A 2025 study found that Himalayan monals living in a noisier habitat made calls with higher peak frequencies than birds in a relatively quiet habitat. The study also reported a slight difference in call duration. It shows an association between habitat noise and vocal traits—not proof that noise alone caused a permanent change or that the birds’ breeding or survival is being affected.
What researchers compared
The Himalayan monal (Lophophorus impejanus) is a Himalayan pheasant. In a study published in Behavioural Processes in August 2025, researchers compared its calls in two habitats in Kedarnath Musk Deer Sanctuary, Uttarakhand: Chopta Valley, which receives road traffic and many visitors, and the relatively undisturbed Madmaheshwar Valley. They used passive acoustic monitoring devices and a microphone across seasons, then analyzed call characteristics alongside noise variables using quantile regression. The available reporting says they recorded hundreds of calls but does not give a precise count.
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The comparison asks whether vocal traits differ with the sound environment. It does not isolate noise from every other difference between the two valleys, so the findings are best read as a relationship between habitat conditions and calls, rather than a controlled demonstration that noise alone produced the differences.
What changed in the calls
Peak frequency was higher in the noisier habitat
Calls from the noisier habitat had a higher peak frequency. The study also reported that noise selectively affected upper-frequency components. Its quantile-regression results indicate a stronger model fit at higher points in the vocal-frequency distribution: pseudo-R² was 0.231 at the 10th quantile, 0.215 at the 50th, 0.454 at the 75th and 0.734 at the 95th. These are model statistics for different quantiles—not percentages of birds or calls that changed.
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The study’s reported mean absolute error rose from 142.14 at the 10th quantile to 185.49 at the 95th. Those values describe model error; they do not measure how much a bird raised its voice. The indexed abstract does not provide units for these figures.
Call duration differed only slightly
The study also found longer calls in the noisy habitat, but its abstract characterizes the difference in call length as slight. The frequency result is the clearer reported shift; the duration finding should not be inflated into a claim of a large or uniform change.
Why human activity may matter
Traffic, visitors and other human activity can raise background sound levels. Co-author Anand Kumar told The Indian Express that the noise came “either through transportation or the heavy footfall from the pilgrimage.” A change in the frequency or duration of a call could affect how it stands out against background sound, but the study does not establish that this is why individual birds call differently.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Calls matter in the species’ mating behavior: co-author Rajeev Lochan told the newspaper, “The male makes the mating call and the female responds to that call.” But the reported findings do not show whether the observed vocal differences alter female responses or mating success.
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What the study does—and does not—show
- It shows: calls recorded in two habitats with different levels of human activity and ambient noise differed in peak frequency, with a slight reported difference in duration.
- It does not establish: that noise alone caused the differences, that the change is permanent or evolutionary, or that mating, breeding behavior or long-term survival has been affected.
- It cannot settle local population health: The Indian Express describes the monal as globally Least Concern on the IUCN Red List, while also reporting that reliable local population data are lacking. A global category is not proof that every local population is secure.
The researchers are reported as calling for noise management in heavily visited areas. That is not a call to end tourism; it is a reason to consider how traffic and visitor noise can be managed where wildlife lives.
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Sources and study details
- Behavioural Processes study record: “Noise-induced vocal shifts in the Himalayan Monal (Lophophorus impejanus) vocal distribution in two different habitats,” volume 230, August 2025, article 105236, DOI 10.1016/j.beproc.2025.105236.
- PubMed abstract (PMID 40639750), including the reported quantile-regression findings.
- The Indian Express report, September 19, 2026, for the locations, researchers’ comments, limitations and conservation context.
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