Anthropogenic climate change and habitat loss pose major threats to grassland breeding birds, the most rapidly declining group of birds in continental North America. Although previous studies have investigated grassland breeding bird responses to land management, few empirical studies explore their responses to climatic variation or its interactions with land management, which warrant urgent conservation attention. We evaluated the effects of climate and land management parameters on an indicator species for grassland breeding birds, the Grasshopper Sparrow (Ammodramus savannarum), a Neotropical migrant of conservation concern whose global population has declined by more than two thirds since 1970. We quantified Grasshopper Sparrow responses to climate variation, land management actions, and their interactions in the Platte River Valley, Nebraska, in the North American Great Plains, using six years of mark-recapture data collected via the Monitoring Avian Productivity and Survivorship (MAPS) protocol. We implemented generalized linear mixed models to estimate avian population trends (adult abundance and productivity) in response to changes in precipitation and temperature as well as cattle grazing, haying, and prescribed burning. Our models showed that climatic variation, especially spring precipitation, was the most important driver of avian population trends. Grasshopper Sparrow abundance declined with increasing spring precipitation, but prescribed burns helped mitigate this effect and were positively related to productivity, especially during years of lower spring temperatures. Our findings demonstrate the vulnerability of grassland bird population trends to ongoing and predicted climate change as well as the potential of land management actions to mitigate some negative effects of climate change on grassland breeding birds. Conséquences du changement climatique et de la gestion des terres sur un passereau migrateur néotropical en diminution dans les Grandes Plaines d'Amérique du Nord RÉSUMÉ. Les changements climatiques d'origine anthropique et la perte d'habitat constituent des menaces majeures pour les oiseaux de prairie nicheurs, groupe d'espèces qui diminue le plus rapidement en Amérique du Nord continentale. Bien que des études antérieures aient examiné les réactions des oiseaux de prairie nicheurs suivant la gestion des terres, peu d'études empiriques ont exploré leurs comportements à la suite de variations climatiques ou leurs interactions avec l'aménagement des terres, qui méritent pourtant une attention urgente pour la conservation. Nous avons évalué les effets du climat et des paramètres de gestion des terres sur une espèce représentative des oiseaux de prairie nicheurs, le Bruant sauterelle (Ammodramus savannarum), un migrateur néotropical dont la population mondiale a diminué de plus des deux tiers depuis 1970. Nous avons quantifié les réactions des Bruants sauterelles aux variations climatiques, aux mesures de gestion des terres et à leurs interactions dans la vallée de la rivière Platte, au Nebr...

Social organization as a topic has wide application often conserved across lineages and can lead to complex cultures, yet it is still not well understood in many taxa. We observed American bison (Bison bison) to investigate the interactions of hierarchy and behavior to elucidate patterns of social organization. Bison are highly visible animals that live in relatively accessible grasslands, and most are in semi-wild conservation herds that allows for access to low-stress observation and physiological exams. We observed behaviors in a semi-wild, reintroduced herd of 53 bison in a 140-ha prairie from April to October 2015 (165 h of observation). After establishing a linear hierarchy, we categorized individuals of each sex as high, mid-, or low ranking and then evaluated behavioral trends across rank and sex. We found that high ranking males constantly defended their linear positions and focused breeding efforts on the females with the highest productivity, consistent with disruptive sex characteristics. Intra-rank conflict focused on linear positioning likely causes the volatility in male bison hierarchy and stress of domination. Female bison, however, tend to suppress the lowest class, which likely drives their hierarchy's stability and stress of subordination. Our results show that male and female bison are impacted differently by their social rankings and show that individual aggressive actions may provide feedback loops to their social organization.

Few empirical studies have quantified relationships between changing weather and migratory songbirds, but such studies are vital in a time of rapid climate change. Climate change has critical consequences for avian breeding ecology, geographic ranges, and migration phenology. Changing precipitation and temperature patterns affect habitat, food resources, and other aspects of birds’ life history strategies. Such changes may disproportionately affect species confined to rare or declining ecosystems, such as temperate grasslands, which are among the most altered and endangered ecosystems globally. We examined the influence of changing weather on the dickcissel (Spiza americana), a migratory songbird of conservation concern that is an obligate grassland specialist. Our study area in the North American Great Plains features high historic weather variability, where climate change is now driving higher precipitation and temperatures as well as higher frequencies of extreme weather events including flooding and droughts. Dickcissels share their breeding grounds with brown-headed cowbirds (Molothrus ater), brood parasites that lay their eggs in the nests of other songbirds, reducing dickcissel productivity. We used 9 years of capture-recapture data collected over an 18-year period to test the hypothesis that increasing precipitation on dickcissels’ riparian breeding grounds is associated with abundance declines and increasing vulnerability to cowbird parasitism. Dickcissels declined with increasing June precipitation, whereas cowbirds, by contrast, increased. Dickcissel productivity appeared to be extremely low, with a 3:1 ratio of breeding male to female dickcissels likely undermining reproductive success. Our findings suggest that increasing precipitation predicted by climate change models in this region may drive future declines of dickcissels and other songbirds. Drivers of these declines may include habitat and food resource loss related to flooding and higher frequency precipitation events as well as increased parasitism pressure by cowbirds. Positive correlations of June-July precipitation, temperature, and time since grazing with dickcissel productivity did not mitigate dickcissels’ declining trend in this ecosystem. These findings highlight the importance of empirical research on the effects of increasing precipitation and brood parasitism vulnerability on migratory songbird conservation to inform adaptive management under climate change.

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Among the most rapidly declining birds in continental North America, grassland birds evolved with American bison (Bison bison) until bison nearly became extinct due to overhunting. Bison populations have subsequently rebounded due to reintroductions on conservation lands, but the impacts of bison on grassland nesting birds remain largely unknown. We investigated how bison reintroduction, together with other land management and climate factors, affected breeding populations of a grassland bird species of conservation concern, the Bobolink (Dolichonyx oryzivorus). We quantified population changes in Bobolinks over an 18-year period in conservation grasslands where bison were reintroduced, compared with adjacent grasslands grazed by cattle and where hay was harvested after the bird breeding season. Four years after bison reintroduction, the bison population in the study area had doubled, while Bobolink abundance declined 62% and productivity declined 84%. Our findings suggest that bison reintroduction as a conservation strategy may be counterproductive in grassland fragments where overgrazing, trampling, and other negative impacts drive declines in grassland breeding birds. Where bird conservation is an objective, small grassland reserves may therefore be inappropriate sites for bison reintroduction. To maximize conservation benefits to birds, land managers should prioritize protecting grassland birds from disturbance during the bird breeding season.