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Friday, December 05, 2025

Birds move higher up mountains as the climate warms

University of Helsinki

Infograph on bird elevation on mountains — image:
Bird species are shifting to higher elevations over time, likely in response to climate change. The red line represents the mean elevation of birds, which has moved uphill after 20 years.
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Credit: Image and image processing: Jani Närhi

Many bird species have moved toward colder areas in the mountains of Europe as the climate has warmed over the past two decades. Sunny southern slopes attract birds to live at higher elevations than do shadier northern slopes.

A new study examined 177 bird species in four large mountain ranges: the Alps, the Pyrenees, the Scandinavian Mountains, and the British Highlands. Of these species, 63 per cent moved uphill. This uphill movement has averaged about half a metre per year in the 2000s.

The fastest change happened in Scandinavia and the Alps — for example, the northern wheatear has shifted an average of 33 metres uphill in the Scandinavian mountains since 2001. No significant uphill shift was observed in Great Britain or the Pyrenees. This indicates that the causes behind range shifts, such as the intensity of climate change and human land use, vary from region to region.

In mountainous areas, local climatic conditions, or microclimates, can vary considerably even over short distances. For example, the northern mountain sides receive less sunlight than the southern sides, resulting in cooler and wetter conditions. These differences affect the habitats of species.

"Sunny slopes attract birds to higher elevations because vegetation zones and food resources are located higher up. However, birds are also moving uphill at the same rate on shady slopes, which suggests that warming temperatures are affecting the entire mountain landscape", explains PhD researcher Joséphine Couet from the Finnish Museum of Natural History, University of Helsinki.  

The results show that broader climatic trends are driving birds to move uphill in the mountains across Europe. Slopes that are less exposed to solar radiation could serve as refuges, but these small-scale advantages are not enough to counteract large-scale uphill movements.  

"Mountain areas are not only majestic landscapes, but also hotspots of biodiversity, home to many species that depend on specific climatic and habitat conditions. This information is crucial for conservation planning in complex terrains where local conditions vary greatly", Couet emphasizes.  

The study was published in the journal Global Ecology and Biogeography and is based on bird monitoring data from eight European countries between 2001 and 2021.

Northern Wheatear

Credit

Jani Närhi

Journal

Global Ecology and Biogeography

DOI

10.1111/geb.70143

Article Title

Solar Radiation Affects Bird Distributions but Not Elevational Shifts in European Mountains

Visual system of butterflies changes with seasons

An analysis of Buckeye butterflies finds that they aren’t just changing colors with the seasons but changing the way they see on a physiological level

University of Arkansas

The shift from warm summer to cool fall conditions can be stressful for many animals. Surviving each season requires a multitude of different physiological and behavioral traits that scientists are still working to understand.

One of the more obvious ways that animals respond to seasonal conditions is by changing their coloration to better suit the time of year. The common buckeye butterfly (Junonia coenia) has been of scientific interest for over a hundred years because of the stark contrast between summer adults that emerge with light wings and fall adults that emerge with dark wings. One explanation for the darker coloration is that it helps increase body temperature in cooler weather, as does the increase in time spent basking to soak up sunshine.

A team of researchers led by the University of Arkansas, in collaboration with Cornell University, wanted to see if they could connect these two seasonal changes with genetic changes underlying the butterflies’ visual systems. Ulitmately, they hoped to confirm that seasonal change in wing color is also accompanied by changes in behavior and sensitivities to certain colors, since color vision informs many butterfly behaviors.

The team caught and recorded the behavior of common buckeyes in northwest Arkansas prairies (specifically Woolsey, Chesney and Stump prairies) from May to November between 2018 and 2021. From eye tissue obtained from captured butterflies, they examined how patterns of gene expression differed between dark fall butterflies and light summer butterflies. They found that compared to light summer butterflies, darker fall butterflies are more likely to spend their time basking.

Though they didn’t find evidence that the common buckeye’s sensitivity to color differs with time of year, the team did confirm seasonal patterns in the expression of many other genes important for vision and eye development. This indicates common buckeyes may see their environment differently, depending on what time of year they develop as caterpillars.

The next step will be to determine what part of the developmental environment is causing these changes in the visual system (butterflies only live 8-10 days as adults, so they only experience one season). Is it a change in temperature, a change in their visual environment or some other sensory cue?

Observational studies investigating behavior and underlying gene expression in wild populations of animals are uncommon, since natural settings can introduce variance that makes it hard to discern significant patterns. This study reports strong patterns of seasonal response, even outside the controlled conditions of a lab.

Grace Hirzel was first author on the paper published in Functional Ecology. She conducted most of the field work as a Ph.D. student in biological sciences at the U of A while working with Erica Westerman, an associate professor of biological sciences who is the corresponding author on the paper. 

“Working with wild populations allowed us to examine how animals are responding to time of year as whole and under natural settings,” Hirzel explained. “Not only are common buckeye butterflies interacting with their world differently depending on the time of year, but they probably see the world differently at these times of year too. Buckeye butterflies are just one of the many species with obvious seasonal traits. Changes in sensory system development like we found in the buckeye may be a common strategy used by many animals to survive shifting seasonal conditions.” 

Westerman specializes in studying the visual systems of butterflies. Why butterflies? She says she’s interested in the big picture question: do our sensory systems change with our environment and how plastic is our sensory system?

“A great place to start is with a species that you know exhibits plasticity in other areas,” Westerman said. “So, we knew they had plasticity in their wing pattern. If we’re going to get plasticity out in nature in a sensory system, buckeye butterflies are a good species to use...So this is us getting our foot in the door and really trying to answer that big question of ‘how does the development environment influence our sensory perception?’”

Westerman also noted that “one of the reasons we work with this butterfly is that while it’s found throughout the country, it's in really high abundance here in Arkansas. It’s been used for developmental research and understanding how butterflies work for decades. But those populations have always been from the coast where it’s just not quite as common. It meant a lot to me and Grace to work with a local population here. It's a common Arkansas butterfly and it’s really pretty, and I think it's important that some of the species that are common here in Arkansas and the central plains also get showcased in the greater scientific community.”

Co-authors on the paper from the U of A also included Keity J. Farfán-Pira, a postdoctoral fellow in biological sciences, and Chance Powell, a Ph.D. candidate in the same department. Contributors from Cornell included Noah K. Brady, a Ph.D. candidate at the time, and Robert D. Reed, a professor of ecology and evolutionary biology.

Journal

Functional Ecology

DOI

10.1111/1365-2435.70215

Method of Research

Observational study

Subject of Research

Animals

Article Title

Synchronous seasonal plasticity in coloration, behaviour and visual gene expression in a wild butterfly population

Wednesday, December 03, 2025

The ship-timber beetle's fungal partner: more than just a food source

How a symbiotic fungus helps a beetle survive in dead wood

Max Planck Institute for Chemical Ecology

image:
Maximilian Lehenberger with a culture of the ambrosia fungus *Alloascoidea hylecoeti* on an artificial medium.
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Credit: Angela Overmeyer, Max Planck Institute for Chemical Ecology

The ship-timber beetle (Elateroides dermestoides) is a species of ambrosia beetle. Unlike many of its relatives, which are social insects that live in colonies, it is solitary and does not live with other members of its species. While ambrosia beetles usually have generation times of less than a year, the next generation of ship-timber beetles does not hatch for up to two years. It is also one of the largest European ambrosia beetles, reaching lengths of up to 18 millimetres. Despite its solitary lifestyle, the ship-timber beetle does not live alone; it lives in a symbiotic relationship with the ambrosia fungus Alloascoidea hylecoeti, which provides it with nutrients.

First evidence of nutrient symbiosis with the ambrosia fungus

A team led by Maximilian Lehenberger from the Max Planck Institute for Chemical Ecology in Jena investigated this beetle-fungus symbiosis in more detail. To achieve this, the researchers first analyzed the nutrients accumulated by the fungus in its mycelium — the network of thread-like structures that make up its vegetative body. 'Until now, it was only assumed that ambrosia fungi were nutrient-rich. However, there was hardly any useful data to support this. In our study, we were able to demonstrate for the first time that Alloascoidea hylecoeti, in particular, is extremely nutrient-rich. This fungus accumulates many nutrients — significantly more than other fungi, both symbiotic and non-symbiotic — including sugars, amino acids, ergosterol, fatty acids, and the essential elements phosphorus and nitrogen,' says Maximilian Lehenberger, head of the Forest Pathogen Chemical Ecology (FoPaC) project group in the Department of Biochemistry. This probably also explains why the ship-timber beetle can live in nutrient-poor wood for so long and grow so large.

Surviving in a highly competitive environment

The larvae of the ship-timber beetle spend a relatively long time living in the wood of recently deceased trees. This environment is challenging for the offspring of the beetles, which can grow up to two centimeters long, because dead wood is very poor in nutrients and teeming with competition. In social ambrosia beetle systems, individuals can support each other by keeping harmful fungi at bay. This is not the case with solitary beetles. The research team therefore hypothesized that the symbiotic fungus has developed its own strategies to protect itself from competing species. They found that the fungal symbiont Alloascoidea hylecoeti uses various phenolic substances obtained from the surrounding wood. The fungus accumulates these substances to such an extent in its environment that it inhibits the growth of many other fungi. It uses its ability to grow into wood to access further resources. “Unlike many other fungi, the symbiotic fungus is neither broken down nor inhibited by plant defense compounds. Furthermore, it produces many substances that inhibit other fungi,” explains Maximilian Lehenberger.

A fungus that lowers the pH and grows even better in overly acidic environments

The scientists were particularly surprised by the production of acetic acid, which they detected in fungal cultures and samples from beetle nests using nuclear magnetic resonance (NMR) analysis. Experiments with fungal cultures revealed that the ambrosia fungus outcompetes other fungi by 'acidifying' its environment and lowering the pH to as low as 3.5. Remarkably, Alloascoidea hylecoeti not only copes with a very high concentration of acetic acid, but actually thrives at a pH level that is extremely low for fungi. "To date, acetic acid has not been detected in any other ambrosia beetle system. Since we were also able to identify acetic acid in the nests, this is clear evidence that it must play a role in nature too. The fungus utilizes not only acetic acid, but also a variety of other substances to inhibit competing fungi. These include monoterpenes such as linalool, terpineol and citronellol,' says Jonathan Gershenzon, Head of the Department of Biochemistry. Citronellol is responsible for the lemon-like smell of this fungus.

The impact of a highly acidic habitat on the larvae of the ship-timber beetle is unclear, as is the effect of the defensive substances that accumulate in the fungal biomass of their food source. Could this make them less attractive to predators? Could symbiotic bacteria in the beetles' guts help break down high concentrations of phenolic compounds? The research team plans to address these questions and others in future experiments.

Maximilian Lehenberger and Jonathan Gershenzon performing mass spectrometric analysis of substances.