Monday, July 14, 2025

Researchers use meteorological data to understand how climate and altitude affect bird migration

A first-of-its-kind international ecology study used weather radar to reveal that birds migrating through tropical regions travel at a steadier pace but with more variation in altitude compared to temperate regions.

University of Chicago Medical Center

Bird migration graphic — image:
*Migrating birds shown with spectrograms of the calls they use in flight, which researchers captured via acoustic monitoring complemented their radar data on migration patterns.*
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Credit: Jacob Drucker/University of Chicago

Every year, billions of birds undertake intrepid journeys between temperate regions in North America and their tropical wintering grounds in South America.

“Birds are great indicator species of environmental health, serving as bellwethers of global biodiversity gain and loss, so understanding their migration on a global scale is extremely important,” said Jacob Drucker, a doctoral student at the University of Chicago. “But until now, our knowledge of this massive natural phenomenon has been heavily biased towards temperate latitudes in North America and Europe.”

Drucker is the lead author of a first-of-its-kind international study that leveraged weather radar networks across Colombia to examine how migrating birds respond to different atmospheric conditions in the tropics compared to those in northern temperate zones. Their findings reveal how the relatively stable weather conditions of tropical climates shape bird migration in distinct ways that expand ecological understanding and could impact future conservation efforts.

How tropical winds change migration strategies

In temperate regions, predictable cycles of warm fronts and cold fronts make some nights much more favorable than others for the flight of migratory birds. As a result, bird migration in these areas typically happens in dramatic bursts, with huge numbers moving simultaneously during optimal wind conditions. In Colombia, those predictable cycles don't really exist; as a result, the researchers observed, birds migrate at a steadier, more gradual pace in tropical conditions.

“It turns out that wind isn't as important to birds in deciding which nights to fly in Colombia, but it plays a major role in deciding the altitude at which they fly,” Drucker said.

In the Colombian Andes, birds encounter consistent winds blowing southward at varying altitudes known as the Orinoco Low-level Jet. These winds act as helpful tailwinds for birds traveling south in the fall, but become headwinds in the spring. To conserve energy, birds adjust how high they fly to avoid the altitudes where the wind is blowing most strongly at any given time.

“We saw birds flying as high as 3,000 meters above the Amazon to avoid headwinds. It was spectacular,” Drucker said. “When the wind weakened at lower altitudes, birds adjusted by flying lower.”

International collaboration and innovative methods

This research was made possible through international collaboration with Colombian scientists and organizations, as well as experts from universities across the U.S. and Chicago’s Field Museum.

Seven years ago, Drucker approached several colleagues about using relatively new radar data from the IDEAM, Colombia’s national weather service. Together with Nick Bayly, director of migratory bird studies at Colombian nonprofit SELVA, and Alfonso Ladino, a meteorologist at the University of Champaign Urbana who previously worked with the IDEAM, he began building a project and partnership would lay the groundwork for unprecedented analysis of bird migration.

Other collaborators at Cornell University, including Drucker’s mentor Adriaan Dokter, PhD, played a critical role in developing advanced analytical methods to separate flocks of migrating birds from swarms of airborne insects — a significant methodological challenge in tropical environments.

“We initially struggled to distinguish between insects and birds,” Drucker recalled. “There are far more insects in the tropics, creating substantial radar noise from an ornithological perspective. To solve this, we built a model that assumes insects move passively with the wind, while birds move independently and purposefully.”

This approach, developed and validated using radar data from both Colombia and Australia, will also likely prove invaluable for future ecological research.

Conservation challenges in tropical cities

Understanding migration dynamics in Colombia has real-world conservation implications. Cities pose significant risks to migratory birds, especially through collisions with the windows of brightly-lit buildings at night.

In temperate regions, coordinated “lights out” campaigns timed with predictable large-scale migration events can help protect birds, but the new findings indicate that these approaches may face challenges in tropical cities like Bogotá, Medellín and Calí.

“Since bird migration in Colombia isn't tied to predictable wind events, it becomes much harder to anticipate large migration nights and tell people when to turn their lights off,” Drucker said. To effectively implement conservation measures, ecologists and policymakers will need to develop new strategies.

Looking ahead, Drucker emphasized the need for continued research to understand migration at even smaller scales.

“We need to drill down into the granular details of how birds react to specific habitats and finer-scale weather patterns along migration routes,” he said.

As scientists expand radar coverage and refine their methods, they are opening new avenues to protect migratory birds in a rapidly changing world.

“Stable atmospheric conditions underlie a steady pace of nocturnal bird migration in the tropics” was published in Proceedings of the Royal Society B in June 2025. Co-authors include Jacob Drucker, Benjamin Van Doren, Nicholas Bayly, Wilmer Ramirez, Alfonso Ladino Rincon, John Bates and Adriaan Dokter.

Journal

Proceedings of the Royal Society B Biological Sciences

DOI

10.1098/rspb.2024.2609

Method of Research

Data/statistical analysis

Subject of Research

Animals

Article Title

Stable atmospheric conditions underlie a steady pace of nocturnal bird migration in the tropics

Study discusses how to mitigate damage from gunshot injuries to the brain in children and young adults

Society of NeuroInterventional Surgery

FOR IMMEDIATE RELEASE: July 14, 2025

NASHVILLE — A study presented today at the Society of NeuroInterventional Surgery’s (SNIS) 22nd Annual Meeting found that almost half of gunshot wound injuries to the brain in children and young adults include penetrating cerebrovascular injuries (PCVIs). These types of injuries, which damage blood vessels in the brain and may result in high rates of permanent disability and death, may be mitigated if hospitals prioritize performing immediate vascular cranial imaging (tests that evaluate blood flow in the brain) and repeating these tests to check for changes.

Although gunshot injuries are now the leading cause of death for people under 25 in the United States, there has been little research into how PCVIs can be treated in children and young adults. In the study, “Penetrating Cerebrovascular Injuries in a Pediatric Cohort of Intracranial Gunshot Wounds: Incidence, Characterization of Injury Type, and Clinical Outcomes,” researchers at Louisiana State University aimed to fill in gaps in the research about identifying, categorizing and treating this type of devastating injury.

The scientists reviewed medical records for male patients ages 15–20 who were sent to a large city hospital between 2012–2021 with gunshot wounds to the brain. The team found that 38 patients underwent vascular imaging of the brain, of whom 17 individuals (44%) experienced PCVIs. Patients with PCVIs were more likely to die from their injuries than those without PCVIs (47.1% vs. 23.8%). Patients with PCVIs who survived their injuries were also more likely to experience severe permanent disability after treatment than those without PCVIs (76.2% vs. 41.2%).

“With gunshot injuries — including wounds to the head — becoming a tragically common occurrence in the U.S., it’s essential that we know more about how children’s and young adults’ brains are specifically impacted,” said Lucido L. Ponce Mejia, MD, a neurologist and neurocritical care specialist at Louisiana State University Health Sciences Center in New Orleans. “Performing vascular imaging on kids and young adults with gunshot wounds to the head early and often after these injuries take place can give us more information to improve care for these patients and potentially save lives.”

To receive a copy of this abstract or to speak with the study authors, please contact Camille Jewell at cjewell@vancomm.com or call 202-248-5460.

About the Society of NeuroInterventional Surgery

The Society of NeuroInterventional Surgery (SNIS) is a scientific and educational association dedicated to advancing the specialty of neurointerventional surgery through research, standard-setting, and education and advocacy to provide the highest quality of patient care in diagnosing and treating diseases of the brain, spine, head and neck. Visit www.snisonline.org and follow us on X (@SNISinfo) Facebook (@SNISOnline), LinkedIn (@Society of NeuroInterventional Surgery), Instagram (@SNIS_info) and Bluesky (@snisinfo.bsky.social).

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New research challenges animal dietary classifications in Yellowstone National Park

A federally funded analysis led by Brown University biologists found that different species of large herbivores have diets that are more diverse and complex than previously known.

Brown University

Bison family summer grazing — image:
A bison family grazes on flowers during the summer in the meadows of Yellowstone National Park.
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Credit: Photo courtesy of Hannah Hoff.

PROVIDENCE, R.I. [Brown University] — Scholars and schoolchildren alike have generally classified animals by the foods they eat: carnivores eat meat; browsers consume flowering plants, conifers and shrubs; and grazers focus on grasses.

But a new federally funded study led by Brown University biologists and scientists at Yellowstone National Park revealed that different circumstances lead herbivores to eat a much wider variety of plants than previously believed.

Published in the Proceedings of the National Academy of Sciences, the new research suggests that the traditional classification schemes that distinguish herbivores by their percent of grass consumption are oversimplifications that can fail to reflect dietary variation within and across species, said study co-author Tyler Kartzinel, an associate professor of ecology, evolution and organismal biology at Brown.

“This challenges biologists to consider whether we’re finding patterns in nature that reinforce our perceptions of what animals should be doing rather than what they are actually doing,” Kartzinel said. “It makes a very compelling case that in Yellowstone, we’re putting animals into boxes that include all members of a species but not considering the differences in eating behaviors within species or — perhaps more importantly — some of the similarities that unite different species.”

According to Kartzinel, this type of research can help scientists better anticipate the resources that wildlife use in changing landscapes where there are diverging opinions on conservation strategies.

“These findings are a big step toward understanding how so many species of large mammals can survive together in Yellowstone,” Kartzinel said. “Our findings suggest that maintaining plant diversity is a critical requirement for maintaining the diversity of migratory wildlife.”

When grazers become browsers

The research team has been studying animal foraging behaviors in Yellowstone for seven years. In a study published last year in Royal Society Open Science, the researchers focused on what the average member of herbivore species was doing to find food in Yellowstone.

In the new study, the team again collaborated with scientists at Yellowstone, who tracked animals from five herbivore species and collected fecal and plant samples. The species included pronghorn, bighorn sheep, mule deer, elk and bison. At Brown, researchers analyzed the samples using DNA metabarcoding, which helped to identify what plants the animals had consumed, and simple AI techniques to figure out how many different diet types exist within Yellowstone’s vast herds of wildlife and whether each species has its own unique diet type.

Study co-author Hannah Hoff, a Ph.D. candidate studying ecology, evolution and organismal biology at Brown, brought expertise in botany and data science to the project. Inspired by a seminar led by Brown University Professor of Biology and Data Science Sohini Ramachandran, Hoff incorporated machine learning in combination with genetic techniques to better understand herbivore behavior.

Dietary differences between species turned out to be smaller than previously assumed. Instead, researchers found that members of different species could have a lot of overlap in their diets and the amount of overlap depended on where and when they were feeding.

One of the team’s insights was that opportunity may drive foraging behavior more than animal species. In the summer, many animals from all species converged on a diet of nutritious wildflowers in the meadows of the summer range, while in the winter, a diet concentrated on coniferous trees and shrubs became more common.

During the winter, bison in particular, but not exclusively, tended to keep looking for grasses and similar types of food even when they were frozen under snow, while some of the smaller herbivores, like mule deer and pronghorn antelope, tended to switch more dramatically toward a diet of evergreen trees.

“It turns out the appropriate question is not, ‘Does that species eat grass?’” Kartzinel said, “but rather, ‘Is it eating grass right now?’”

As a plant ecologist, Hoff took a plant-forward approach to understanding this ecological community.

“There’s sometimes a tendency to treat vegetation as a static ‘habitat type,’ instead of as a dynamic set of interacting species with their own individual ecologies,” Hoff said. “Centering our analysis of diet groupings on the plant species that distinguished them allowed us to examine how seasonality, nutrition and spatial distribution influence herbivore foraging — insights that may be obscured by broad diet classifications.”

Kartzinel said the findings offer a lesson for scientists as well as iconoclastic animals.

“Imagine a herd of bison who are all supposed to be grazers, with one or two who want to eat like browsers,” Kartzinel said. “The traditional way that scientists would tell this story could be to dismiss the difference as aberrant or unimportant. But findings like this show us that dietary diversity actually is normal, and we should tell the story of the browsing bison, as well.”

This research was funded by the National Science Foundation (DEB-2046797, OIA-2033823) and the National Parks Service Cooperative Research and Trainings Program (P22AC00332-00, P23AC00378).