Aggressive behavioural interactions between swans (Cygnus spp.) and other waterbirds during winter: a webcam-based study

• Published in: Avian Research
• Main Authors: Kevin A. Wood, Phoebe Ham, Jake Scales, Eleanor Wyeth, Paul E. Rose
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2020
• Subjects: Aggression; Agonistic behaviour; Bewick’s Swans; Intraspecific versus interspecific competition; Remote data collection; Waterfowl; Zoology; QL1-991; Cygnus cygnus; Whooper Swan
• Online Access: https://doi.org/10.1186/s40657-020-00216-7; https://doaj.org/article/206178eac3a24a09b3cabec99e2cd10d

Abstract Background Our understanding of any impacts of swans on other waterbirds (including other swans), and potential effects on waterbird community structure, remain limited by a paucity of fundamental behavioural and ecological data, including which species swans interact aggressively with and how frequently such interactions occur. Methods Behavioural observations of aggression by swans and other waterbirds in winters 2018/2019 and 2019/2020, were carried out via live-streaming webcams at two wintering sites in the UK. All occurrence sampling was used to identify all aggressive interactions between conspecific or heterospecifics individuals, whilst focal observations were used to record the total time spent by swans on aggressive interactions with other swans. Binomial tests were then used to assess whether the proportion of intraspecific aggressive interactions of each species differed from 0.5 (which would indicate equal numbers of intraspecific and interspecific interactions). Zero-inflated generalized linear mixed effects models (ZIGLMMs) were used to assess between-individual variation in the total time spent by swans on aggressive interactions with other swans. Results All three swan species were most frequently aggressive towards, and received most aggression from, their conspecifics. Our 10-min focal observations showed that Whooper (Cygnus cygnus) and Bewick’s Swans (C. columbianus bewickii) spent 13.8 ± 4.7 s (means ± 95% CI) and 1.4 ± 0.3 s, respectively, on aggression with other swans. These durations were equivalent to 2.3% and 0.2% of the Whooper and Bewick’s Swan time-activity budgets, respectively. Model selection indicated that the time spent in aggressive interactions with other swans was best-explained by the number of other swans present for Whooper Swans, and an interactive effect of time of day and winter of observation for Bewick’s Swans. However, the relationship between swan numbers and Whooper Swan aggression times was not strong (R 2 = 19.3%). Conclusions Whilst swans do exhibit ...