Predicting avian herbivore responses to changing food availability and competition

Many species of large herbivore rely on agricultural land for their feeding habitats, but available food resources are highly variable in space and time. The conservation management farmland-dependant herbivores would therefore benefit from predictions about how will respond to changes environment. We developed an individual-based model (IBM) provide such three overwintering avian that feed land: Bewick's swans (Cygnus columbianus bewickii), whooper cygnus), mute olor). Our validated predicted potential future availability competition affect (i) the proportion current swan population could be supported, (ii) successfully departed migration at end winter, (iii) daily foraging effort, (iv) late winter crop biomasses. Regardless competitor numbers or availability, all individuals were avoid starvation depart successfully. Individual offset higher reduced by increasing daylight spent foraging. simulations indicate have considerable capacity buffer against losses increased this may result additional grazing damage crops. findings suggest recent c.40% decline was unlikely linked competition.