Flocking of Foraging Yellow-Billed Choughs Pyrrhocorax Graculus Reflects the Availability of Grasshoppers and the Extent of Human Influence in High Elevation Ecosystems

Abstract

Mountain ecosystems are subject to many pressures, including changes in land use, rising temperatures and increasing recreational activities. These factors may disrupt food webs, threatening the survival of organisms and, ultimately, ecosystem functioning. However, few studies focus on the trends of different groups joined by trophic links in alpine ecosystems. The Yellow-billed (Alpine) Chough, Pyrrhocorax graculus, a gregarious bird that moves in flocks, is an ideal target species within this framework since it has a grasshopper-based diet during the summer and may inhabit sites that are heavily developed for recreational activities. We tested therefore whether flock size co-varied with grasshopper abundance along an elevational gradient in two alpine areas subject to different levels of human disturbance. Chough flock size and grasshopper abundance were measured along elevational transects. The median flock size was analysed in relation to grasshopper abundance and biomass, also performing negative binomial GLMs account for effects of period (i.e. from June to mid-August), site and elevation. In both study areas, chough flocks were larger at the elevation where grasshoppers were more abundant. This may indicate the capacity of the species to follow large scale fluctuations in their key insect prey. On the other hand, the relationship between flock size and grasshopper biomass was positive at a natural site and negative at a tourist site. This suggests that where there is a high level of human pressure, other factors, such as the availability of human-provided food, may disturb the natural relationship between choughs and their key prey. Overall, our results indicate that flocking by foraging Yellow-billed Choughs reflects both grasshopper abundance and the degree of anthropogenic influence. Messerli 2001;Brambilla et al. 2016).The study of high elevation food webs in this transforming environment is particularly urgent because any change in trophic interactions between organisms may affect organism survival and, ultimately, ecosystem functioning. Climate change, for instance, can affect trophic relations through the phenological mismatch that reduce the food supply for breeding birds (Flousek et al. 2015;Thackeray et al. 2016). However, studies on food web components and/or on trends in different groups joined by trophic links are scarce. Indeed, studies focussing on the distribution and trends of alpine species (Chamberlain et al. 2012), and relationships between predators and prey in humanimpacted high elevation areas, have been severely neglected so far (Vallino et al. 2019). The Yellow-billed (Alpine) Chough, Pyrrhocorax graculus, a gregarious bird that moves in flocks throughout the year, is an excellent target species in this context. It is generally assumed that flocking may be advantageous to detect predators (Rolando et al. 2001;Jiménez et al. 2013), and has additional survival value in relation to food finding (Ward and Zahavi 1973), for instance through sharing information about food localisation (F...

The foraging ecology of yellow-billed and red- billed choughs changed between two climatically different years

“…Insects constitute the main prey of both corvid species during the summer months 35 . The presence of epigeal insects can be assessed indirectly by passing a stick through the grass and counting the insects that are flushed out 24 , 26 , 33 . Vice-versa, to our knowledge, there is no practical method for assessing the presence of underground insects.…”

“…The yellow-billed chough is widespread in the European Alps (it is also known as the Alpine chough), where it has been extensively studied since the 1990s. Research on these breeds has focused on their breeding biology 23 , foraging behaviours 24 – 26 , local movements 27 – 29 , survival 30 and relationships with man 31 – 34 . In the western Italian Alps, the two species are sympatric and may also be present in the same habitat at the same time (syntopy).…”