Friday, June 13, 2025

Study reveals why birds sing more at dawn in tropical forests

Cornell University

Ithaca, NY— New research published today in the journal Philosophical Transactions of the Royal Society B finds that territorial behavior and diet help explain why some birds sing more often at dawn.

Scientists from the Cornell Lab of Ornithology’s K. Lisa Yang Center for Conservation Bioacoustics and Project Dhvani in India studied 69 bird species in India's Western Ghats mountain range, one of the world's biodiversity hotspots, to understand why birds sing more or less at different times of the day.

To collect the data, the team placed microphones throughout the forest to automatically record bird vocalizations throughout the day—technology often referred to as passive acoustic monitoring. This technology records audio that researchers later listen to and catalogue which species vocalized during the day. “Passive acoustic monitoring allowed us to collect simultaneous acoustic data for 43 locations, over several months. We could not have done this study without it because we needed a lot of data to answer our questions,” said lead author Vijay Ramesh, postdoctoral researcher at the K. Lisa Yang Center for Conservation Bioacoustics.

The team found that 20 bird species had substantially higher vocal activity at dawn compared to dusk. These dawn singers included species such as Gray-headed Canary-Flycatcher, Greater Racket-tailed Drongo, and Large-billed Leaf Warbler. Only one species, the Dark-fronted Babbler, sang more often at dusk than dawn.

Ramesh and his colleagues examined four possible theories to explain why several of the species they studied sang more at dawn compared to dusk. Existing theories suggest that dawn singing is more prevalent due to microclimate conditions such as wind speed and air temperature that would allow birds with high-pitched songs to be heard more clearly over longer distances. Other theories suggest that birds sing more at dawn to defend their territories or to maximize foraging opportunities later in the day when there is more light, or more insect activity. The team gathered additional data from existing literature such as degree of territoriality and diet to examine these four theories alongside the acoustic data they collected in the field.

“We found that highly territorial birds and omnivorous species were much more likely to be active singers during dawn hours," said Ramesh. Singing in the early morning hours, the authors suggest, is important for territorial species to advertise and protect their locations. Species that eat insects and fruit (i.e., omnivores) also showed prevalence for singing more at dawn. Ramesh suspects omnivores might sing more at dawn because these species are often members of mixed-species foraging flocks where vocal communication is essential for finding food and for warning group members about potential predators nearby. But Ramesh says additional research that includes visual observations is needed to confirm his speculation.

The other environmental factors the team examined such as light levels and sound transmission conditions did not significantly influence when birds sang, challenging previous theories about why birds tend to vocalize more at dawn.

"Our findings demonstrate that social factors, particularly territoriality and feeding habits, are more important in driving dawn singing behavior than environmental conditions," Ramesh said.

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Reference: Ramesh, V., P. Sundar, M. P. Srivathsa, L. B. Symes. (2025). Why is the early bird early? An evaluation of hypotheses for avian dawn-biased vocal activity. Philosophical Transactions of the Royal Society B https://doi.org/10.1098/rstb/380/1928.

Journal

Philosophical Transactions of the Royal Society B Biological Sciences

DOI

10.1098/rstb/380/1928.

Method of Research

Survey

Subject of Research

Animals

Article Title

Why is the early bird early? An evaluation of hypotheses for avian dawn-biased vocal activity

Article Publication Date

12-Jun-2025

Wet soils increase flooding during atmospheric river storms

A new study examined decades of atmospheric river storms across the West Coast to pinpoint the conditions that lead to catastrophic flooding

Desert Research Institute

image:
Snapshot of the simulated landfall of an atmospheric river along the west coast of North America on February 11, 2020. Credit: DOE Office of Science, Energy Exascale Earth System Model (E3SM) project.
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Credit: DOE Office of Science

Atmospheric rivers are responsible for most flooding on the West Coast of the U.S., but also bring much needed moisture to the region. The size of these storms doesn’t always translate to flood risk, however, as other factors on the ground play important roles. Now, a new study helps untangle the other drivers of flooding to help communities and water managers better prepare.

The research, published June 4 in the Journal of Hydrometeorology, analyzed more than 43,000 atmospheric river storms across 122 watersheds on the West Coast between 1980 and 2023. The researchers found that one of the primary driving forces of flooding is wet soils that can’t absorb more water when a storm hits. They showed that flood peaks were 2-4.5 times higher, on average, when soils were already wet. These findings can help explain why some atmospheric river storms cause catastrophic flooding while others of comparable intensity do not. Even weaker storms can generate major floods if their precipitation meets a saturated Earth, while stronger storms may bring needed moisture to a parched landscape without causing flooding.

“The main finding comes down to the fact that flooding from any event, but specifically from atmospheric river storms, is a function not only of the storm size and magnitude, but also what’s happening on the land surface,” said Mariana Webb, lead author of the study who is completing her Ph.D. at DRI and the University of Nevada, Reno. “This work demonstrates the key role that pre-event soil moisture can have in moderating flood events. Interestingly, flood magnitudes don’t increase linearly as soil moisture increases, there's this critical threshold of soil moisture wetness above which you start to see much larger flows.”

The study also untangled the environmental conditions of regions where soil moisture has the largest influence on flooding. In arid places like California and southwestern Oregon, storms that hit when soils are already saturated are more likely to cause floods. This is because watersheds in these regions typically have shallow, clay-rich soils and limited water storage capacity. Due to lower precipitation and higher evaporation rates, soil moisture is also more variable in these areas. In contrast, in lush Washington and the interior Cascades and Sierra Nevada regions, watersheds tend to have deeper soils and snowpack, leading to a higher water storage capacity. Although soil saturation can still play a role in driving flooding in these areas, accounting for soil moisture is less valuable for flood management because soils are consistently wet or insulated by snow.

“We wanted to identify the watersheds where having additional information about the soil moisture could enhance our understanding of flood risk,” Webb said. “It’s the watersheds in more arid climates, where soil moisture is more variable due to evaporation and less consistent precipitation, where we can really see improvements in flood prediction.”

Although soil moisture data is currently measured at weather monitoring stations like the USDA’s SNOTEL Network, observations are relatively sparse compared to other measures like rainfall. Soil moisture can also vary widely within a single watershed, so often multiple stations are required to give experts a clear picture that can help inform flooding predictions. Increased monitoring in watersheds identified as high-risk, including real-time soil moisture observations, could significantly enhance early warning systems and flood management as atmospheric rivers become more frequent and intense.

By tailoring flood risk evaluations to a specific watershed’s physical characteristics and climate, the study could improve flood-risk predictions. The research demonstrates how flood risk increases not just with storm size and magnitude, but with soil moisture, highlighting the value of integrating land surface conditions into impact assessments for atmospheric rivers. “My research really focuses on this interdisciplinary space between atmospheric science and hydrology,” Webb said. “There’s sometimes a disconnect where atmospheric scientists think about water up until it falls as rain, and hydrologists start their work once the water is on the ground. I wanted to explore how we can better connect these two fields.”

Webb worked with DRI ecohydrologist Christine Albano to produce the research, building on Albano’s extensive expertise studying atmospheric rivers, their risks, and their impacts on the landscape.

“While soil saturation is widely recognized as a key factor in determining flood risk, Mari’s work helps to quantify the point at which this level of saturation leads to large increases in flood risk across different areas along the West Coast,” Albano said. “Advances in weather forecasting allow us to see atmospheric rivers coming toward the coast several days before they arrive. By combining atmospheric river forecast information with knowledge of how close the soil moisture is to critical saturation levels for a given watershed, we can further improve flood early warning systems.”

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More information: The full study, Wet Antecedent Soil Moisture Increases Atmospheric River Streamflow Magnitudes Nonlinearly, is available from the Journal of Hydrometeorology at https://doi.org/10.1175/JHM-D-24-0078.1

Study authors include: Mariana Webb (DRI), Christine Albano (DRI), Adrian Harpold (UNR), Daniel Wagner (USGS), and Anna Wilson (UCSD)

About DRI

We are Nevada’s non-profit research institute, founded in 1959 to empower experts to focus on science that matters. We work with communities across the state — and the world — to address their most pressing scientific questions. We’re proud that our scientists continuously produce solutions that better human and environmental health.  

Scientists at DRI are encouraged to follow their research interests across the traditional boundaries of scientific fields, collaborating across DRI and with scientists worldwide. All faculty support their own research through grants, bringing in nearly $5 to the Nevada economy for every $1 of state funds received. With more than 600 scientists, engineers, students, and staff across our Reno and Las Vegas campuses, we conducted more than $52 million in sponsored research focused on improving peoples’ lives in 2024 alone.

At DRI, science isn’t merely academic — it’s the key to future-proofing our communities and building a better world. For more information, please visit www.dri.edu.

A conceptual diagram illustrating how wet soils can lead to storm flooding.

Credit

Mariana Webb/DRI