New Year's Eve Fireworks Can Disrupt Bird Behaviour for Days
Every New Year's Eve, fireworks fill the night with intense noise and light for only a few hours, yet their effects on roosting birds may persist far longer. Urban birds routinely encounter vehicles, human activity and a wide range of background noise, but sudden explosive sounds can still represent a very different form of disturbance. One study followed birds along the River Rhine in Basel, Switzerland, over three consecutive winters. The study site contained a long-established winter roost of black-headed gulls (Chroicocephalus ridibundus), with as many as approximately 5,000 birds. The gulls usually rested on the water within the port basin, although they sometimes moved onto the adjacent Rhine. The area itself was far from quiet: nightlife venues were located nearby, port vessels continued operating after dark, and artificial lighting was abundant. These black-headed gulls were therefore already accustomed to considerable levels of human disturbance.
Observations were conducted over three winters, from 2020/2021 to 2022/2023. Each year, the night of 27 December served as a control night close to New Year's Eve, and bird activity was then recorded throughout the night from 31 December to 1 January. Observations began after sunset as black-headed gulls arrived at the roost and continued until shortly before sunrise. The researcher also repeatedly counted the number of gulls using the roost from late December into late January to determine how long it took the birds to recover after New Year's Eve.
To quantify the severity of disturbance, the researcher recorded flight time and several disturbance behaviours in 15-minute intervals. These included whether the gulls left their preferred roost within the port, whether the entire flock moved elsewhere, whether the flock occupied a shorter section of the river, whether individuals clustered more tightly together, and whether birds were flushed into flights exceeding 50 m above ground level. Fireworks were classified as either close fireworks, occurring within approximately 100 m of the roost, or distant fireworks that could still be heard from the study area.
On control nights, black-headed gulls spent almost all of their time resting on the water, and flight activity remained very low. On New Year's Eve, however, the proportion of time spent flying increased sharply, particularly around midnight. Statistical analyses also showed that more frequent close fireworks were associated with longer flight times. Around midnight, entire flocks were observed remaining airborne for as long as approximately 45 minutes, while the mean accumulated flight time of some black-headed gulls reached as much as about 2 hours over the course of the night.
Once fireworks began, the gulls also left their preferred roosting sites, occupied a smaller section of the river, clustered more tightly together and, in some cases, abandoned their usual roosting area entirely. The researcher combined these behaviours into a disturbance score. Unlike flight time, the disturbance score was not significantly associated with the number of fireworks occurring at a particular moment. One possible explanation is that these behavioural responses were cumulative. Repeated explosions had already altered the birds' roosting locations and flocking behaviour, and they did not immediately return to normal even during temporary periods without fireworks.
The effects extended beyond New Year's Eve itself. Comparing gull numbers at the roost on 27 December with those on 1 January, abundance declined by approximately 17.1%, 37% and 62.4% across the three winters, respectively. Some birds may simply have moved to other roosts, so these figures represent declines at the original study roost rather than mortality. The gulls gradually returned, but disturbance-related behaviours persisted for some time. In 2020/2021, abnormal behaviour continued until at least 1 January; in 2021/2022, it persisted until 5 January; and in 2022/2023, altered behaviour within the port area was still recorded on 6 January. Firework use was lowest during the winter of 2020/2021 because of COVID-19-related restrictions, and that winter also showed the weakest flight and disturbance responses and the fastest recovery.
Other waterbirds reacted even more rapidly than the black-headed gulls. Mallards (Anas platyrhynchos), mute swans (Cygnus olor) and Eurasian coots (Fulica atra) were present throughout the control nights, but their numbers on the water fell quickly after the first close fireworks on New Year's Eve. By midnight at the latest, no other waterbirds were observed within the study area, and more than 90% remained absent until at least early morning. Most returned during the daytime on 1 January. During the winter of 2021/2022, the researcher searched approximately 6 km both upstream and downstream along the Rhine and found that areas normally occupied by several species of wintering waterbirds were almost completely empty. Only some mute swans remained, having moved into the most sheltered sections of the river. Local passerines were also affected by the fireworks.
For several days after New Year's Eve, black-headed gulls were more frequently observed resting during the day, sitting with their eyes closed or with their heads tucked into their feathers. Foraging birds were also more easily flushed by people or sudden noises, were less likely to approach humans for food, and changed their usual daytime roosting locations. These observations were based primarily on field behaviour; the study did not measure stress hormones or other physiological indicators.
Restricting fireworks near major bird roosts and shortening the duration of concentrated firework activity may therefore help reduce these disturbances. The study also suggests that shorter periods of disturbance are associated with faster behavioural recovery in the affected birds.
Author: Shui-Ye You
Reference:
Moser V. (2026). Birds on fire: severe disturbance by fireworks in wintering gulls, waterbirds and passerines. Animal Behaviour.
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