Big Brains And Ranges May Not Save Birds From Climate

A pioneering new research finds that even birds with big brains and large breeding ranges can be more susceptible to climate change than thought before. The research, carried out by scientists at The University of Texas at Austin and published in Nature Communications, contradicts the common assumptions about bird adaptability and shows how complicated the relationship is between behavior, geography, and climate.

Traditionally, conservationists have tended to equate wider geographic ranges and larger populations with decreased extinction threats. Likewise, birds with greater brain size—frequently assumed to be more behaviorally flexible—have been assumed to be more capable of surviving shifts in the environment. But this new study tells a more complex story, indicating that such characteristics do not necessarily ensure resilience.

The scientists analyzed worldwide distribution data for about 1,500 bird species with extensive range maps based on hundreds of thousands of bird records submitted by amateur scientists using the eBird database, an enormous online repository of bird records. Their investigation found a counterintuitive pattern: several birds that have wide geographic ranges in fact exist in tight climate niches. That is, even though they cover huge areas, the variety of climate conditions that they can adapt to is very narrow.

This makes a lot of sense in a region such as the Arctic, where the area is immense but climate conditions are quite uniform. As such, birds like the Bohemian waxwing, which has breeding habitats stretching over much of the Arctic region, might well be thought widespread and secure in their populations, yet they remain extremely specialized in adaptation to very limited climatic parameters. Major change in those conditions would result in severe jeopardization of survival. Conversely, the chestnut-crowned laughingthrush, a species found in a smaller area within the mountainous regions of Nepal and Bhutan, has a more varied range of climate types within its restricted geographic area—perhaps conferring a benefit when confronted with shifting climates.

It's a false assumption, says Carlos Botero, associate professor of integrative biology and the senior author on the paper, in that the particular vulnerabilities brought on by specialization to climate are ignored. "Since many of those species specialize to a very limited range of climates, those ostensibly large populations can be really vulnerable to collapse once climate conditions start to shift," Botero said.

Adding another twist to the study's findings is brain size. The scientists discovered that birds with big brains in relation to their body size—often linked with high behavioral flexibility—are, counterintuitively, usually climate specialists. Though such birds can display flexible behavior for foraging or nesting, they are able to survive only in specific climate conditions, and as a result, they turn out to be surprisingly sensitive to temperature and precipitation changes.

To measure climate vulnerability, the group built a novel framework that charted global climates according to two important metrics: "temperature harshness," the measure of how cold, fluctuating, and unpredictable an area is, and "xeric harshness," the monitor of dryness and rainfall fluctuation. Each species' climate preferences were then graphed on a two-dimensional climate space. This enabled them to see the width and severity of each bird's climate niche. Birds that live in narrow, extreme niches—particularly those at the periphery of the climate space—were more vulnerable.

These results imply that conservation approaches need to look beyond traditional checklists of risk factors like brain size, population size, or range size. Botero urged a more integrated strategy that considers the intricate interactions of several ecological and behavioral variables. "We need to quit examining individual risk factors in isolation, but assess how these multifaceted factors interact," he said. "Often, it is the non-obvious interactions that are most important."

The paper, co-written by João Fabrício Mota Rodrigues, a one-time postdoctoral researcher at UT Austin, highlights the importance of citizen science in contemporary ecological research. Through the use of massive amounts of data provided by birdwatchers across the globe, scientists can now study patterns that were out of reach before.

With the accelerating pace of climate change, this study is a timely reminder that assumptions about resilience are not necessarily universal. Conservation will have to take into account not only where species reside, but how narrowly they are specialized to the climates within those areas. Only by recognizing these unseen vulnerabilities can we hope to safeguard the birds that fill our skies today.