Wing-feather moult of the White-backed Woodpecker Dendrocopos leucotos lilfordi

Abstract

Determining the age of specimens is of great help in wildlife management, especially for rare or threatened species in which each individual has a high value. In birds, differences in moulting pattern between juveniles and adults may in some cases allow determination of a bird’s age from the examination of its plumage. In the present study, we analyse the moult of 19 breeding individuals of White-backed Woodpecker Dendrocopos leucotos lilfordi captured for GPS tagging in the Pyrenees, in order to describe, for the first time, the moulting pattern of this endangered woodpecker. Two well-differentiated groups of adult birds were identified: those that underwent a partial moult, and were classified as second-calendar-year birds, and those that performed a complete one and were classified as older. The first group had renewed most lesser and median coverts, all primaries and the innermost greater coverts, thus showing clear moult limits between the primaries and secondaries and within the greater coverts. Some individuals also replaced up to two more greater coverts (GC5–6). Individuals classified as older birds showed all feathers to be of a single generation, indicating that they had undergone a complete moult. A few individuals in this category retained a few unmoulted secondaries and primary coverts, however. A recapture of a bird with a complete moult, which had been captured a year before showing a partial moult, would confirm these moult sequences to be age dependent. This moulting pattern is very similar to that described for other spotted woodpeckers, and allows researchers to determine the ages of breeding individuals during the nesting season. ARTICLE HISTORY Received 7 December 2020 Accepted 11 March 2021 Feathers are structures that wear due to the action of external agents, such as weather and ectoparasites (like mites or lice), so must be periodically replaced. This renewal of feathers is called moult and it is, together with breeding and migration, one of the most energydemanding events in a bird’s life cycle (Newton 2009). To prevent the demand for energy becoming unsustainable, moult has little or no overlap with the other two processes in small and medium-sized birds (Jenni &Winkler 2020 a, b). For this reason, moult patterns vary between species, even between populations, depending on their migratory behaviour and reproductive strategy (Ginn & Melville 1983). Furthermore, moult patterns can also vary among individual birds within a population: for example, it is common for adults to undergo different moults from younger birds (Svensson 1992, Baker 1993, Demongin 2013). This difference between age classes is very useful to distinguish age in most birds: hence, plumage examination and the identification of the feathers involved in a given moult process is often useful for ageing. For instance, among small and medium-sized birds like most passerines or woodpeckers, many long-distance migrants have too little time to moult after breeding and before the post-breeding migration, as they normally breed relatively late within the season and depart early to their wintering grounds (Newton 2009). Therefore, in these species, first-year birds and adults usually moult all their plumage after they reach their wintering areas (Jenni & Winkler 2020a). In autumn, these two age categories can be distinguished because the adults will have heavily worn plumage, while the first-year birds will show new, fresh plumage (e.g. Svensson 1992). Resident species, however, normally have a long period after breeding and before the harshest part of the winter and, therefore, both first-year birds and adults can undergo a complete moult after breeding (Jenni & Winkler 2020a). In © 2021 British Trust for Ornithology CONTACT Diego Villanúa diegovillanua@yahoo.es RINGING & MIGRATION 2020, VOL. 35, NO. 1, 1–5 https://doi.org/10.1080/03078698.2021.1974526 these cases, once this moult has ended there are no differences between these two age groups. Between these two strategies, there are intermediate moult patterns that are often characterised by complete moults in adults, and partial ones in first-year birds (Svensson 1992). In the largest species, like many eagles and vultures and some owls, feathers cannot all be replaced in a single year, giving rise to more complex moult patterns that, overall, often allow several age classes to be differentiated (Baker 1993, Demongin 2013, Zuberogoitia et al 2015). Despite the importance of moult for birds, due to its pivotal role within the annual cycle of every bird, studies dealing with this subject are not common and they are often based on the analysis of museum skins rather than on birds captured alive (Newton 2009). This scenario applies particularly to the European woodpeckers (but see Baker 1993, Winkler et al 1995, Demongin 2013, Winkler 2013, Blasco-Zumeta 2020). In general, adult woodpeckers would undergo a complete moult just after breeding, while juveniles would do a partial moult that would affect the tail, primaries, body feathers, lesser and median coverts and some (inner) greater coverts (Baker 1993, Winkler et al 1995, Pyle & Howell 1996, Demongin 2013, Winkler 2013, Blasco-Zumeta 2020). By contrast, all or most primaries, secondaries, tertials and (outer) greater coverts would be retained, so that in these cases the juvenile feathers would remain until the first complete moult in the second year of life. A detailed description of moult has not yet been compiled for the Pyrenean population of the Whitebacked Woodpecker Dendrocopos leucotos lilfordi (Cramp 1985). The only information about this issue comes from a study probably based on four museum skins, where it is simply mentioned that adults may renew most of their plumage by October (Purroy 1972). According to Cramp (1985), the White-backed Woodpecker moults like the Great Spotted Woodpecker Dendrocopos major but with earlier timing. Nothing is reported about differences between populations, though the paucity of data on lilfordi is acknowledged (Cramp 1985), This well-differentiated taxon could qualify as a separate species, according to recent genetic studies (Pons et al 2020). The development of a project in the Spanish Pyrenees aiming to tag some White-backed Woodpeckers with GPS devices has also allowed us to document moult. Thus the aim of the present study is to describe the moult of breeding individuals of White-backed Woodpecker, to evaluate how moult may vary between age classes and assess how an examination of the extent of moult might be useful for ageing. Material and methods The fieldwork was carried out in three forests of beech Fagus sylvatica in the Navarran Pyrenees, all of them designated as Natura 2000 sites (codes ES0000126, ES2200019 and ES2200018). Overall, these sites host more than 90% of the White-backed Woodpeckers in Spain (Campión & Senosiain 2004). Birds were captured for a GPS-tagging programme that started in 2017 (HABIOS project; Campión et al 2020a, b). Captures were made during the breeding period using mist nets placed close to nests, at heights of 9.25– 12.95 m, using a pulley system (Campión et al 2020b). Once captured, every bird was ringed, aged as juvenile or older bird (juvenile birds were those showing juvenile plumage, before moulting any feather), measured and equipped with a GPS (Campión et al 2020b). Then, photographs of one of the wings (dorsal view), the rump and the tail were taken in order to examine their moult status. Finally, the state of moult was recorded according to Ginn & Melville (1983) assigning the value 0 to the old feathers, 5 to the new feathers and 1–4 to the growing ones. In the cases in which, for various reasons, the moult record could not be made at that time, this information was obtained from the photographs.