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The green-up of vegetation in spring brings a pulse of food resources that many animals track during migration. However, green-up phenology is changing with climate change, posing an immense challenge for species that time their migrations to coincide with these resource pulses. We evaluated changes in green-up phenology from 2002 to 2021 in relation to the migrations of 150 Western-Hemisphere bird species using eBird citizen science data. We found that green-up phenology has changed within bird migration routes, and yet the migrations of most species align more closely with long-term averages of green-up than with current conditions. Changing green-up strongly influenced phenological mismatches, especially for longer-distance migrants. These results reveal that bird migration may have limited flexibility to adjust to changing vegetation phenology and emphasize the mounting challenge migratory animals face in following en route resources in a changing climate., Competing Interests: Competing interests statement:The authors declare no competing interest.

Global climate change is increasing the frequency and intensity of weather extremes, including severe droughts in many regions. Drought can impact organisms by inhibiting reproduction, reducing survival and abundance, and forcing range shifts. For birds, considering temporal scale by averaging drought-related variables over different time lengths (i.e., temporal grains) captures different hydrologic attributes which may uniquely influence food supplies, vegetation greenness/structure, and other factors affecting populations. However, studies examining drought impacts on birds often assess a single temporal grain without considering that different species have different life histories that likely determine the temporal grain of their drought response. Furthermore, while drought is known to influence bird abundance and drive between-year range shifts, less understood is whether it causes within-range changes in species distributions. Our objectives were to (a) determine which temporal grain of drought (if any) is most related to bird presence/absence and whether this response is species specific; and (b) assess whether drought alters bird distributions by quantifying probability of local colonization and extinction as a function of drought intensity. We used North American Breeding Bird Survey data collected over 16 years, generalized linear mixed models, and dynamic occupancy models to meet these objectives. Different bird species responded to drought at different temporal grains, with most showing the strongest signal at annual or near-annual grains. For all drought-responsive species, increased drought intensity at any temporal grain always correlated with decreased occupancy. Additionally, colonization/extinction analyses indicated that one species, the dickcissel (Spiza americana), is more likely to colonize novel areas within the southern/core portion of its range during drought. Considering drought at different temporal grains, along with hydrologic attributes captured by each grain, may better reveal mechanisms behind drought impacts on birds and other organisms, and therefore improve understanding of how global climate change impacts species and the landscapes they inhabit., (© 2019 John Wiley & Sons Ltd.)

Two fundamental issues in ecology are understanding what influences the distribution and abundance of organisms through space and time. While it is well established that broad-scale patterns of abiotic and biotic conditions affect organisms' distributions and population fluctuations, discrete events may be important drivers of space use, survival, and persistence. These discrete extreme climatic events can constrain populations and space use at fine scales beyond that which is typically measured in ecological studies. Recently, a growing body of literature has identified thermal stress as a potential mechanism in determining space use and survival. We sought to determine how ambient temperature at fine temporal scales affected survival and space use for a ground-nesting quail species (Colinus virginianus; northern bobwhite). We modeled space use across an ambient temperature gradient (ranging from -20 to 38 °C) through a maxent algorithm. We also used Andersen-Gill proportional hazard models to assess the influence of ambient temperature-related variables on survival through time. Estimated available useable space ranged from 18.6% to 57.1% of the landscape depending on ambient temperature. The lowest and highest ambient temperature categories (<-15 °C and >35 °C, respectively) were associated with the least amount of estimated useable space (18.6% and 24.6%, respectively). Range overlap analysis indicated dissimilarity in areas where Colinus virginianus were restricted during times of thermal extremes (range overlap = 0.38). This suggests that habitat under a given condition is not necessarily a habitat under alternative conditions. Further, we found survival was most influenced by weekly minimum ambient temperatures. Our results demonstrate that ecological constraints can occur along a thermal gradient and that understanding the effects of these discrete events and how they change over time may be more important to conservation of organisms than are average and broad-scale conditions as typically measured in ecological studies., (© 2016 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.)

In tallgrass prairie, disturbances such as grazing and fire can generate patchiness across the landscape, contributing to a shifting mosaic that presumably enhances biodiversity. Grassland birds evolved within the context of this shifting mosaic, with some species restricted to one or two patch types created under spatially and temporally distinct disturbance regimes. Thus, management-driven reductions in heterogeneity may be partly responsible for declines in numbers of grassland birds. We experimentally altered spatial heterogeneity of vegetation structure within a tallgrass prairie by varying the spatial and temporal extent of fire and by allowing grazing animals to move freely among burned and unburned patches (patch treatment). We contrasted this disturbance regime with traditional agricultural management of the region that promotes homogeneity (traditional treatment). We monitored grassland bird abundance during the breeding seasons of 2001-2003 to determine the influence of altered spatial heterogeneity on the grassland bird community. Focal disturbances of patch burning and grazing that shifted through the landscape over several years resulted in a more heterogeneous pattern of vegetation than uniform application of fire and grazing. Greater spatial heterogeneity in vegetation provided greater variability in the grassland bird community. Some bird species occurred in greatest abundance within focally disturbed patches, while others occurred in relatively undisturbed patches in our patch treatment. Henslow's Sparrow, a declining species, occurred only within the patch treatment. Upland Sandpiper and some other species were more abundant on recently disturbed patches within the same treatment. The patch burn treatment created the entire gradient of vegetation structure required to maintain a suite of grassland bird species that differ in habitat preferences. Our study demonstrated that increasing spatial and temporal heterogeneity of disturbance in grasslands increases variability in vegetation structure that results in greater variability at higher trophic levels. Thus, management that creates a shifting mosaic using spatially and temporally discrete disturbances in grasslands can be a useful tool in conservation. In the case of North American tallgrass prairie, discrete fires that capitalize on preferential grazing behavior of large ungulates promote a shifting mosaic of habitat types that maintain biodiversity and agricultural productivity.

Quantifying resource selection (an organism's disproportionate use of available resources) is essential to infer habitat requirements of a species, develop management recommendations, predict species responses to changing conditions, and improve our understanding of the processes that underlie ecological patterns. Because study sites, even within the same region, can differ in both the amount and the arrangement of cover types, our objective was to determine whether proximal sites can yield markedly different resource selection results for a generalist bird, northern bobwhite (Colinus virginianus). We used 5 years of telemetry locations and newly developed land cover data at two, geographically distinct but relatively close sites in the south‐central semi‐arid prairies of North America. We fit a series of generalized linear mixed models and used an information‐theoretic model comparison approach to identify and compare resource selection patterns at each site. We determined that the importance of different cover types to northern bobwhite is site‐dependent on relatively similar and nearby sites. Specifically, whether bobwhite selected for shrub cover and whether they strongly avoided trees, depended on the study site in focus. Additionally, the spatial scale of selection was nearly an order of magnitude different between the cover types. Our study demonstrates that—even for one of the most intensively studied species in the world—we may oversimplify resource selection by using a single study site approach. Managing the trade‐offs between practical, generalized conclusions and precise but complex conclusions is one of the central challenges in applied ecology. However, we caution against setting recommendations for broad extents based on information gathered at small extents, even for a generalist species at adjacent sites. Before extrapolating information to areas beyond the data collected, managers should account for local differences in the availability, arrangement, and scaling of resources. [ABSTRACT FROM AUTHOR]

Grasslands are inherently dynamic systems having developed with frequent disturbance from fire and grazing that varies in space and time to create heterogeneity. Today, many management practices emphasize the even use of grasslands by grazers and either no fire or uniform fires, resulting in grasslands that lack the variability in plant structure and composition to support the entire suite of grassland biodiversity. Previous research has suggested that the reintroduction of variable disturbance may be among the best conservation strategies for grassland birds, as these practices promote diversity and abundance of many species. However, the reintroduction of heterogeneity is taking place in the context of the continued development of grasslands for energy production, and the utility of heterogeneity based management practices may decline in fragmented landscapes. We investigated how fragmentation from oil and gas may constrain management efforts to promote biodiversity by evaluating changes in bird abundance with distance from roads and conventional oil wells across a gradient of times since fire. We found that time since fire was the primary driver of grassland bird distribution, with dickcissels, eastern meadowlark and grasshopper sparrows occurring in all vegetation patches, while Henslow's sparrows primarily occurred in patches that were greater than 13 months post-fire and upland sandpipers were mostly detected in recent burns. Further, Henslow's sparrows avoided oil wells for considerable distances, while eastern meadowlark was more abundant in areas close to oil wells in vegetation patches that were one-year post-fire. Grasshopper sparrows avoided roads in recent burns and dickcissels, and eastern meadowlarks were attracted to roads in patches that were recently burned and one-year post-fire, respectively. The restoration of heterogeneous fire regimes will benefit bird communities by creating variable vegetation structure that can support multiple grassland bird species; however, energy development has the potential to fragment grasslands for some species. [ABSTRACT FROM AUTHOR]

Behavioral adjustments and parental decisions during reproduction can influence the thermal environment at nests, yet our understanding into how environmental factors (i.e., temperature and precipitation) constrain an adult's ability to balance self-maintenance and incubation demands is limited. To expand our understanding of how species respond to environmental factors, we investigated the reproductive ecology of two ground-nesting species (northern bobwhite [ Colinus virginianus ] and scaled quail [ Callipepla squamata ]) in a region (i.e., the Southern Great Plains) prone to thermal variability (i.e., extreme hot and cold temperatures). Specifically, our objective was to examine how temperature and precipitation directly influenced behavioral adjustments (i.e., off-bout duration, frequency, and nest attentiveness) and parental decisions (i.e., nest site selection), and indirectly influenced nest fate. Overall, we found that parents chose to nest in sites that were significantly cooler in temperature than randomly selected sites, and parents further altered the thermal environment experienced by embryos through incubation behavior. Daily precipitation and average ambient temperature and/or their interaction best predicted incubation behaviors, yet each species differed in the timing (i.e., morning vs. evening), frequency, and duration of off-bouts. Furthermore, successful nests were associated with cooler nest site temperatures for bobwhite and warmer nest site temperatures for scaled quail. Our finding of relatively stable (35.5 °C) incubation temperature for developing embryos of both species suggests that ground-nesting birds are able to regulate microclimate through behavioral adjustments and parental decisions even under extreme temperature fluctuations. Nevertheless, the ability for a ground-nesting species to effectively modify behavioral adjustments and decisions may be altered during long periods of enhanced physiological and environmental stress. [ABSTRACT FROM AUTHOR]

Ecological niche models (ENMs) have increasingly been used to estimate the potential effects of climate change on species’ distributions worldwide. Recently, predictions of species abundance have also been obtained with such models, though knowledge about the climatic variables affecting species abundance is often lacking. To address this, we used a well-studied guild (temperate North American quail) and the Maxent modeling algorithm to compare model performance of three variable selection approaches: correlation/variable contribution (CVC), biological (i.e., variables known to affect species abundance), and random. We then applied the best approach to forecast potential distributions, under future climatic conditions, and analyze future potential distributions in light of available abundance data and presence-only occurrence data. To estimate species’ distributional shifts we generated ensemble forecasts using four global circulation models, four representative concentration pathways, and two time periods (2050 and 2070). Furthermore, we present distributional shifts where 75%, 90%, and 100% of our ensemble models agreed. The CVC variable selection approach outperformed our biological approach for four of the six species. Model projections indicated species-specific effects of climate change on future distributions of temperate North American quail. The Gambel’s quail (Callipepla gambelii) was the only species predicted to gain area in climatic suitability across all three scenarios of ensemble model agreement. Conversely, the scaled quail (Callipepla squamata) was the only species predicted to lose area in climatic suitability across all three scenarios of ensemble model agreement. Our models projected future loss of areas for the northern bobwhite (Colinus virginianus) and scaled quail in portions of their distributions which are currently areas of high abundance. Climatic variables that influence local abundance may not always scale up to influence species’ distributions. Special attention should be given to selecting variables for ENMs, and tests of model performance should be used to validate the choice of variables. [ABSTRACT FROM AUTHOR]

Deviations from typical environmental conditions can provide insight into how organisms may respond to future weather extremes predicted by climate modeling. During an episodic and multimonth heat wave event (i.e., ambient temperature up to 43.4°C), we studied the thermal ecology of a ground-dwelling bird species in Western Oklahoma, USA. Specifically, we measured black bulb temperature ( Tbb) and vegetation parameters at northern bobwhite ( Colinus virginianus; hereafter bobwhite) adult and brood locations as well as at stratified random points in the study area. On the hottest days (i.e., ≥39°C), adults and broods obtained thermal refuge using tall woody cover that remained on average up to 16.51°C cooler than random sites on the landscape which reached >57°C. We also found that refuge sites used by bobwhites moderated thermal conditions by more than twofold compared to stratified random sites on the landscape but that Tbb commonly exceeded thermal stress thresholds for bobwhites (39°C) for several hours of the day within thermal refuges. The serendipitous high heat conditions captured in our study represent extreme heat for our study region as well as thermal stress for our study species, and subsequently allowed us to assess ground-dwelling bird responses to temperatures that are predicted to become more common in the future. Our findings confirm the critical importance of tall woody cover for moderating temperatures and functioning as important islands of thermal refuge for ground-dwelling birds, especially during extreme heat. However, the potential for extreme heat loads within thermal refuges that we observed (albeit much less extreme than the landscape) indicates that the functionality of tall woody cover to mitigate heat extremes may be increasingly limited in the future, thereby reinforcing predictions that climate change represents a clear and present danger for these species. [ABSTRACT FROM AUTHOR]

Taking brood flush counts is a common sampling method that has been used for decades to estimate brood and chick survival in many gallinaceous bird species. However, brood survival estimates based upon flush counts may be biased because of low detection probabilities, occurrence of brood amalgamations, brood abandonment, and brooding adult mortality. Given that brood flush counts are still commonly used to estimate brood survival, and in some cases extrapolated to provide an estimate of chick survival, it is important to evaluate biases associated with this method. Therefore, we evaluated the use of brood flush counts to estimate brood survival of 2 gallinaceous birds: Northern Bobwhite ( Colinus virginianus) and Scaled Quail ( Callipepla squamata). To gain a better understanding of some of the mechanisms that may bias brood survival estimates, we radio-tagged Northern Bobwhite and Scaled Quail chicks (8-12 days old) and juveniles (4-6 weeks old) in 67 broods. We used radio-tagged chicks and juveniles to estimate and compare brood survival using 2 analysis methodologies. These methods included a telemetry method that relied upon radio-tagged chicks and a flush method that mimicked a brood flush count. In bobwhites, the brood survival estimates were higher with the telemetry-based estimate than with the flush estimate for both the 3-week chick (0.808 vs. 0.500) and 5-week juvenile (0.636 vs. 0.364). In Scaled Quail, the 2 brood survival estimates were similar at the chick (0.842 vs. 0.789) and juvenile (0.818 vs. 0.818) life stages. Because Scaled Quail have lower occurrences of brooding adult mortality and brood abandonment, flush counts provided a more accurate estimate of brood survival for Scaled Quail than for bobwhites. In situations where brood abandonment or brooding adult mortality is common, researchers using flush counts to investigate gallinaceous brood survival should consider the impact that these mechanisms may have on survival estimates. Los conteos visuales de puestas por medio de la técnica 'flush' (haciendo volar a las aves, para poder observar su puesta) es un método de muestreo común, que ha sido utilizado durante décadas para estimar la supervivencia de la puesta y de los pollos en muchas especies de aves gallináceas. Sin embargo, las estimaciones de supervivencia de las puestas con base en estos conteos pueden estar sesgadas debido a la baja probabilidad de detección, la confusión por la amalgamación de la puesta, el abandono de puesta, y la mortalidad de adultos en el momento de la crianza. Teniendo en cuenta que este tipo de conteo de crías es comúnmente usado para estimar la supervivencia de la puesta, y en algunos casos es extrapolado para estimar la supervivencia de los pollos, es importante evaluar los sesgos asociados con esta metodología. Por tanto, evaluamos el uso de esta técnica de conteo para estimar la supervivencia de las puestas de 2 aves gallináceas: el colín de Virginia o codorniz cotuí norteña ( Colinus virginianus) y la codorniz escamosa ( Callipepla squamata). Para comprender mejor algunos de los mecanismos que pueden sesgar las estimaciones de supervivencia de crías, radio-etiquetamos pollos de codorniz norteña y codorniz escamosa (de 8-12 días de edad) y a individuos juveniles (de 4-6 semanas de edad) en 67 puestas. Utilizamos pollos y juveniles radio-etiquetados para estimar y comparar la supervivencia de las puestas por medio de 2 métodos de análisis. Estos métodos incluyen 'telemetría' que se basa en pollos radio-etiquetados y un método que imita al conteo 'flush'. En las codornices, las estimaciones de supervivencia de pollos de 3 semanas y de los juveniles de 5 semanas fueron mayores utilizando la estimación basada en telemetría, tanto en pollos (0.808 vs 0.500) como en juveniles (0.636 vs 0.364). En la codorniz escamosa, las estimaciones de supervivencia de las puestas fueron similares en pollos (0.842 vs 0.789) y en juveniles (0.818 vs 0.818). Con una mortalidad baja de adultos criando y abandonos de puesta, los conteos 'flush' ofrecen una estimación más precisa de supervivencia para codornices escamosas que para codornices norteñas. En situaciones en las que ocurre abandono de puestas, o cuando la mortalidad de adultos es muy común, los investigadores que utilizan conteos 'flush' para estudiar la supervivencia de las puestas de gallináceas, deben considerar el impacto que estos mecanismos pueden tener en las estimaciones de supervivencia. [ABSTRACT FROM AUTHOR]

Presents a study which determined migrant-shorebird species compositions, abundances, migration chronologies, use of habitats, and feeding ecologies in the Playa Lakes Region of Texas during spring and fall migration. Description of the study area; Results; Management and research implications.