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Spencer G Sealy - One of the best experts on this subject based on the ideXlab platform.
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Egg laying in inappropriate nests by the Brown-Headed Cowbird ( Molothrus ater ): acts of parasitism or emergency egg dumping?
The Canadian Field-Naturalist, 2015Co-Authors: Spencer G SealyAbstract:The generalist, brood-parasitic Brown-Headed Cowbird ( Molothrus ater ) has been found to parasitize the nests of about 220 species, mostly passerine birds. Among the thousands of documented cases of parasitism are rare records of egg laying in nests in which the Cowbird stands no chance of success, because its diet or developmental strategy are incompatible with those of the “host” species. Forty-four nests of 16 such inappropriate host species are reviewed: 23 nests of nine precocial species (waterbirds and shorebirds) plus 21 nests of seven altricial species (a raptor, doves, cuckoos, a hummingbird, and a woodpecker). Two hypotheses explain inappropriate egg laying. In the “normal laying” hypothesis, Brown-Headed Cowbirds may lay dozens of eggs in nests they encounter, including the occasional inappropriate nest. In the “emergency laying” hypothesis, females, on discovering that a selected nest has failed, must lay or “dump” her eggs elsewhere, in nests of inappropriate hosts or already-parasitized nests of regular hosts. Support for either hypothesis will require electronic surveillance of movements of nest-searching and laying Brown-Headed Cowbirds to generate fine-scale spatial data that confirm whether parasitism on inappropriate nests occurs at the usual laying time for pre-selected nests (around sunrise) or later in the day if the chosen nest has failed and emergency laying is required.
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increased investigation of manipulated clutches suggests egg recognition without rejection in a brown headed Cowbird molothrus ater host the yellow warbler setophaga petechia
The Auk, 2012Co-Authors: Melanie F Guigueno, Spencer G SealyAbstract:ABSTRACT. Egg discrimination underlies the evolution of a host's ability to reject a brood parasite's egg, but some hosts do not reject if it is too costly or if the parasitic egg mimics the host egg. We examined cues used by the Yellow Warbler (Setophaga petechia), a host of the Brown-Headed Cowbird (Molothrus ater), in its decision to reject (bury or desert) experimentally parasitized clutches. Yellow Warblers that returned to nests after a model egg was added spent significantly more time peering at and probing their nest contents and shuffling than before eggs were added. Rejection probability increased with the proportion of time Yellow Warblers probed their nest contents after settling on their clutch. Accepters and rejecters, however, peered at or shuffled their eggs the same amount of time and visited the nest and probed its contents (before settling) the same number of times. Burial occurred at 29 of 144 nests (20.1%) experimentally parasitized with model Cowbird eggs, of which 14 nests survived ...
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functional morphology as a barrier to the evolution of grasp ejection in hosts of the brown headed Cowbird molothrus ater
Canadian Journal of Zoology, 2010Co-Authors: Spencer G Sealy, Todd J. Underwood, Justin L RasmussenAbstract:Acceptance of eggs of the Brown-Headed Cowbird (Molothrus ater (Boddaert, 1783)) by hosts is enigmatic because hosts usually raise fewer of their own young when parasitized. Ejection may not be adaptive for small hosts because they cannot eject Cowbird eggs efficiently. Grasp-ejection apparently has a negligible cost but requires a bill of a minimum length that is not known. In this study, we examined the limits of grasp-ejection of the American Robin (Turdus migratorius L., 1766) and the Gray Catbird (Dumetella carolinensis (L., 1766)). We determined the largest object width that each species is capable of grasping (limit width) by observing individuals grasping models larger than Cowbird eggs in 104 video-recorded ejections and one direct observation. We standardized the limit width to the tomial length of each species (limit ratio) and extrapolated to the width of a Cowbird egg to predict the minimum tomial length required for grasp-ejection. Our results suggest that the minimum tomial length required ...
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Gray Jays Accept Brown-Headed Cowbird Eggs
The Wilson Journal of Ornithology, 2009Co-Authors: Spencer G Sealy, Brian D. Peer, Dan StricklandAbstract:Abstract Results of simulated brood parasitism on five Gray Jay (Perisoreus canadensis) nests suggest acceptance of model Brown-Headed Cowbird (Molothrus ater) eggs. This finding is contrary to results of experimental parasitism on four other species of jays, also with little or no recent history of parasitism, which eject Cowbird eggs. Given that Gray Jays nest in the boreal forest and earlier in the season than Cowbirds initiate breeding, it may be that neither Gray Jays nor their congeners have been parasitized regularly in their evolutionary histories, which may explain acceptance of Cowbird parasitism.
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parameters of brown headed Cowbird molothrus ater egg discrimination in warbling vireos vireo gilvus
Journal of Avian Biology, 2006Co-Authors: Todd J. Underwood, Spencer G SealyAbstract:We examined which egg parameters warbling vireos Vireo gilvus use to discriminate Brown-Headed Cowbird Molothrus ater eggs and, by comparing our results to other studies, tested the prediction that ejecter species with eggs more similar in appearance to Cowbird eggs will be less tolerant of foreign eggs. In addition, we tested the hypothesis that egg characteristics influence the cost of ejection and probability of committing ejection errors. Warbling vireos ejected 100% of eggs with a Cowbird spot pattern and only spot pattern significantly influenced the probability of ejecting a foreign egg, whereas size and nest stage did not. Foreign eggs that differed in two parameters were not ejected significantly more than those that differed in one parameter. Thus, warbling vireos appear to be less tolerant of foreign eggs than species with eggs more divergent from Cowbird eggs. There was no significant difference in the number of vireo eggs that were damaged when foreign eggs of different sizes and spot patterns were ejected, which is counter to the assumptions of the evolutionary equilibrium hypothesis. Similarly, foreign egg characteristics did not significantly influence the probability of ejection errors. Finally, egg discrimination in warbling vireos appears to have evolved directly to counter Cowbird parasitism because all conspecific eggs switched into their nests were accepted.
Brian D. Peer - One of the best experts on this subject based on the ideXlab platform.
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nest sanitation does not elicit egg ejection in a brown headed Cowbird host
Animal Cognition, 2017Co-Authors: Brian D. PeerAbstract:Most passerine birds practice nest sanitation whereby they remove debris from their nest. Nest sanitation has been posited as a pre-adaptation for egg ejection by hosts of avian brood parasites. However, relatively few North American hosts of the brood parasitic Brown-Headed Cowbird (Molothrus ater) eject Cowbird eggs to the detriment of their fitness. In this study, I added either a piece of flagging tape or a pine cone bract scale along with an artificial Cowbird egg to nests of the red-winged blackbird (Agelaius phoeniceus) to determine whether the act of nest sanitation would elicit egg ejection. All red-winged blackbirds removed the debris within 24 h, but all individuals also accepted the Cowbird eggs and this rate of ejection did not differ from that in nests that only received a Cowbird egg. While nest cleaning and egg ejection are similar mechanically, they differ cognitively and egg ejection is not elicited in red-winged blackbirds during the act of removing debris from their nests.
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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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Mechanisms of egg recognition in Brown-Headed Cowbird hosts: the role of ultraviolet reflectance
Animal Behaviour, 2015Co-Authors: Virginia E. Abernathy, Brian D. PeerAbstract:One of the most effective adaptations to counter avian brood parasitism is rejection of the parasitic egg, yet relatively few hosts reject eggs of the Brown-Headed Cowbird, Molothrus ater. Studies have demonstrated that ultraviolet (UV; 300–400 nm) reflectance of eggs plays a role in egg rejection by hosts of parasitic cuckoos Cuculus spp. Only two studies have experimentally tested whether a Cowbird host utilizes UV light when making egg rejection decisions, and those studies found no evidence that UV light was a significant factor. We experimentally blocked the UV reflectance of one host egg in the clutches of three rejecter species: brown thrasher, Toxostoma rufum, American robin, Turdus migratorius, and grey catbird, Dumetella carolinensis, to determine whether they utilize UV reflectance when rejecting eggs. We also measured the UV reflectance of each species' eggs. All host species rejected more of their own UV-blocked eggs than they did control eggs, but brown thrashers were significantly more likely to reject their own UV-blocked eggs than were American robins and grey catbirds. Brown thrasher eggs also reflected significantly more UV light than both American robin and grey catbird eggs. Our results coupled with those from similar studies suggest that hosts with brighter UV-reflecting eggs should be more likely to reject UV-blocked eggs than hosts with duller UV-reflecting eggs. This is the first study to demonstrate that UV reflectance is a parameter used by hosts of the Brown-Headed Cowbird when rejecting eggs and further increases our understanding of the mechanisms of egg recognition in brood-parasitic hosts.
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effect of parasite to host egg ratio on egg rejection by a brown headed Cowbird host
The Auk, 2014Co-Authors: Karlien A Lang, Eric K. Bollinger, Brian D. PeerAbstract:ABSTRACT American Robins (Turdus migratorius) typically eject parasitic Brown-Headed Cowbird (Molothrus ater) eggs from their nests. In order to successfully remove parasitic eggs, robins must first differentiate between their eggs and foreign eggs, and then remove the foreign egg(s). Our primary objectives were to determine (1) whether the robins reject Cowbird eggs because they are in the minority (“discordancy hypothesis”) or because robins have learned the appearance of their own eggs regardless of whether they form the majority of eggs in the nest (“true egg recognition hypothesis”); and (2) whether the robin's ability to recognize its eggs and reject parasitic eggs was affected by the parasite-to-host egg ratio. We added artificial Cowbird eggs to robin nests to create 3 treatments: (1) a majority of robin eggs, (2) an equal number of robin and Cowbird eggs, and (3) a majority of Cowbird eggs. Parasite-to-host egg ratios were between 1:3 and 3:1. Robins ejected all Cowbird eggs at 88% of nests (51 o...
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intraclutch variation in egg appearance of brown headed Cowbird hosts
The Auk, 2014Co-Authors: Virginia E. Abernathy, Brian D. PeerAbstract:ABSTRACT Several species of avian brood parasites have evolved egg mimicry, which can interfere with host egg rejection. Parasitic egg mimicry may select for decreased intraclutch variation in host egg appearance to facilitate the recognition and rejection of parasitic eggs. This hypothesis has received scant attention in hosts of the Brown-Headed Cowbird (Molothrus ater) because the Cowbird apparently has not evolved mimetic eggs. Nonetheless, hosts with eggs similar in appearance to Cowbird eggs should minimize intraclutch variation to increase the likelihood of detecting parasitism. By contrast, there may be minimal selection pressure to reduce intraclutch variation in hosts with eggs that are divergent from Cowbird eggs. Using reflectance spectrometry, we compared the intraclutch variation between accepters and rejecters of 2 groups of host species: those with eggs similar in appearance to Cowbird eggs (white maculate eggs) and those with eggs that clearly diverge in appearance from Cowbird eggs (blue...
Nancy E. Mathews - One of the best experts on this subject based on the ideXlab platform.
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costs of multiple parasitism for an avian brood parasite the brown headed Cowbird molothrus ater
Canadian Journal of Zoology, 2011Co-Authors: Christopher B. Goguen, David R. Curson, Nancy E. MathewsAbstract:The Brown-Headed Cowbird (Molothrus ater (Boddaert, 1783)) is a generalist brood parasite that often lays into nests that contain conspecific eggs. Although it has often been assumed that this multiple parasitism reduces Cowbird sur- vival, this has rarely been evaluated. We measured Cowbird survival in nests of the Blue-gray Gnatcatcher (Polioptila caeru- lea (L., 1766)), Plumbeous Vireo (Vireo plumbeus Coues, 1866), and Western Tanager (Piranga ludoviciana (A. Wilson, 1811)) in New Mexico, USA. Our objectives were to measure the costs of intraspecific competition on Cowbird survival in multiply-parasitized nests, evaluate if these costs were related to host size, and to compare the costs of multiple parasitism relative to other mortality sources that occur over the entire nesting cycle. Intraspecific competition reduced Cowbird sur- vival during the nestling period in nests of all three hosts, and was of particular importance in nests of the two smaller hosts. When all sources of egg mortality were considered, however, the costs of multiple parasitism were small compared with the large effects of predation and nest desertion. Given that multiple parasitism reduces Cowbird egg survival, it is un- clear why Cowbirds multiply-parasitize. Possible explanations depend on an improved understanding of fecundity and level of host nest selectivity by female Cowbirds. Resume : Le vacher a tete brune (Molothrus ater (Boddaert, 1783)) est un parasite generaliste des couvees qui pond sou- vent dans des nids qui contiennent des œufs de sa propre espece. Bien qu'on ait souvent presume que ce parasitisme multi- ple reduit la survie des vachers, on a rarement evalue la situation. Nous avons mesure la survie des vachers dans des nids du gobemoucheron gris-bleu (Polioptila caerulea (L., 1766)), du vireo plombe (Vireo plumbeus Coues, 1866) et du tangara a tete rouge (Piranga ludoviciana (A. Wilson, 1811)) au Nouveau-Mexique, E.-U. Notre objectif est de mesurer le cout de la competition intraspecifique sur la survie des vachers dans des nids a parasitisme multiple, d'evaluer si ces couts sont re- lies a la taille de l'hote et de comparer les couts du parasitisme multiple aux autres sources de mortalite qui se produisent au cours de l'ensemble du cycle de nidification. La competition intraspecifique reduit la survie des vachers durant la periode de nidification dans les nids des trois hotes et est d'importance particuliere surtout dans les nids des deux hotes plus petits. Lorsqu'on tient compte de toutes les sources de mortalite des œufs, les couts du parasitisme multiple sont faibles par rapport aux grands effets de la predation et de l'abandon des nids. Puisque le parasitisme multiple reduit la survie des œufs des va- chers, il n'est pas clair pourquoi les vachers pratiquent le parasitisme multiple. Les explications possibles requierent une meilleure comprehension de la fecondite et du niveau de selection des nids des hotes chez les vachers femelles. (Traduit par la Redaction)
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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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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...
Mark E Hauber - One of the best experts on this subject based on the ideXlab platform.
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increased egg nest visual contrast does not induce egg ejection in the eastern phoebe sayornis phoebe an accepter host of the brood parasitic brown headed Cowbird molothrus ater
Journal of Comparative Psychology, 2019Co-Authors: Zachary Aidala, Bill M. Strausberger, Mark E HauberAbstract:Hosts of obligate brood parasitic birds can offset the costs of parasitism by rejecting foreign eggs. Like the vast majority of Brown-Headed Cowbird (Molothrus ater) hosts, the eastern phoebe (Sayornis phoebe) paradoxically incurs substantial fitness costs by accepting Cowbird parasitism. We investigated whether acceptance of Brown-Headed Cowbird eggs may be mediated via lack of recognition due to crypsis in eastern phoebe nests, and whether egg-rejection behavior could be induced by manipulating egg-nest visual contrast as a means of facilitating parasitic egg detection in an artificial parasitism experiment. We found that Brown-Headed Cowbird eggs have significantly lower achromatic, but not chromatic, visual contrast against the natural nest lining relative to phoebe eggs, suggesting that Cowbird eggs may be cryptic in the low ambient light environments of natural or artificial covered ledges where eastern phoebes tend to nest. We also found that despite successfully increasing egg-nest visual contrast in our treatment, eastern phoebes did not reject model parasitic eggs. Our findings are consistent with previous work showing that increased egg-nest visual contrasts do not increase parasitic egg discriminability and rejection in hosts of avian brood parasites. Because sensory modeling showed that eastern phoebes were predicted to be able to visually perceive natural and experimental parasitism events, these hosts are suggested to lack the cognitive flexibility necessary to reject dissimilar eggs in their nests. Future work should determine whether this and other accepter species can be made to reject parasitism by using a more diverse array of artificial egg stimuli. (PsycINFO Database Record (c) 2019 APA, all rights reserved).
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brood parasitic Cowbird nestlings use host young to procure resources
Science, 2004Co-Authors: Rebecca M. Kilner, Mark E Hauber, Joah R MaddenAbstract:Young brood parasites that tolerate the company of host offspring challenge the existing evolutionary view of family life. In theory, all parasitic nestlings should be ruthlessly self-interested and should kill host offspring soon after hatching. Yet many species allow host young to live, even though they are rivals for host resources. Here we show that the tolerance of host nestlings by the parasitic Brown-Headed Cowbird Molothrus ater is adaptive. Host young procure the Cowbird a higher provisioning rate, so it grows more rapidly. The Cowbird's unexpected altruism toward host offspring simply promotes its selfish interests in exploiting host parents.
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site selection and repeatability in brown headed Cowbird molothrus ater parasitism of eastern phoebe sayornis phoebe nests
Canadian Journal of Zoology, 2001Co-Authors: Mark E HauberAbstract:The reproductive success of obligate brood parasitic birds depends on their ability to seek out heterospecific nests. Some nests are more suitable for parasitism than others and, for example, parasitic females may benefit from laying eggs preferentially and repeatedly at safer sites. Observations on patterns of Brown-Headed Cowbird (Molothrus ater) parasitism on Eastern Phoebes (Sayornis phoebe) across 2 years suggested that parasitism occurred at above chance levels during the first rather than the second nesting attempts and at nests located under eaves rather than bridges. Previously parasitized nests were more likely to be parasitized again in the subsequent breeding season. Sites under eaves and bridges did not differ in whether Brown-Headed Cowbirds could be detected in the proximity of the nest. However, nests from first nesting attempts and nests under eaves were less likely to be lost as a result of structural failure of the Eastern Phoebe's mud nest. These data suggest that site discrimination b...
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Site selection and repeatability in Brown-Headed Cowbird (Molothrus ater) parasitism of Eastern Phoebe (Sayornis phoebe) nests
Canadian Journal of Zoology, 2001Co-Authors: Mark E HauberAbstract:The reproductive success of obligate brood parasitic birds depends on their ability to seek out heterospecific nests. Some nests are more suitable for parasitism than others and, for example, parasitic females may benefit from laying eggs preferentially and repeatedly at safer sites. Observations on patterns of Brown-Headed Cowbird (Molothrus ater) parasitism on Eastern Phoebes (Sayornis phoebe) across 2 years suggested that parasitism occurred at above chance levels during the first rather than the second nesting attempts and at nests located under eaves rather than bridges. Previously parasitized nests were more likely to be parasitized again in the subsequent breeding season. Sites under eaves and bridges did not differ in whether Brown-Headed Cowbirds could be detected in the proximity of the nest. However, nests from first nesting attempts and nests under eaves were less likely to be lost as a result of structural failure of the Eastern Phoebe's mud nest. These data suggest that site discrimination by Brown-Headed Cowbirds leads to adaptive patterns of parasitism among available Eastern Phoebe nests.
Christopher B. Goguen - One of the best experts on this subject based on the ideXlab platform.
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costs of multiple parasitism for an avian brood parasite the brown headed Cowbird molothrus ater
Canadian Journal of Zoology, 2011Co-Authors: Christopher B. Goguen, David R. Curson, Nancy E. MathewsAbstract:The Brown-Headed Cowbird (Molothrus ater (Boddaert, 1783)) is a generalist brood parasite that often lays into nests that contain conspecific eggs. Although it has often been assumed that this multiple parasitism reduces Cowbird sur- vival, this has rarely been evaluated. We measured Cowbird survival in nests of the Blue-gray Gnatcatcher (Polioptila caeru- lea (L., 1766)), Plumbeous Vireo (Vireo plumbeus Coues, 1866), and Western Tanager (Piranga ludoviciana (A. Wilson, 1811)) in New Mexico, USA. Our objectives were to measure the costs of intraspecific competition on Cowbird survival in multiply-parasitized nests, evaluate if these costs were related to host size, and to compare the costs of multiple parasitism relative to other mortality sources that occur over the entire nesting cycle. Intraspecific competition reduced Cowbird sur- vival during the nestling period in nests of all three hosts, and was of particular importance in nests of the two smaller hosts. When all sources of egg mortality were considered, however, the costs of multiple parasitism were small compared with the large effects of predation and nest desertion. Given that multiple parasitism reduces Cowbird egg survival, it is un- clear why Cowbirds multiply-parasitize. Possible explanations depend on an improved understanding of fecundity and level of host nest selectivity by female Cowbirds. Resume : Le vacher a tete brune (Molothrus ater (Boddaert, 1783)) est un parasite generaliste des couvees qui pond sou- vent dans des nids qui contiennent des œufs de sa propre espece. Bien qu'on ait souvent presume que ce parasitisme multi- ple reduit la survie des vachers, on a rarement evalue la situation. Nous avons mesure la survie des vachers dans des nids du gobemoucheron gris-bleu (Polioptila caerulea (L., 1766)), du vireo plombe (Vireo plumbeus Coues, 1866) et du tangara a tete rouge (Piranga ludoviciana (A. Wilson, 1811)) au Nouveau-Mexique, E.-U. Notre objectif est de mesurer le cout de la competition intraspecifique sur la survie des vachers dans des nids a parasitisme multiple, d'evaluer si ces couts sont re- lies a la taille de l'hote et de comparer les couts du parasitisme multiple aux autres sources de mortalite qui se produisent au cours de l'ensemble du cycle de nidification. La competition intraspecifique reduit la survie des vachers durant la periode de nidification dans les nids des trois hotes et est d'importance particuliere surtout dans les nids des deux hotes plus petits. Lorsqu'on tient compte de toutes les sources de mortalite des œufs, les couts du parasitisme multiple sont faibles par rapport aux grands effets de la predation et de l'abandon des nids. Puisque le parasitisme multiple reduit la survie des œufs des va- chers, il n'est pas clair pourquoi les vachers pratiquent le parasitisme multiple. Les explications possibles requierent une meilleure comprehension de la fecondite et du niveau de selection des nids des hotes chez les vachers femelles. (Traduit par la Redaction)
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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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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...
