Biology of the Alpine Accentor (Prunella collaris) XI. Inter-individual transfer of information about the wintering site. 16-year study

Abstract

This study represents a 16-year effort to learn about the transfer of overwintering habitat information in Alpine Accentors, encompassing at least three generational replacements. The effects of individual age, position in the flock hierarchy, and presence at local wintering sites were consistently examined. Banding with a combination of colored rings made it possible to identify birds individually over many years. Banded birds were given specific names to better differentiate their behaviour. The study is supported by many minute records of the maintenance activities of individual animals. Of the 27 birds accurately identified between 1987 and 2022, only four were important for the transmission of wintering location information among birds. The birds first arrived there as yearlings, gradually adapted to the environment as residents, and became α-dominant individuals in the wintering flocks. Yearlings usually show little caution when feeding on the site, while young adults, two to three years old, appear to be the most cautious. Six- and seven-year-old adults exhibit less cautious behavior, likely related to their experience. If these birds occupy dominant positions in the hierarchy of a wintering flock, they can feed quickly on familiar food sources and consequently spend considerably more time resting, drilling and preening in safe places. Subordinate birds spend more time trying to feed, which increases their risk of predation. The research provides important insights into how wintering grounds for birds disappear after a ski resort undergoes complete reconstruction. Maintaining wintering grounds requires not only suitable food sources, but also habitual conditions for rest, sunbathing, protection, and temperature regulation. In November and December, two groups arrived that behaved differently and only formed a more cohesive structure as winter progressed in January and February. The distance they kept from humans decreased from November and December to March in the spring. They arrive at their wintering grounds in November, well-fed, with adults weighing over 40 g. Size and weight do not necessarily determine alpha position in the flock (e.g., No. 25). Moreover, hierarchy among adults in winter flocks can change from a year to year. The history of some individuals, such as No. 119, shows that even though they were older and smaller, they had an alpha position in the flock. This suggests that dominance may be based not only on size, but also on experience. Research shows that not all of the flock remains at the wintering site. Some used the location as a temporary stopover in November during migration (No. 9 or 11), while others used it as a stopover in March on their return from other wintering grounds (No. 6), and some only occasionally stayed at the site, for example, in December (No. 24). Some individuals stayed at the site permanently (residents) but remained on the surrounding rocks and did not fly down to search for food from people (No. 4). These individuals flew away with the others from the site to their roosts in the evening. Information transmission obviously requires experienced resident individuals who return to the site for several years. From them, new individuals learn to know not only the location of the site but also the local conditions, and where and how to forage. It is the resident bird that shows several incoming birds the site over several years. Some of them get used to the site in the process of learning this information. In the following years, these newer individuals become residents and play a key role in transmitting information about the wintering site to subsequent generations. Research shows that it is important for the long-term existence of the wintering site and for information transmission, that adults arrive with young yearlings. Some of these yearlings become residents of the wintering site, transmitting information to different generations each year. Some young birds may stay in their wintering grounds for 5–6 years after settling in, while other young birds that appear there in their first year never return. Some individuals observed alone at various wintering sites may play a vital role in helping other birds remember information about those sites in subsequent years (e.g., individual No. 119 in 1993/1994). To realistically study the impact of size or age on the evolution of differential migration, we must cover all age groups of birds in a flock. In the case of Alpine Accentors, it is incorrect to conduct a study for only three or four years and categorize individuals based on their external appearance as yearlings or older adults. This leads to misleading results that do not reflect actual natural processes. This study is exceptional because the age of most individuals was known, allowing us to compare the behavior of several age categories.