In a Malaysian forest squeezed between housing developments and roads, white-handed gibbons are singing less in the mornings compared to those in quieter areas, according to research by Benjamin Galea, a final-year PhD student at Universiti Sains Malaysia. The study, which has not yet been peer-reviewed, involved recording and analyzing the morning calls of these primates in three different locations with varying levels of background noise: a spot near a highway, a popular hiking trail, and a secluded beachfront area far from human activity. The study found that as background noise increased, gibbons were less likely to call. Gibbons living near the highway called in only 36% of the recordings, compared to 71.4% at the beach and 84.6% at the hiking trail. Within each site, the odds of calling also decreased as the noise level increased. The gibbons near the hiking trail sang more frequently than those at the beach, possibly because they were closer to another gibbon group, prompting territorial singing. Additionally, their location in the forest interior meant they faced less noise disturbance. Gibbons near the highway may have avoided singing due to the loud traffic, or they might have started singing earlier than the study's monitoring period, which ran from 6 a.m. to 1 p.m. Some recordings began as gibbons were already in the middle of their songs. Singing earlier could help them avoid the noise, but it might interfere with their rest, foraging, or communication with other groups. When the highway gibbons did sing, most of their vocalizations occurred in solo songs, but it's unclear if this reflects natural differences or the impact of noise on coordination between pairs. This research contributes to a growing body of studies showing how human-generated noise disrupts animal behavior. Noise pollution has been linked to reduced hearing abilities in mammals and various effects on birds, including fewer surviving young and less biodiversity in urban areas. Understanding the exact impact of noise on gibbons requires more study. Ulrich H. Reichard, a professor of anthropology not involved in the study, notes that it's unclear how often gibbons need to call to communicate effectively. Even with constant noise, they might not need to call every day or for long periods to achieve their goals. If gibbons sing less, they may not be at higher risk of predation, as they can move quickly through the trees to escape. However, this could affect other animals like birds and squirrels, which rely on gibbon warnings. Changes in interspecies communication could have broader ecological consequences. The white-handed gibbon is listed as endangered by the IUCN, with its population believed to have declined by more than 50% over the past 45 years due to habitat loss, hunting, and capture for the pet and photo-prop trade. In Malaysia, while there is no recent population estimate, the number of white-handed gibbons is thought to have declined over recent decades. Surprisingly, they continue to live in isolated forest fragments within urban areas, including the capital, Kuala Lumpur. In Malaysia, a forest fragment may appear to be suitable gibbon habitat physically, with trees, food, and sleeping spots, but it could be surrounded by roads, housing, or industrial noise. Nadine Ruppert, an associate professor at Xishuangbanna Tropical Botanical Garden and a supervisor of the research, emphasizes the need to consider habitat quality beyond just the amount of forest remaining. As urban and peri-urban forests gain recognition for their conservation value, it's important to consider the experiences of animals within these spaces.