Collapse of a desert bird community over the past century driven by climate change

Climate change has caused deserts, already defined by climatic extremes, to warm and dry more rapidly than other ecoregions in the contiguous United States over the last 50 years. Desert birds persist near the edge of their physiological limits, and climate change could cause lethal dehydration and hyperthermia, leading to decline or extirpation of some species. We evaluated how desert birds have responded to climate and habitat change by resurveying historic sites throughout the Mojave Desert that were originally surveyed for avian diversity during the early 20th century by Joseph Grinnell and colleagues. We found strong evidence of an avian community in collapse. Sites lost on average 43% of their species, and occupancy probability declined significantly for 39 of 135 breeding birds. The common raven was the only native species to substantially increase across survey sites. Climate change, particularly decline in precipitation, was the most important driver of site-level persistence, while habitat change had a secondary influence. Habitat preference and diet were the two most important species traits associated with occupancy change. The presence of surface water reduced the loss of site-level richness, creating refugia. The collapse of the avian community over the past century may indicate a larger imbalance in the Mojave and provide an early warning of future ecosystem disintegration, given climate models unanimously predict an increasingly dry and hot future

Modeling effects of nonbreeders on population growth estimates

Acknowledgements We thank the Beissinger lab and reviewers for helpful comments on manuscript drafts. This research was funded by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (project NON- BREEDERS). The contents of this paper reflect the views of the researchers, not the views of the European Commission. Data Accessibility R-code available from the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.t56cn (Lee, Reid & Beissinger, 2016).Peer reviewedPostprin

Cooling requirements fueled the collapse of a desert bird community from climate change.

Climate change threatens global biodiversity by increasing extinction risk, yet few studies have uncovered a physiological basis of climate-driven species declines. Maintaining a stable body temperature is a fundamental requirement for homeothermic animals, and water is a vital resource that facilitates thermoregulation through evaporative cooling, especially in hot environments. Here, we explore the potential for thermoregulatory costs to underlie the community collapse of birds in the Mojave Desert over the past century in response to climate change. The probability of persistence was lowest for species occupying the warmest and driest sites, which imposed the greatest cooling costs. We developed a general model of heat flux to evaluate whether water requirements for evaporative cooling contributed to species' declines by simulating thermoregulatory costs in the Mojave Desert for 50 bird species representing the range of observed declines. Bird species' declines were positively associated with climate-driven increases in water requirements for evaporative cooling and exacerbated by large body size, especially for species with animal-based diets. Species exhibiting reductions in body size across their range saved up to 14% in cooling costs and experienced less decline than species without size reductions, suggesting total cooling costs as a mechanism underlying Bergmann's rule. Reductions in body size, however, are unlikely to offset the 50 to 78% increase in cooling costs threatening desert birds from future climate change. As climate change spreads warm, dry conditions across the planet, water requirements are increasingly likely to drive population declines, providing a physiological basis for climate-driven extinctions

Factors shaping the ontogeny of vocal signals in a wild parrot

Parrots rely heavily on vocal signals to maintain their social and mobile lifestyles. We studied vocal ontogeny in nests of wild green-rumped parrotlets (Forpus passerinus) in Venezuela. We identified three successive phases of vocal signaling that corresponded closely to three independently derived phases of physiological development. For each ontogenetic phase, we characterized the relative importance of anatomical constraints, motor skills necessary for responding to specific contexts of the immediate environment, and the learning of signals that are necessary for adult forms of communication. We observed shifts in the relative importance of these three factors as individuals progressed from one stage to the next; there was no single fixed ratio of factors that applied across the entire ontogenetic sequence. The earliest vocalizations were short in duration, as predicted from physical constraints and under-developed motor control. Calls became longer and frequency modulated during intermediate nestling ages in line with motor skills required for competitive begging. In the week before fledging, calls drastically shortened in accordance with the flight-constrained short durations of adult contact calls. The latter constraints were made evident by the demonstrated links between wing-assisted incline running, a widespread prelude to avian flight, just before the shift from long-duration begging calls to short-duration contact calls. At least in this species, the shifting emphases of factors at different ontogenetic stages precluded the morphing of intermediate-stage begging calls into adult contact calls; as shown previously, the latter are influenced by sample templates provided by parents

Avian Incubation Inhibits Growth and Diversification of Bacterial Assemblages on Eggs

Microbial infection is a critical source of mortality for early life stages of oviparous vertebrates, but parental defenses against infection are less well known. Avian incubation has been hypothesized to reduce the risk of trans-shell infection by limiting microbial growth of pathogenic bacteria on eggshells, while enhancing growth of commensal or beneficial bacteria that inhibit or competitively exclude pathogens. We tested this hypothesis by comparing bacterial assemblages on naturally incubated and experimentally unincubated eggs at laying and late incubation using a universal 16S rRNA microarray containing probes for over 8000 bacterial taxa. Before treatment, bacterial assemblages on individual eggs from both treatment groups were dissimilar to one another, as measured by clustering in non-metric dimensional scaling (NMDS) ordination space. After treatment, assemblages of unincubated eggs were similar to one another, but those of incubated eggs were not. Furthermore, assemblages of unincubated eggs were characterized by high abundance of six indicator species while incubated eggs had no indicator species. Bacterial taxon richness remained static on incubated eggs, but increased significantly on unincubated eggs, especially in several families of Gram-negative bacteria. The relative abundance of individual bacterial taxa did not change on incubated eggs, but that of 82 bacterial taxa, including some known to infect the interior of eggs, increased on unincubated eggs. Thus, incubation inhibits all of the relatively few bacteria that grow on eggshells, and does not appear to promote growth of any bacteria

Differential deposition of antimicrobial proteins in blue tit (Cyanistes caeruleus) clutches by laying order and male attractiveness

Female birds can influence offspring fitness by varying the relative quantities of egg components they deposit within and between clutches. Antimicrobial proteins (lysozyme, ovotransferrin, and avidin) are significant components of the avian albumen and likely aid in defense of embryos from microbial infection. Within clutches, females may enhance antimicrobial defense of early-laid eggs to protect them from the high risk of infection incurred before the onset of incubation. Among entire clutches, females may invest more resources in young sired by more attractive males because they have higher reproductive value. We tested these hypotheses by quantifying antimicrobial protein distribution within and among clutches in blue tit eggs. Contrary to our hypothesis, clutches showed no differential deposition of lysozyme or avidin within clutches, but eggs laid in the middle of the sequence had higher concentrations of ovotransferrin than eggs in the beginning and end. Consistent with our second hypothesis, we found that females produced eggs with higher concentrations of lysozyme (although not ovotransferrin or avidin) when mated to more attractive (more UV-reflective) males. Furthermore, females mated to polygynous males deposited less lysozyme than those mated to monogamous males. These data suggest that allocation of lysozyme at the clutch level may be a maternal effect mediated by male qualities

Beyond a warming fingerprint: individualistic biogeographic responses to heterogeneous climate change in California.

Understanding recent biogeographic responses to climate change is fundamental for improving our predictions of likely future responses and guiding conservation planning at both local and global scales. Studies of observed biogeographic responses to 20th century climate change have principally examined effects related to ubiquitous increases in temperature - collectively termed a warming fingerprint. Although the importance of changes in other aspects of climate - particularly precipitation and water availability - is widely acknowledged from a theoretical standpoint and supported by paleontological evidence, we lack a practical understanding of how these changes interact with temperature to drive biogeographic responses. Further complicating matters, differences in life history and ecological attributes may lead species to respond differently to the same changes in climate. Here, we examine whether recent biogeographic patterns across California are consistent with a warming fingerprint. We describe how various components of climate have changed regionally in California during the 20th century and review empirical evidence of biogeographic responses to these changes, particularly elevational range shifts. Many responses to climate change do not appear to be consistent with a warming fingerprint, with downslope shifts in elevation being as common as upslope shifts across a number of taxa and many demographic and community responses being inconsistent with upslope shifts. We identify a number of potential direct and indirect mechanisms for these responses, including the influence of aspects of climate change other than temperature (e.g., the shifting seasonal balance of energy and water availability), differences in each taxon's sensitivity to climate change, trophic interactions, and land-use change. Finally, we highlight the need to move beyond a warming fingerprint in studies of biogeographic responses by considering a more multifaceted view of climate, emphasizing local-scale effects, and including a priori knowledge of relevant natural history for the taxa and regions under study

Genetic factors in threatened species recovery plans on three continents

Around the world, recovery planning for threatened species is being applied in an attempt to stem the current extinction crisis. Genetic factors linked to small population processes (eg inbreeding, loss of genetic diversity) play a key role in species viability. We examined how often genetic factors are considered in threatened species recovery planning. We selected recent species recovery plans from Europe (n = 110), North America (the US only; n = 100), and Australia (n = 108), and reviewed three broad categories of genetic data they address: population-genetic, fitness-related, and life-history data. We found that the host country, taxonomic group to which the species belonged, and several proposed management actions were important predictors of the inclusion of genetic factors. Notably, species recovery plans from the US were more likely to include genetic issues, probably due to legislative requirements. We recommend an international standard, similar to an IUCN Red List framework, that requires explicit consideration of genetic aspects of long-term viability

Hardship at birth alters the impact of climate change on a long-lived predator

Climate change is increasing the frequency of extreme events, such as droughts or hurricanes, with substantial impacts on human and wildlife communities. Extreme events can affect individuals through two pathways: by altering the fitness of adults encountering a current extreme, and by affecting the development of individuals born during a natal extreme, a largely overlooked process. Here, we show that the impact of natal drought on an avian predator overrode the effect of current drought for decades, so that individuals born during drought were disadvantaged throughout life. Incorporation of natal effects caused a 40% decline in forecasted population size and a 21% shortening of time to extinction. These results imply that climate change may erode populations more quickly and severely than currently appreciated, suggesting the urgency to incorporate "penalties" for natal legacies in the analytical toolkit of impact forecasts. Similar double impacts may apply to other drivers of global change.</p