Behavioural and energetic consequences of competition among three overwintering swan(Cygnus spp.)species

Background:Winter numbers of the northwest European population of Bewick's Swans(Cygnus columbianus bewickii)declined recently by c.40%.During the same period,numbers of two sympatric and ecologically-similar congeners,the Mute Swan(Cygnus olor)and Whooper Swan(Cygnus cygnus)showed increases or stability.It has been suggested that these opposing population trends could have a causal relationship,as Mute and Whooper Swans are larger and competitively dominant to Bewick's Swans in foraging situations.If so,effects of competition of Mute and Whooper Swans on Bewick's Swans should be detectable as measurable impacts on behaviour and energetics.Methods:Here,we studied the diurnal behaviour and energetics of 1083 focal adults and first-winter juveniles("cygnets")of the three swan species on their winter grounds in eastern England.We analysed video recordings to derive time-activity budgets and these,together with estimates of energy gain and expenditure,were analysed to determine whether individual Bewick's Swans altered the time spent on key behaviours when sharing feeding habitat with other swan species,and any consequences for their energy expenditure and net energy gain.Results:All three swan species spent a small proportion of their total time(0.011)on aggressive interactions,and these were predominantly intraspecific(≥0.714).Mixed-effects models indicated that sharing feeding habitat with higher densities of Mute and Whooper Swans increased the likelihood of engaging in aggression for cygnet Bewick's Swans,but not for adults.Higher levels of interspecific competition decreased the time spent by Bewick's Swan cygnets on foraging,whilst adults showed the opposite pattern.When among low densities of conspecifics(<c.200 individuals/km^(2)),individual Bewick's Swans spent more time on vigilance in the presence of higher densities of Mute and Whooper Swans,whilst individuals within higher density Bewick's Swan flocks showed the opposite pattern.Crucially,we found no evidence that greater numbers of interspecific competitors affected the net energy gain of either adult or cygnet Bewick's Swans.Conclusions:We found no evidence that Bewick's Swan net energy gain was affected by sharing agricultural feeding habitat with larger congeners during winter.This was despite some impacts on the aggression,foraging and vigilance behaviours of Bewick's Swans,especially among cygnets.It is unlikely therefore that competition between Bewick's Swans and either Mute or Whooper Swans at arable sites in winter has contributed to the observed decline in Bewick's Swan numbers.Further research is needed,however,to test for competition in other parts of the flyway,including migratory stopover sites and breeding areas.

Time budget and activity rhythm of wild Great Bustard in winter

Instantaneous scanning and focal animal sampling methods were used to record the behaviors of nine wild Great Bustards(Otis tarda)and their time budget from November 2004 to January 2005.The results indicated that foraging and resting time accounted for as high as 46.40%and 39.12%,respectively,while the rest of the behaviors,such as walking,alerting,preening and flying,only shared 6.83%,2.03%,2.64%and 1.84%,respectively.There were significant differences in foraging time,alert time and walking time between males and females(P<0.05).The preening and flying were closely related to males(Pearson’s correlation,r=0.932),and it was similar for resting and walking in females(Pearson’s correlation,r=0.716).Resting occurred mainly at dawn and dusk,and foraging appeared mostly from 9:30 to 11:30 and from 14:30 to 16:30.Non-parameter testing demonstrates that time budget among resting,flying and others in two temperature intervals(>−5 and℃≤−5)℃was significantly different.

Winter pairs of ruddy shelducks at Lashihai Lake,southwest China

It has been suggested that pairing behavior during winter in migratory ducks represents a trade-off between costs(defense of the female)and benefits(early access to females).To investigate the benefits and costs for both sexes in wintering pairs of ruddy shelducks(Tadorna ferruginea),we compared time budgets for paired males and females,and surveyed the sex ratio of the birds wintering at Lashihai Lake,southwest China.The behavior of the paired ruddy shelducks was monitored for 5 activity types:feeding,resting(including sleeping),preening,drinking and warning.Feeding was the most dominant activity.The feeding time of both sexes increased as the winter season progressed.However,the paired females always spent significantly more time feeding and less time warning than the paired males.Paired ruddy shelducks had access to better feeding grounds than unpaired individuals,resulting in a food benefit for paired individuals over single individuals.Because the sex ratio of the wintering population was strongly male biased(M:F=1.44:1.00),the paired male also gained the benefit of accessing a female in advance of the breeding season.