal system to explore interactions between a specialist brood parasite and an alternative host and to compare the reproductive success of the parasite in its main host and in an alternative host. Screaming Cowbirds parasitized both hosts throughout their breeding seasons (Chopi Blackbirds, mid-October to mid-January; Bay-winged Cowbirds, mid-November to mid-March). Frequency of parasitism was lower in Chop...
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Strategic egg destruction by brood-parasitic Cowbirds?
Animal Behaviour, 2014Co-Authors: Vanina D. Fiorini, Ros Gloag, Alex Kacelnik, Juan C ReboredaAbstract:Obligate avian brood parasites do not provide direct care to their young but can indirectly increase their offspring's success in host nests. One way in which parasitic Cowbirds (Molothrus sp.) could achieve this is through egg puncturing, whereby, prior to laying in a nest, females puncture the eggs that are already present in the nest to reduce the competition that their offspring will later face for food. In this study we investigated whether Cowbirds strategically increase their puncturing effort with increasing competitiveness of the future brood. We filmed egg-puncturing behaviour by shiny Cowbirds, Molothrus bonariensis, at nests of chalk-browed mockingbirds, Mimus saturninus, a large host whose nests often receive multiple Cowbird eggs. We presented Cowbirds with large (4 eggs) or small (1 egg) clutches of either mockingbird or Cowbird eggs, where large clutch sizes predict greater intrabrood competition than small clutch sizes, and mockingbird eggs (which are larger) predict greater competition than other Cowbird eggs. Cowbirds delivered more pecks and punctured more eggs per visit to larger clutches, and mockingbird eggs were broken more often than Cowbird eggs, but pecked less per visit. The higher number of pecks aimed at Cowbird eggs, despite these producing less competitive nestmates, could reflect responses to eggshell strength rather than egg size, as Cowbird eggs are harder to break because of their thicker shells and so require more effort to puncture. Our results show that Cowbird puncturing behaviour is not rigid and varies with nest contents. We suggest this variation is consistent with females increasing their offspring's chance of survival.
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Antiparasitic defenses in hosts of South American Cowbirds
Chinese Birds, 2013Co-Authors: Juan C Reboreda, Vanina D. Fiorini, María C. De MársicoAbstract:The Cowbirds (Molothrus, Icteridae) are a monophyletic group that includes five extant brood-parasitic species. The Screaming (M. rufoaxillaris), Giant (M. oryzivorus) and Shiny (M. bonar- iensis) Cowbirds range mostly in South America. Screaming and Shiny Cowbirds are the ancestral and most recent species of the clade, respectively, therefore, differing in how long they have coevolved with their hosts. We present new experimental data on egg-rejection in a host of the Shiny Cow- bird, the House Wren (Troglodytes aedon), review different lines of antiparasitic defenses in hosts of Screaming, Giant and Shiny Cowbirds and assess whether hosts of different parasites differ in the type and extent of defenses. Hosts of all three parasites ejected non-mimetic eggs. Most hosts of Giant and Shiny Cowbirds were grasp ejectors, whereas the main host of the Screaming Cowbird (the Baywing, Agelaioides badius) ejected parasitic eggs using its feet. Hosts smaller than Shiny Cowbirds neither ejected Cowbird eggs nor deserted nests following parasitism. Some hosts also reacted more aggres- sively towards the parasite. The main host of Screaming Cowbird discriminated against non-mimetic chicks. Our results show that most hosts, regardless of the presumed evolutionary time of interaction with the parasite, have evolved some type of antiparasitic defense.
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host parasite coevolution beyond the nestling stage mimicry of host fledglings by the specialist screaming Cowbird
Proceedings of The Royal Society B: Biological Sciences, 2012Co-Authors: María C. De Mársico, Mariela G Gantchoff, Juan C ReboredaAbstract:Egg mimicry by obligate avian brood parasites and host rejection of non-mimetic eggs are well-known textbook examples of host–parasite coevolution. By contrast, reciprocal adaptations and counteradaptations beyond the egg stage in brood parasites and their hosts have received less attention. The screaming Cowbird (Molothrus rufoaxillaris) is a specialist obligate brood parasite whose fledglings look identical to those of its primary host, the baywing (Agelaioides badius). Such a resemblance has been proposed as an adaptation in response to host discrimination against odd-looking young, but evidence supporting this idea is scarce. Here, we examined this hypothesis by comparing the survival rates of young screaming Cowbirds and non-mimetic shiny Cowbirds (Molothrus bonariensis) cross-fostered to baywing nests and quantifying the similarity in plumage colour and begging calls between host and Cowbird fledglings. Shiny Cowbirds suffered higher post-fledging mortality rates (83%) than screaming Cowbirds (0%) owing to host rejection. Visual modelling revealed that screaming Cowbirds, but not shiny Cowbirds, were indistinguishable from host young in plumage colour. Similarly, screaming Cowbirds matched baywings' begging calls more closely than shiny Cowbirds. Our results strongly support the occurrence of host fledgling mimicry in screaming Cowbirds and suggest a role of visual and vocal cues in fledgling discrimination by baywings.
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Reproductive Success and Nestling Growth of the Baywing Parasitized by Screaming and Shiny Cowbirds
The Wilson Journal of Ornithology, 2010Co-Authors: María C. De Mársico, Bettina Mahler, Juan C ReboredaAbstract:Abstract We studied the breeding biology of the Baywing (Agelaioides badius), a shared host of Screaming (Molothrus rufoaxillaris) and Shiny (M. bonariensis) Cowbirds. We monitored 193 nests from December 2002 to March 2007 in the Province of Buenos Aires, Argentina. Baywings used a wide variety of nesting sites, mainly old nests of furnarids. Their breeding season lasted from late November to February and was closely matched by that of Screaming Cowbirds. The breeding season for Shiny Cowbirds started in late September but overlapped that of Baywings. Frequency and intensity of Screaming Cowbird parasitism were 93% and 5 eggs per parasitized nest, while for Shiny Cowbirds they were 16% and 1.4 eggs. Host clutch size was 4.0 ± 0.1 eggs and did not vary with time of breeding. Weight at hatching and age of maximum growth were similar for host and Screaming Cowbird nestlings. Shiny Cowbird nestlings had higher weight at hatching and lower age of maximum growth than the other two species. Screaming and Shiny ...
Nancy E. Mathews - One of the best experts on this subject based on the ideXlab platform.
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Community-level patterns of population recruitment in a generalist avian brood parasite, the brown-headed Cowbird
Oecologia, 2010Co-Authors: David R. Curson, Christopher B. Goguen, Nancy E. MathewsAbstract:The brown-headed Cowbird ( Molothrus ater ) is a generalist brood parasite that typically parasitizes many host species in a single bird community. Population recruitment in a generalist parasite should be diverse with respect to host species; however, host-specific rates of Cowbird recruitment have not been reported in any host community, and the determinants of host quality are poorly known. We studied the combined influence of parasitism level, nest abundance, and host quality on community-level patterns of Cowbird recruitment in New Mexico, USA. Our objectives were to: (1) evaluate patterns of host use and quality; (2) compare Cowbird egg investment and recruitment among host species; (3) identify host species of most importance to Cowbird recruitment. Cowbirds parasitized 11 host species, with five “major” hosts experiencing high parasitism levels (≥1 Cowbird egg/nest) and six minor hosts experiencing low parasitism levels (
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community level patterns of population recruitment in a generalist avian brood parasite the brown headed Cowbird
Oecologia, 2010Co-Authors: David R. Curson, Christopher B. Goguen, Nancy E. MathewsAbstract:The brown-headed Cowbird (Molothrus ater) is a generalist brood parasite that typically parasitizes many host species in a single bird community. Population recruitment in a generalist parasite should be diverse with respect to host species; however, host-specific rates of Cowbird recruitment have not been reported in any host community, and the determinants of host quality are poorly known. We studied the combined influence of parasitism level, nest abundance, and host quality on community-level patterns of Cowbird recruitment in New Mexico, USA. Our objectives were to: (1) evaluate patterns of host use and quality; (2) compare Cowbird egg investment and recruitment among host species; (3) identify host species of most importance to Cowbird recruitment. Cowbirds parasitized 11 host species, with five “major” hosts experiencing high parasitism levels (≥1 Cowbird egg/nest) and six minor hosts experiencing low parasitism levels (<0.3 Cowbird eggs/nest). Parasitism level was not correlated with host species abundance, host mass, host nestling period length, or host success at fledging Cowbirds. However, tree-nesting hosts were parasitized more than ground-nesters, and foliage-gleaners more than sally-foragers and ground-foragers. Average estimated survival to fledging of Cowbird eggs laid in active host nests was 0.19. Cowbird recruitment was diverse with respect to hosts but was less evenly distributed across the host community than was Cowbird egg investment because western tanagers (Piranga ludovicianus) fledged Cowbirds more successfully than other hosts. This success in western tanagers was due to high Cowbird survivorship in tanager nests and may be associated with the larger body size of tanagers relative to other hosts.
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Reproductive costs of commuting flights in brown-headed Cowbirds
The Journal of Wildlife Management, 2003Co-Authors: David R. Curson, Nancy E. MathewsAbstract:Brood parasitism by brown-headed Cowbirds (Molothrus ater, hereafter Cowbird) has attracted much attention from conservation biologists as an edge effect over small spatial scales, reducing nesting success of songbirds near habitat boundaries. The mechanisms underlying this landscape-scale edge effect have not been studied, but this phenomenon has been attributed to the energetic costs of commuting by Cowbirds-i.e., daily flights between breeding and feeding areas. We studied Cowbird egg-laying rates by counting ovarian follicles at a site in New Mexico, USA, where previous research had established the presence of short-distance commuting (SDC; approx 2 km) and long-distance commuting (LDC; approx 12 km) Cowbirds. We hypothesized that LDG Cowbirds would lay fewer eggs than SDC Cowbirds and have more atretic yolky follicles (follicles degenerating prior to ovulation) due to the greater energetic demands of their commuting flights. In 1999-2000, we found that LDC Cowbirds had half the number of post-ovulatory follicles corresponding to a 5-day period (x = 1.8; n = 16) as SDC Cowbirds (x = 3.5, n = 14; P = 0.008). Thus, the egg-laying rate of LDC Cowbirds (0.36/day) was only half that of SDC Cowbirds (0.7/day). Long-distance commuting Cowbirds also had more atretic follicles (x = 1.3, n = 16; P = 0.006) than SDC (x = 0.2, n = 14), suggesting that the difference in egg-laying rates was due largely to energetic stress in Cowbirds commuting longer distances. Wing length and body mass were smaller in LDC Cowbirds than SDC Cowbirds, suggesting that LDC Cowbirds may have been subordinate individuals excluded from breeding habitat closer to feeding areas by intraspecific competition. These results suggest that management strategies, such as livestock removals, designed to reduce Cowbird numbers at host nest sites may provide additional benefits to hosts by reducing the fecundity of individual Cowbirds.
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brown headed Cowbird behavior and movements in relation to livestock grazing
Ecological Applications, 2001Co-Authors: Christopher B. Goguen, Nancy E. MathewsAbstract:The Brown-headed Cowbird (Molothrus ater) is a widespread brood parasite which often engages in a commensalistic feeding relationship with domestic livestock. We studied the behavior of female Cowbirds breeding in pinyon–juniper woodlands in New Mexico, USA, on two adjacent sites, one an active cattle ranch, and the other a site that was not grazed by domestic livestock throughout the songbird breeding season. In 1994, we conducted morning and afternoon surveys of Cowbird abundance in pinyon–juniper and prairie habitats; from 1995 to 1997 we used radio telemetry to monitor daily and seasonal movement and behavioral patterns of female Cowbirds. Our objectives were to measure how closely Cowbird feeding behavior was linked to livestock grazing, and how the presence or absence of active livestock grazing within a female's breeding range influenced diurnal patterns of behavior. During morning surveys, we detected Cowbirds primarily in pinyon–juniper habitat, but in similar numbers in the ungrazed and actively...
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Long-distance Commuting by Brown-headed Cowbirds in New Mexico
The Auk, 2000Co-Authors: David R. Curson, Christopher B. Goguen, Nancy E. MathewsAbstract:The Brown-headed Cowbird (Molothrus ater) is a widespread brood parasite that has attracted considerable recent attention as a possible threat to forestdwelling songbirds (e.g. Finch 1991, Robinson et al. 1995). Cowbirds are unusual among passerines in that their parasitic nature allows some populations to have spatially and temporally separate breeding and feeding activities (Rothstein et al. 1984). Cowbirds are ground foragers that feed in open habitats such as grazed grasslands, agricultural fields, livestock corrals, and mowed lawns (Friedmann 1929, Mayfield 1965, Ortega 1998). For breeding, however, Cowbirds occupy a wider variety of habitats where their passerine hosts occur in higher densities (Robinson et al. 1995). This reliance on distinct habitat types for essential activities gives rise to daily commuting patterns in landscapes where breeding and feeding habitats are spatially separated (Rothstein et al. 1984, Thompson 1994, Gates and Evans 1998). Cowbirds are restricted to parasitizing nests that are within commuting distances of their feeding habitats. In recent years, recognition of the relationship between feeding and breeding habitats of Cowbirds has led to management strategies involving the manipulation of feeding habitats to alter Cowbird breeding distributions for the benefit of potential hosts. For example, in the Coconino National Forest, Arizona, managers rotate livestock (which enhance feeding opportunities for Cowbirds) away from nesting sites of endangered Southwestern Willow Flycatchers (Empidonax traillii extimus; Goguen and Mathews 1999). For such strategies to effectively protect hosts, the scale at which they are implemented must be sufficient to discourage Cowbirds from commuting. The maximum commuting distance between breeding and feeding sites of Cowbirds is one of several factors needed to determine the correct scale of management efforts for Cowbirds. In previous radio-telemetry studies, the longest observed commute between breeding and feeding areas of female Cowbirds has been around 7 km (Rothstein et al. 1984, Thompson 1994, Gates and Evans 1998). This distance has been used as an estimate of the maximum commuting distance for female Cowbirds (e.g. Gustafson and Crow 1994, Coker and Capen 1995) and is the distance used for livestock removal in some Cowbird management efforts (e.g. Goguen and Mathews 1999). Given the conservation implications, it is necessary to
Stephen I. Rothstein - One of the best experts on this subject based on the ideXlab platform.
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the brown headed Cowbird a model species for testing novel research questions in animal ecology evolution and behavior
2017Co-Authors: Brian D. Peer, Scott K Robinson, James W Rivers, Loren Merrill, Stephen I. RothsteinAbstract:Although the brown-headed Cowbird (Molothrus ater) is the most intensively studied brood parasite in the world, much of the research on Cowbirds has focused on the negative effects of parasitism. Here, we argue that negative attitudes toward the Cowbird have overshadowed opportunities this species provides for advancing our understanding of social behavior, physiology, evolution, and ecology and conservation of birds. Cowbirds are widely distributed, amenable to captive study, and easy to study in areas where they are abundant. Cowbird nestlings must communicate to unrelated host parents, but unlike some parasitic nestlings, they have no specialized adaptations for doing so. In some areas they often share nests with relatives, which may influence the degree of virulence host experience. The generalist strategy of the Cowbird can be used to answer questions about the impact of high reproductive output on female Cowbirds, maternal allocation of resources into eggs, and the consequences of exposure to a range of pathogens while visiting host nests. Cowbirds and their hosts provide a contrast to cuckoo-host systems because they are at an earlier stage of coevolution, and only a minority of hosts shows effective defenses against parasitism. Cowbirds serve as a model species for studying song learning as aspects of their complex vocalizations are dependent on experience to different degrees. Cowbirds also challenge assumptions of the link between mating systems and parental care because Cowbirds are often socially monogamous. Finally, Cowbirds are unique among brood parasites for their effects on endangered host species. In this chapter, we discuss the value of Cowbirds as a model species in these areas and suggest avenues for future research.
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The Brown-headed Cowbird: North America's avian brood parasite
Chinese Birds, 2013Co-Authors: Brian D. Peer, James W Rivers, Stephen I. RothsteinAbstract:There are five species of parasitic Cowbirds ( Molothrus) and the Brown-headed Cowbird (M. ater) is the only widespread species in North America. The Brown-headed Cowbird is a host generalist and is typically found in open habitats and forest edges. The Cowbirds are of a more recent origin than many other brood parasites and perhaps as a result, Cowbird adaptations for parasitism and their hosts' counter-adaptations to thwart parasitism do not appear as sophisticated as those of other brood parasite-host systems. Because of its generalist nature, the Cowbird has the potential to negatively impact endangered host species whose populations are limited due to anthropogenic habi- tat loss. As a consequence, the Brown-headed Cowbird is one of the few brood parasitic species that is the subject of control programs to limit its effects on such hosts.
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Cowbirds, conservation, and coevolution: potential misconceptions and directions for future research
Chinese Birds, 2013Co-Authors: Brian D. Peer, James W Rivers, Stephen I. RothsteinAbstract:Avian brood parasitism is a model system for studies of coevolution and ecological interac- tions between parasites and their hosts. However, recent work may have led to misconceptions con- cerning the Brown-headed Cowbird (Molothrus ater), the most widely studied brood parasitic bird in the world, and its effects on host species. Potential misconceptions about this species that could affect management issues are as follows: Cowbird populations are increasing; Cowbirds are relatively new to North America; recently exposed hosts are defenseless against parasitism; Cowbirds have caused wide- spread declines of songbirds; and Cowbird control is always effective in increasing the size of endan- gered host populations. Potential coevolutionary misconceptions are that Cowbirds are typically "host tolerant"; Cowbirds evict host nestmates; and the mafia effect is widespread. It is important to clarify these issues because such misconceptions could hinder our understanding of parasite-host interac- tions, and thus obscure the direction of basic research and of management efforts taken to limit cow- bird impacts on endangered species. We discuss these issues and suggest future research directions to enhance our understanding of this fascinating species.
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brown headed Cowbird nestlings influence nestmate begging but not parental feeding in hosts of three distinct sizes
Animal Behaviour, 2010Co-Authors: James W Rivers, Thomas M Loughin, Stephen I. RothsteinAbstract:Avian brood parasites typically depress the fitness of their hosts by reducing the number of host offspring produced, yet little is known about how parasitic nestlings influence the behaviour of host parents and host offspring. In this study, we used three hosts of the brown-headed Cowbird, Molothrus ater, that varied in size (i.e. smaller, similar to and larger than Cowbirds of a given age) to determine whether parasitic nestlings altered patterns of food provisioning by host parents and begging by host young under field conditions. Adult provisioning did not change in the presence of a Cowbird but instead was influenced by feeding treatment and host size. In parasitized broods where nestlings differed in size (i.e. the small and large hosts), the larger nestling received the majority of food brought to the nest, regardless of whether it was the Cowbird or host nestling. In contrast, similar-sized host nestlings received a similar amount of food in parasitized and unparasitized host broods. Relative to unparasitized broods, the presence of a Cowbird led to increased begging intensity by the small host, had no clear effect on begging behaviour of the intermediate-sized host, and reduced begging intensity of the large host. Taken together, these results suggest the presence of a Cowbird did not lead to changes in provisioning behaviour in parents, and the extent to which Cowbirds influenced host begging behaviour depended on the size of the host.
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Parasitic Cowbirds may defeat host defense by causing rejecters to misimprint on Cowbird eggs
Behavioral Ecology, 2009Co-Authors: Bill M. Strausberger, Stephen I. RothsteinAbstract:Experiments suggest that some hosts that reject parasitic brown-headed Cowbird (Molothrus ater) eggs develop egg recognition by imprinting on their own eggs, probably at the first nest naive birds attend. This raises the possibility that parasitism of naive individuals might cause them to mistakenly misimprint on, and accept, Cowbird eggs. In an egg-learning experiment designed to cause misimprinting, hosts accepted Cowbird eggs when they had laid only 1 egg even though most rejected Cowbird eggs when nests had ≥2 host eggs. These findings show that Cowbirds can cause misimprinting by parasitizing naive hosts. If done opportunistically, misimprinting should become more likely as Cowbird abundance increases. In accord with this expectation, simulated brood parasitism showed that 3 host species that usually reject Cowbird eggs were more tolerant of Cowbird eggs in the Great Plains, where Cowbirds reach maximal historic abundance, than in eastern North America where Cowbirds are less common. This relation between parasite abundance and host responses is opposite to that found in cuckoo hosts. In addition, these 3 rejecter species had high rates (10.8--30.4%) of natural Cowbird parasitism at an Illinois site where Cowbirds are extremely, and historically, abundant. These rejecters accepted most cases of researcher-detected parasitism, even though they rarely accept where Cowbirds are less common. Despite the potentially high cost resulting from egg rejection, we demonstrate that parasitism of "rejecters" can be adaptive for Cowbirds particularly when host egg recognition involves learning. Copyright 2009, Oxford University Press.
Christopher B. Goguen - One of the best experts on this subject based on the ideXlab platform.
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Community-level patterns of population recruitment in a generalist avian brood parasite, the brown-headed Cowbird
Oecologia, 2010Co-Authors: David R. Curson, Christopher B. Goguen, Nancy E. MathewsAbstract:The brown-headed Cowbird ( Molothrus ater ) is a generalist brood parasite that typically parasitizes many host species in a single bird community. Population recruitment in a generalist parasite should be diverse with respect to host species; however, host-specific rates of Cowbird recruitment have not been reported in any host community, and the determinants of host quality are poorly known. We studied the combined influence of parasitism level, nest abundance, and host quality on community-level patterns of Cowbird recruitment in New Mexico, USA. Our objectives were to: (1) evaluate patterns of host use and quality; (2) compare Cowbird egg investment and recruitment among host species; (3) identify host species of most importance to Cowbird recruitment. Cowbirds parasitized 11 host species, with five “major” hosts experiencing high parasitism levels (≥1 Cowbird egg/nest) and six minor hosts experiencing low parasitism levels (
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community level patterns of population recruitment in a generalist avian brood parasite the brown headed Cowbird
Oecologia, 2010Co-Authors: David R. Curson, Christopher B. Goguen, Nancy E. MathewsAbstract:The brown-headed Cowbird (Molothrus ater) is a generalist brood parasite that typically parasitizes many host species in a single bird community. Population recruitment in a generalist parasite should be diverse with respect to host species; however, host-specific rates of Cowbird recruitment have not been reported in any host community, and the determinants of host quality are poorly known. We studied the combined influence of parasitism level, nest abundance, and host quality on community-level patterns of Cowbird recruitment in New Mexico, USA. Our objectives were to: (1) evaluate patterns of host use and quality; (2) compare Cowbird egg investment and recruitment among host species; (3) identify host species of most importance to Cowbird recruitment. Cowbirds parasitized 11 host species, with five “major” hosts experiencing high parasitism levels (≥1 Cowbird egg/nest) and six minor hosts experiencing low parasitism levels (<0.3 Cowbird eggs/nest). Parasitism level was not correlated with host species abundance, host mass, host nestling period length, or host success at fledging Cowbirds. However, tree-nesting hosts were parasitized more than ground-nesters, and foliage-gleaners more than sally-foragers and ground-foragers. Average estimated survival to fledging of Cowbird eggs laid in active host nests was 0.19. Cowbird recruitment was diverse with respect to hosts but was less evenly distributed across the host community than was Cowbird egg investment because western tanagers (Piranga ludovicianus) fledged Cowbirds more successfully than other hosts. This success in western tanagers was due to high Cowbird survivorship in tanager nests and may be associated with the larger body size of tanagers relative to other hosts.
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brown headed Cowbird behavior and movements in relation to livestock grazing
Ecological Applications, 2001Co-Authors: Christopher B. Goguen, Nancy E. MathewsAbstract:The Brown-headed Cowbird (Molothrus ater) is a widespread brood parasite which often engages in a commensalistic feeding relationship with domestic livestock. We studied the behavior of female Cowbirds breeding in pinyon–juniper woodlands in New Mexico, USA, on two adjacent sites, one an active cattle ranch, and the other a site that was not grazed by domestic livestock throughout the songbird breeding season. In 1994, we conducted morning and afternoon surveys of Cowbird abundance in pinyon–juniper and prairie habitats; from 1995 to 1997 we used radio telemetry to monitor daily and seasonal movement and behavioral patterns of female Cowbirds. Our objectives were to measure how closely Cowbird feeding behavior was linked to livestock grazing, and how the presence or absence of active livestock grazing within a female's breeding range influenced diurnal patterns of behavior. During morning surveys, we detected Cowbirds primarily in pinyon–juniper habitat, but in similar numbers in the ungrazed and actively...
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Long-distance Commuting by Brown-headed Cowbirds in New Mexico
The Auk, 2000Co-Authors: David R. Curson, Christopher B. Goguen, Nancy E. MathewsAbstract:The Brown-headed Cowbird (Molothrus ater) is a widespread brood parasite that has attracted considerable recent attention as a possible threat to forestdwelling songbirds (e.g. Finch 1991, Robinson et al. 1995). Cowbirds are unusual among passerines in that their parasitic nature allows some populations to have spatially and temporally separate breeding and feeding activities (Rothstein et al. 1984). Cowbirds are ground foragers that feed in open habitats such as grazed grasslands, agricultural fields, livestock corrals, and mowed lawns (Friedmann 1929, Mayfield 1965, Ortega 1998). For breeding, however, Cowbirds occupy a wider variety of habitats where their passerine hosts occur in higher densities (Robinson et al. 1995). This reliance on distinct habitat types for essential activities gives rise to daily commuting patterns in landscapes where breeding and feeding habitats are spatially separated (Rothstein et al. 1984, Thompson 1994, Gates and Evans 1998). Cowbirds are restricted to parasitizing nests that are within commuting distances of their feeding habitats. In recent years, recognition of the relationship between feeding and breeding habitats of Cowbirds has led to management strategies involving the manipulation of feeding habitats to alter Cowbird breeding distributions for the benefit of potential hosts. For example, in the Coconino National Forest, Arizona, managers rotate livestock (which enhance feeding opportunities for Cowbirds) away from nesting sites of endangered Southwestern Willow Flycatchers (Empidonax traillii extimus; Goguen and Mathews 1999). For such strategies to effectively protect hosts, the scale at which they are implemented must be sufficient to discourage Cowbirds from commuting. The maximum commuting distance between breeding and feeding sites of Cowbirds is one of several factors needed to determine the correct scale of management efforts for Cowbirds. In previous radio-telemetry studies, the longest observed commute between breeding and feeding areas of female Cowbirds has been around 7 km (Rothstein et al. 1984, Thompson 1994, Gates and Evans 1998). This distance has been used as an estimate of the maximum commuting distance for female Cowbirds (e.g. Gustafson and Crow 1994, Coker and Capen 1995) and is the distance used for livestock removal in some Cowbird management efforts (e.g. Goguen and Mathews 1999). Given the conservation implications, it is necessary to
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nest desertion by blue gray gnatcatchers in association with brown headed Cowbird parasitism
Animal Behaviour, 1996Co-Authors: Christopher B. Goguen, Nancy E. MathewsAbstract:The blue-gray gnatcatcher, Polioptila caerulea, is one of the smallest regular hosts of the brown-headed Cowbird, Molothrus ater. Gnatcatchers typically raise none of their own young when parasitized, yet anti-parasite behaviours have not been reported. A blue-gray gnatcatcher population in which pairs often desert nests when parasitized by Cowbirds was studied to examine the success of a desertion response and to determine factors that stimulate desertion. Of 83 gnatcatcher nests, 76% were parasitized; of nests parasitized during the egg-laying stage, 45% were deserted. Desertion occurred independently of the timing of the parasitism event during the breeding season and the number of Cowbird eggs laid per nest. All Cowbird eggs laid after the completion of the gnatcatcher's egg-laying stage were accepted. Parasitism rates were lower late in the breeding season, and nesting success of unparasitized nests was higher. Pairs that deserted often obtained Cowbird-free clutches, allowing them to raise gnatcatcher young. Nest desertion appears to be a means of avoiding parasitism and increasing fitness. The nest desertion response was inconsistent, but it cannot be explained by the adaptiveness of acceptance or by the possibility that blue-gray gnatcatchers are in transition between being acceptors or rejectors of Cowbird parasitism. Nest desertion by blue-gray gnatcatchers appears to be a generalized response to a disturbance at the nest induced by Cowbirds. The cue that elicits the desertion response remains unclear. ? 1996 The Association for the Study of Animal Behaviour
