Heatwaves in southwestern US deserts leave songbirds at risk

The magnitude and duration of heatwaves in the desert of the southwestern United States are projected to put songbirds at a greater risk for death, according to research funded by the National Science Foundation.

The drastically high temperatures have caused fatal dehydration and mass death in five species of songbirds. The recurrence and strength of the heatwaves may change activity, the conservation standings and geographic location restraints of the impacted songbirds. The heatwaves are expected to further intensify under climate change.

Researchers analyzed the impact of heatwaves on evaporative water loss in songbirds. They focused on five songbird species frequently found in the southwest desert: the Abert’s towhee, the cactus wren, the curve-billed thrasher, the house finch and the lesser goldfinch.

Blair Wolf, a professor of biology at the University of New Mexico, examined the heat resistance for each of the five species and found that birds are vulnerable to heat stress for two reasons. Firstly, birds cannot evaporate enough water to stay refreshed, so they become overheated and perish from heat exhaustion. Secondly, the excessive amounts of evaporative water depletion needed to stay cool drains their body water pools to life-threatening quantities, causing them to die of dehydration.

Co-author Alexander Gerson, an assistant professor of biology at the University of Massachusetts Amherst, further explained that a songbird’s rate of water loss increases at about 40 degrees Celsius, or 104 degrees Fahrenheit. Most animals can only withstand water depletion that triggers a 15 or 20 percent loss of body mass before they die. Gerson clarified that an animal who encounters peak temperatures on a scorching summer day with no water will not live long.

Researchers utilized hourly geospatial temperature maps and mechanistically informed models created by North American Land Data Assimilation System, a land surface modeling effort that NASA maintains along with other organizations.

They used physiological statistics to analyze how amounts of evaporative water loss in reaction to high temperatures were different among five species with varying body masses. They further sought to see how frequently the temperature differs and how climate change affects die-offs. Using this information, researchers were able to pinpoint the impact of current and future heatwaves on fatal dehydration perils for songbirds and how fast dehydration can happen in each species.

The results found that smaller species are particularly in jeopardy because they lose water at a more rapid rate. Small-bodied birds are also more likely to experience destructive conditions more frequently, over shorter time periods and over wide-ranging geographic locations.

At 50 degrees Celsius, or 122 degrees Fahrenheit, the lesser goldfinch and the house finch lose 8 to 9 percent of their body mass to evaporative water loss per hour, whereas only 5 percent of a curve-billed thrasher’s mass is depleted per hour. By the end of the century, the amount of days in the southwest desert where fatal dehydration will be a noticeable hazard will rise from seven days to 25 days per year.

While house finches and lesser gold finches are smaller than their counterparts, they enjoy better endurance: the two species can thrive in a multitude of ecosystems and they cover more extensive territory. On the other hand, the curve-billed thrasher and Abert’s towhee have distinct environmental requirements that restrict where they could settle, confining them to deserts in the Southwest. This signifies that a considerable amount of their population is in danger of fatal dehydration when brutal heatwaves occur.

An increase in 4 degrees Celsius will increase the magnitude of dehydration perils and will stir new menaces for larger songbirds. Scientists anticipate a 7 degrees Fahrenheit increase between 2070 and 2100. As temperatures rise, species such as the cactus wren will disperse from states like Arizona and California and will become concentrated in Texas.

Researchers commented that microclimates such as mountaintops, trees and washes with shade act as climate sanctuaries for songbirds. These environments permit a songbird’s body temperature to cool to a healthy level. This may be vital in supervision programs for defenseless species, as Gerson clarifies that if a scientist recognizes the best microclimate for the birds then they will better understand the temperatures that are appropriate for the songbirds.

The temperatures and heat wave occurrences will disrupt the water equilibrium and geographic dispersal of acid-region birds. The examination highlights the dangers of high temperatures—especially for the lesser goldfinch and the house finch—and advises protection of warm habitats and water supply.