Predicting avian herbivore responses to changing food availability and competition

Wood, Kevin A.; Stillman, Richard A.; Newth, Julia L.; Nuijten, Rascha J.M.; Hilton, Geoff M.; Nolet, Bart A.; Rees, Eileen C.

doi:10.1016/j.ecolmodel.2020.109421

Cited by 6 publications

(3 citation statements)

References 61 publications

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“…Despite some evidence that Bewick's Swans altered their patterns of behaviour when sharing feeding habitat with interspecific competitors, their overall rates of net energy gain at the study site were not affected. Our results suggest that swans have at least some capacity to adjust the relative amounts of time devoted to key behaviours in order to maintain consistent levels of energy gain, as predicted by Wood et al (2021). The mean estimates of net energy gain derived indicated that all species and age classes could achieve positive energy gains during winter.…”

Section: Discussionsupporting

confidence: 54%

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

et al. 2021

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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/km2), 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.

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Section: Discussionsupporting

confidence: 54%

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

et al. 2021

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“…Our GPS tracking study implies that the Bewick's swan is adapting to climate change in the non‐breeding season in terms of winter range selection on the individual level. Yet, it is a topic for future study whether the potential for the species to further shift their winter range might be limited by, for example, food availability (Wood, Stillman, et al, 2021), competition (Wood, Newth, et al, 2021), hunting pressure (Newth et al, 2011) or changes therein in the newly suitable parts of the winter range. Furthermore, it is unknown if there are carry‐over effects of migration distance on for example timing of arrival on the breeding grounds, breeding propensity and ultimately breeding success.…”

Section: Discussionmentioning

confidence: 99%

Migratory swans individually adjust their autumn migration and winter range to a warming climate

Linssen,

van Loon,

Shamoun‐Baranes

et al. 2023

Global Change Biology

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In response to climate warming, migratory animals can alter their migration so that different events in the annual cycle are better aligned in space and time with suitable environmental conditions. Although such responses have been studied extensively during spring migration and the breeding season, much less is known about the influence of temperature on movements throughout autumn migration and how those movements result in a winter range and shifts therein. We use multi‐year GPS tracking data to quantify how daily autumn movement and annual winter distance from the breeding grounds are related to temperature in the Western Palearctic Bewick's swan, a long‐lived migratory waterbird whose winter range has shifted more than 350 km closer to the breeding grounds since 1970 due to individuals increasingly ‘short‐stopping’ their autumn migration. We show that the migratory movement of swans is driven by lower temperatures throughout the autumn season, with individuals during late autumn moving only substantially when temperatures drop below freezing. As a result, there is large flexibility in their annual winter distance as a response to winter temperature. On average, individuals overwinter 118 km closer to the breeding grounds per 1°C increase in mean December–January temperature. Given the observed temperature increase in the Bewick's swan winter range during the last decades, our results imply that the observed range shift is for a substantial part driven by individual responses to a warming climate. We thus present an example of individual flexibility towards climatic conditions driving the range shift of a migratory species. Our study adds to the understanding of the processes that shape autumn migration decisions, winter ranges and shifts therein, which is crucial to be able to predict how climate change may impact these processes in the future.

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“…However, during the coldest and longest winter nights in northern Europe, Great Tits (Parus major) lose up to a quarter of their evening body mass, which needs to be replenished the next day [5,6]. While energy reserves are essential to avoid starvation, wintering birds usually maintain their body reserves below their physiological capacity, suggesting costs associated with excessive body energy reserves [7,8]. It has been suggested that predation risk represents a cost of being fat because higher body mass may make birds escaping prey slower to take flight and to escape [9].…”

Section: Introductionmentioning

confidence: 99%

Permanent Ad-lib Feeders Decrease the Survival of Wintering Great Tits (Parus major)

Krama

Popovs

Trakimas

et al. 2023

Birds

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The optimal body mass hypothesis posits that the body reserves of wintering birds are balanced between the risk of starvation and predation. In this study, we tested whether the body mass of wintering Great Tits (Parus major) was higher under conditions of less predictable food resources. We compared body mass, body mass index, the speed at take-off, and apparent survival of Great Tit adult males wintering in small urban areas either near feeders providing permanent access to food for months or near feeders providing irregular access to food. Body mass and body mass index were greater, while take-off speed and apparent survival were lower, in birds wintering near permanent feeders than birds wintering near irregular feeders. Thus, urban birds, with their predictable access to high energy food, did not follow the fattening strategy predicted by the optimal body mass hypothesis. This study shows that regular excess amounts of high-energy food may affect urban birds’ physiological and behavioral strategies in a non-adaptive way. We recommend irregular feeding of wintering birds and the placing of feeders in places that are safe against attacking predators.

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Predicting avian herbivore responses to changing food availability and competition

Cited by 6 publications

References 61 publications

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

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

Migratory swans individually adjust their autumn migration and winter range to a warming climate

Permanent Ad-lib Feeders Decrease the Survival of Wintering Great Tits (Parus major)

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