Using live-streaming webcams to assess behavioural responses of waterbirds to changes in swan density

Using a live-streaming webcam to assess the behavioural responses of waterbirds to changes in the density of swans Cygnus spp.

By Kevin A. Wood¹, Grace Clarke², and Paul E. Rose¹,²

¹Wildfowl & Wetlands Trust (WWT), United Kingdom.

²University of Exeter, United Kingdom

Swans exhibit aggression towards other swans and smaller waterbirds, including threat displays and strikes made using the bill, wings and body. Such aggression allows swans to acquire and retain access to key resources, such as food or breeding territories, and occurs throughout the annual cycle (Tingay et al., 1974; Wood et al., 2020).

Although this aggression is well documented, the consequence for other birds has received relatively little attention from researchers. Understanding the interactions between swans and other waterbirds has become more urgent, as among many swan populations globally, numbers of swans have risen in recent decades (Rees et al., 2019).

A pair of Mute swans (Cygnus olor). Photo by WWT.

Peoples’ perceptions of the impacts of swans on other waterbirds influence waterbird management and conservation activities. As an example, local concern regarding the impact of swans on other waterbirds has been identified as a motivation for the illegal persecution of the legally protected Bewick’s Swan Cygnus columbianus bewickii in the northwest Russian Arctic (Newth et al., 2022). Yet, without information on behavioural interactions between swans and other waterbirds, it is unclear whether swans have impacts on smaller waterbirds. Moreover, it is not known whether any such impacts are density dependent, such that rising swan densities might increase any impacts. Assessments of the impacts of swans on other waterbirds are therefore needed to help to inform the management of waterbird populations.

In our new study, published open access in Wildlife Biology (Wood et al., In press), we used a live-streaming webcam at WWT Caerlaverock (northwest UK) to address whether the behaviour of different waterbird taxa varied in response to different densities of swans. WWT Caerlaverock is an important wintering site for Mute Swans (Cygnus olor) and Whooper Swans (Cygnus cygnus), as well as a range of smaller waterbirds. Our approach allowed us to evaluate the impact that these two swan species might have on the behaviour of overwintering waterbirds. Using the webcam to conduct time-activity budget observations, we obtained a total of 197 focal observations of four waterbird taxa, comprising ducks, geese, rails, and swans.

Whooper Swan (Cygnus cygnus) by Richard Taylor-Jones.

All four of the behaviours that we recorded (aggression, foraging, preening, and resting) varied among waterbird taxonomic groups, as well as with the month and time of day of observation, and prevailing weather conditions. Swan density showed negative relationships with the time spent on aggression and resting, a positive relationship with time spent preening, and no relationship with the time spent on foraging. Whilst these relationships were detected, the changes in the percentage of the total time spent on each behaviour were small. For example, a doubling of swan density from 91 to 182 ind. ha-¹ resulted in a decrease in aggression among ducks from a mean of 2.7 to 2.0%, an increase in preening among geese from 29.1 to 31.7%, and a decrease in resting among ducks from 16.8 to 13.7%. Even at high swan densities (up to a maximum of 182 ind. ha-¹ at our study site), the times spent on aggression, preening, and resting behaviours typically remained within the ranges reported for waterbirds, suggesting that any impacts of swans on waterbird behaviour were quite limited. Crucially, the lack of any relationship between waterbird foraging and swan densities indicates that rising swan densities are unlikely to impact waterbirds efforts to meet their energy and nutrient requirements, at least for the range of swan densities recorded in our study.

Our findings suggest that the impacts of rising swan numbers on the behaviour of waterbirds are likely to be low. However, our study was conducted at only one site during a single winter, and so further studies are needed to assess swan impacts on a broader range of waterbirds, at a greater range of sites, and during other parts of the annual cycle (e.g. the breeding season when swans defend breeding territories). Finally, our study highlights how live-streaming webcams can be used to answer emerging questions in wildlife behaviour research.

The full article can be found here: https://doi.org/10.1002/wlb3.01504

References

Newth, J.L., et al. 2022. Predicting intention to hunt protected wildlife: a case study of Bewick’s swan in the European Russian Arctic. Oryx, 56: 228–240.

Rees, E.C. et al. 2019. Conservation status of the world’s swan populations, Cygnus sp. and Coscoroba sp.: a review of current trends and gaps in knowledge. Wildfowl, Special Issue 5: 35–72.

Tingay, A. 1974. Aggression in the black swan. Emu, 74: 35–38.

Wood, K.A., et al. 2020. Aggressive behavioural interactions between swans (Cygnus spp.) and other waterbirds during winter: a webcam-based study. Avian Research, 11: 30.

Wood, K.A., et al. In press. Using a live-streaming webcam to assess the behavioural responses of waterbirds to changes in the density of swans Cygnus spp. Wildlife Biology.