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Papers by Stephen Rothstein
Ornithological Monographs, 2005
ABSTRACT Brown-headed Cowbird (Molothrus ater; hereafter "cowbird") parasitism ... more ABSTRACT Brown-headed Cowbird (Molothrus ater; hereafter "cowbird") parasitism is costly to host fitness, especially for smaller hosts whose nestlings have to compete with larger cowbird nestlings that often hatch earlier. Those fitness costs select for a variety of host defenses, including inconspicuous nests, aggression toward cowbirds, deserting parasitized nests, burying cowbird eggs, and ejecting cowbird eggs from nests. Egg ejection is the most effective defense against parasitism, but there are only 30 hosts known to regularly eject cowbird eggs. Evolutionary lag is the most likely reason that relatively few hosts demonstrate ejection. However, once ejection evolves in a host, some evidence indicates that it is maintained for long periods of time, even in the absence of brood parasitism-which suggests that host communities are becoming increasingly resistant to parasitism over time. With progressively fewer naive hosts to exploit, cowbirds may specialize on just a few host species. Retention of host defenses is also important because cowbirds were probably more common in the past, when mammalian megafauna were present. As a result, not every newly exposed host population requires cowbird control programs, because many have maintained defenses after inheriting them from ancestors that were exposed to parasitism, making them well defended against new bouts of parasitism. Several hosts that are currently the focus of control programs demonstrate defenses against parasitism, and their populations have increased. We suggest that the time has come to relax control of some of those species, to determine whether they can sustain their populations in the presence of parasitism and to allow their natural defenses to increase, so that they will not be perpetually dependent on human intervention. /// El parasitismo de Molothrus ater es costoso en términos de la adecuación de sus hospederos, en especial de aquellos de pequeño tamaño cuyos pichones deben competir con los pichones de Molothrus más grandes que en general eclosionan más temprano. Estos costos en adecuación seleccionan en favor de varias defensas por parte de los hopederos, que incluyen: nidos inconspicuos, agredir a los Molothrus, abandonar los nidos parasitados, y enterrar o rechazar los huevos de M. ater del nido. El rechazo del huevo es la defensa más efectiva contra el parasitismo, pero se sabe que sólo 30 especies de hospederos rechazan regularmente los huevos de M. ater. El retraso evolutivo es la causa más probable para explicar porqué tan bajo número de hospederos demuestran rechazo. Sin embargo, una vez que el rechazo evoluciona en un hospedero, existe evidencia indicando que es mantenido por largo tiempo, aún en ausencia de parasitismo de cría. Este último fenómeno sugeriría que las comunidades de hospederos se estarían volviendo cada vez más resistentes al parasitismo. Con una progresión hacia un menor número de hospederos "inocentes" para explotar, los Molothrus pueden especializarse en unas pocas especies hospederas. La retención de las defensas en los hospederos es también importante porque los Molothrus fueron probablemente más abundantes en el pasado, cuando la megafauna de mamíferos estaba presente. En consecuencia, no todas las especies de hospederos recientemente expuestas al parasitismo por Molothrus requerirían de programas de manejo de Molothrus. Muchas de ellas podrían mantener defensas que habrían heredado de ancestros que si estuvieron expuestos al parasitismo, haciendo que estuvieran bien defendidas contra nuevos eventos de parasitismo. Varios hospederos que actualmente son centro de programas de control demostraron defensas contra el parasitismo, y sus poblaciones se han incrementado. Nosotros sugerimos que ha llegado el tiempo de relajar el control sobre algunas de dichas especies, y de esta manera determinar si pueden mantener sus poblaciones en presencia del parasitismo. Al mismo tiempo, se estaría permitiendo que sus defensas naturales se incrementaran, y de este modo, que no dependieran perpetuamente de la intervención humana.
Behavioral Ecology, Sep 25, 2015
Ecology and Management of Cowbirds and Their Hosts, 2000
Studies in Avian Biology
The incidence of Brown-headed Cowbird (Molothrus ater) parasitism of Southwestern Willow Flycatch... more The incidence of Brown-headed Cowbird (Molothrus ater) parasitism of Southwestern Willow Flycatchers (Empidonax traillii extimus) is highly variable, ranging from less than 10% at some sites to over 50% at others. Parasitism usually results in complete loss of flycatcher reproductive output because most parasitized nests are deserted or fledge only a cowbird, although birds that desert often renest. Despite the reduced reproductive output from individual flycatcher nests, it is not clear that cowbird parasitism affects Southwestern Willow Flycatcher population sizes. Cowbird control reduces parasitism rates and increases the reproductive output of Southwestern Willow Flycatchers, but there is no firm evidence yet that it has resulted in any increases of flycatcher populations or forestalled declines, suggesting that populations may be limited by other factors, such as habitat. Cowbird control may nevertheless be an appropriate management option because some populations may benefit a...
Encyclopedia of Biodiversity, 2013
The Wilson Journal of Ornithology
Human–Wildlife Interactions, 2020
The brown-headed cowbird (Molothrus ater; cowbird) is unique among North American blackbirds (Ict... more The brown-headed cowbird (Molothrus ater; cowbird) is unique among North American blackbirds (Icteridae) because it is managed to mitigate the negative effects on endangered songbirds and economic losses in agricultural crops. Cowbird brood parasitism can further affect species that are considered threatened or endangered due to anthropogenic land uses. Historically, cowbirds have often been culled without addressing ultimate causes of songbird population declines. Similar to other North American blackbirds, cowbirds depredate agricultural crops, albeit at a lower rate reported for other blackbird species. Conflicting information exists on the extent of agricultural damage caused by cowbirds and the effectiveness of mitigation measures for application to management. In this paper, we reviewed the progress that has been made in cowbird management from approximately 2005 to 2020 in relation to endangered species. We also reviewed losses to the rice (Oryza sativa) crop attributed to co...
ABSTRACT The fate of host defensive behaviour in the absence of selection from brood parasitism i... more ABSTRACT The fate of host defensive behaviour in the absence of selection from brood parasitism is critical to long-term host-parasite coevolution. We investigated whether New World Bohemian waxwings Bombycilla garrulus that are allopatric from brown-headed cowbird Molothrus ater and common cuckoo Cuculus canorus parasitism have retained egg rejection behaviour. We found that egg rejection was expressed by 100 per cent of Bohemian waxwings. Our phylogeny revealed that Bohemian and Japanese waxwings Bombycilla japonica were sister taxa, and this clade was sister to the cedar waxwing Bombycilla cedrorum. In addition, there was support for a split between Old and New World Bohemian waxwings. Our molecular clock estimates suggest that egg rejection may have been retained for 2.8-3.0 Myr since New World Bohemian waxwings inherited it from their common ancestor with the rejecter cedar waxwings. These results support the 'single trajectory' model of host-brood parasite coevolution that once hosts evolve defences, they are retained, forcing parasites to become more specialized over time.
Ecology and Management of Cowbirds and Their Hosts, 2000
Ecology and Management of Cowbirds and Their Hosts, 2000
The Wilson Bulletin, 1987
Ornithological Monographs, 2005
ABSTRACT Brown-headed Cowbird (Molothrus ater; hereafter "cowbird") parasitism ... more ABSTRACT Brown-headed Cowbird (Molothrus ater; hereafter "cowbird") parasitism is costly to host fitness, especially for smaller hosts whose nestlings have to compete with larger cowbird nestlings that often hatch earlier. Those fitness costs select for a variety of host defenses, including inconspicuous nests, aggression toward cowbirds, deserting parasitized nests, burying cowbird eggs, and ejecting cowbird eggs from nests. Egg ejection is the most effective defense against parasitism, but there are only 30 hosts known to regularly eject cowbird eggs. Evolutionary lag is the most likely reason that relatively few hosts demonstrate ejection. However, once ejection evolves in a host, some evidence indicates that it is maintained for long periods of time, even in the absence of brood parasitism-which suggests that host communities are becoming increasingly resistant to parasitism over time. With progressively fewer naive hosts to exploit, cowbirds may specialize on just a few host species. Retention of host defenses is also important because cowbirds were probably more common in the past, when mammalian megafauna were present. As a result, not every newly exposed host population requires cowbird control programs, because many have maintained defenses after inheriting them from ancestors that were exposed to parasitism, making them well defended against new bouts of parasitism. Several hosts that are currently the focus of control programs demonstrate defenses against parasitism, and their populations have increased. We suggest that the time has come to relax control of some of those species, to determine whether they can sustain their populations in the presence of parasitism and to allow their natural defenses to increase, so that they will not be perpetually dependent on human intervention. /// El parasitismo de Molothrus ater es costoso en términos de la adecuación de sus hospederos, en especial de aquellos de pequeño tamaño cuyos pichones deben competir con los pichones de Molothrus más grandes que en general eclosionan más temprano. Estos costos en adecuación seleccionan en favor de varias defensas por parte de los hopederos, que incluyen: nidos inconspicuos, agredir a los Molothrus, abandonar los nidos parasitados, y enterrar o rechazar los huevos de M. ater del nido. El rechazo del huevo es la defensa más efectiva contra el parasitismo, pero se sabe que sólo 30 especies de hospederos rechazan regularmente los huevos de M. ater. El retraso evolutivo es la causa más probable para explicar porqué tan bajo número de hospederos demuestran rechazo. Sin embargo, una vez que el rechazo evoluciona en un hospedero, existe evidencia indicando que es mantenido por largo tiempo, aún en ausencia de parasitismo de cría. Este último fenómeno sugeriría que las comunidades de hospederos se estarían volviendo cada vez más resistentes al parasitismo. Con una progresión hacia un menor número de hospederos "inocentes" para explotar, los Molothrus pueden especializarse en unas pocas especies hospederas. La retención de las defensas en los hospederos es también importante porque los Molothrus fueron probablemente más abundantes en el pasado, cuando la megafauna de mamíferos estaba presente. En consecuencia, no todas las especies de hospederos recientemente expuestas al parasitismo por Molothrus requerirían de programas de manejo de Molothrus. Muchas de ellas podrían mantener defensas que habrían heredado de ancestros que si estuvieron expuestos al parasitismo, haciendo que estuvieran bien defendidas contra nuevos eventos de parasitismo. Varios hospederos que actualmente son centro de programas de control demostraron defensas contra el parasitismo, y sus poblaciones se han incrementado. Nosotros sugerimos que ha llegado el tiempo de relajar el control sobre algunas de dichas especies, y de esta manera determinar si pueden mantener sus poblaciones en presencia del parasitismo. Al mismo tiempo, se estaría permitiendo que sus defensas naturales se incrementaran, y de este modo, que no dependieran perpetuamente de la intervención humana.
Behavioral Ecology, Sep 25, 2015
Ecology and Management of Cowbirds and Their Hosts, 2000
Studies in Avian Biology
The incidence of Brown-headed Cowbird (Molothrus ater) parasitism of Southwestern Willow Flycatch... more The incidence of Brown-headed Cowbird (Molothrus ater) parasitism of Southwestern Willow Flycatchers (Empidonax traillii extimus) is highly variable, ranging from less than 10% at some sites to over 50% at others. Parasitism usually results in complete loss of flycatcher reproductive output because most parasitized nests are deserted or fledge only a cowbird, although birds that desert often renest. Despite the reduced reproductive output from individual flycatcher nests, it is not clear that cowbird parasitism affects Southwestern Willow Flycatcher population sizes. Cowbird control reduces parasitism rates and increases the reproductive output of Southwestern Willow Flycatchers, but there is no firm evidence yet that it has resulted in any increases of flycatcher populations or forestalled declines, suggesting that populations may be limited by other factors, such as habitat. Cowbird control may nevertheless be an appropriate management option because some populations may benefit a...
Encyclopedia of Biodiversity, 2013
The Wilson Journal of Ornithology
Human–Wildlife Interactions, 2020
The brown-headed cowbird (Molothrus ater; cowbird) is unique among North American blackbirds (Ict... more The brown-headed cowbird (Molothrus ater; cowbird) is unique among North American blackbirds (Icteridae) because it is managed to mitigate the negative effects on endangered songbirds and economic losses in agricultural crops. Cowbird brood parasitism can further affect species that are considered threatened or endangered due to anthropogenic land uses. Historically, cowbirds have often been culled without addressing ultimate causes of songbird population declines. Similar to other North American blackbirds, cowbirds depredate agricultural crops, albeit at a lower rate reported for other blackbird species. Conflicting information exists on the extent of agricultural damage caused by cowbirds and the effectiveness of mitigation measures for application to management. In this paper, we reviewed the progress that has been made in cowbird management from approximately 2005 to 2020 in relation to endangered species. We also reviewed losses to the rice (Oryza sativa) crop attributed to co...
ABSTRACT The fate of host defensive behaviour in the absence of selection from brood parasitism i... more ABSTRACT The fate of host defensive behaviour in the absence of selection from brood parasitism is critical to long-term host-parasite coevolution. We investigated whether New World Bohemian waxwings Bombycilla garrulus that are allopatric from brown-headed cowbird Molothrus ater and common cuckoo Cuculus canorus parasitism have retained egg rejection behaviour. We found that egg rejection was expressed by 100 per cent of Bohemian waxwings. Our phylogeny revealed that Bohemian and Japanese waxwings Bombycilla japonica were sister taxa, and this clade was sister to the cedar waxwing Bombycilla cedrorum. In addition, there was support for a split between Old and New World Bohemian waxwings. Our molecular clock estimates suggest that egg rejection may have been retained for 2.8-3.0 Myr since New World Bohemian waxwings inherited it from their common ancestor with the rejecter cedar waxwings. These results support the 'single trajectory' model of host-brood parasite coevolution that once hosts evolve defences, they are retained, forcing parasites to become more specialized over time.
Ecology and Management of Cowbirds and Their Hosts, 2000
Ecology and Management of Cowbirds and Their Hosts, 2000
The Wilson Bulletin, 1987