Application of a global age-coding system (“WRP”), based on molts and plumages, for use in demographic and other studies of birds

Abstract

Determination of a bird’s age or cohort is critical for studies on avian demography, occurrence patterns, behavior, and conservation management. Age designations have largely been developed in north-temperate regions and utilize calendar-based or seasonally based codes; however, in tropical regions and in the southern hemisphere, these coding systems have limited utility at best. To address these issues, we had previously devised the “WRP system,” based on the nomenclature of Humphrey and Parkes (H–P) and Howell et al., which defines molts in an evolutionary context applicable to birds globally. Here we refine and build upon core concepts and definitions of the WRP coding system, resolving key limitations that were identified during its first decade of use. The WRP system employs a three-letter alpha code in which each letter describes a different aspect of H–P terminology: the molt cycle (which informs a bird’s age) and molt and plumage status within the cycle (each of which can also inform age). Here we recommend the continued use of most of the original (“core”) WRP coding while augmenting the system with an optional adjunct-code entry for comprehensiveness, clarity, and flexibility, and we clarify a few additional codes to cover less common molting and plumage strategies. For most users, from 7 to 13 core and 1 adjunct WRP code will be sufficient to describe all plumages and provide molt status and ages for demographic studies or other purposes. The revised WRP system is flexible enough to be adapted to the specific goals of programs while also providing core codes that can facilitate the comparison of avian age, molt, and plumage status on a global basis. We anticipate that our revised and standardized version of the WRP system will be easily adopted and could eventually replace calendar-based and seasonally based coding.

Habitat use of Amazonian birds varies by age and foraging guild along a disturbance gradient

“…Specifically, many species go through a partial to incomplete preformative moult ( sensu [52]) resulting in discernable moult limits, thereby facilitating the identification of juvenile, formative and definitive basic plumaged individuals [51]. Given that the calendar year system of age classification ( de facto system used in North America and Europe) is not appropriate for tropical species with less seasonal breeding periods [53], we used a global age-coding system (WRP) based on known sequences of moults and plumages (see [51,54,55] for a full explanation of moult codes used below). Species that have a partial or incomplete preformative moult and were classified as FCJ, FPJ, FCS, FPS and FPF (first moult cycles juvenile or supplemental) are referred to here as ‘young’.…”

Solar Bird Banding: Notes on Changes in Avian Behavior While Mist-netting During an Eclipse

“…We then fitted aluminum butt-end leg bands (Bird Banding Laboratory, USGS) on the legs of newly-captured birds, and recorded the band numbers of recaptured individuals that were first banded on a prior day. We next assessed the age and sex of individuals (Pyle 2022), examined the body and flight feathers for signs of molt, and then determined the WRP code (Pyle 2022; Pyle et al 2022). We then recorded morphometric information such as fat score, body condition (Kittelberger et al 2022), wing length, and body mass, the latter of which we calculated by weighing a bird on a scale.…”

Defining moults in migratory birds: a sequence‐based approach

“…All birds have a well‐defined annual (or nearly annual) moulting episode that involves growth or replacement of all or nearly all feathers, termed the prebasic moult (Humphrey and Parkes 1959; Fig. 1); this moult forms the foundation for H–P terminology (Howell et al 2003, Howell and Pyle 2015, Pyle et al 2022). Moult ‘cycles' are defined as those occurring between prebasic moults, as marked by initiation of a prebasic moult.…”

“…Prealternate and presupplemental moults have emerged at different times along ancestral bird lineages, and are thus not considered homologous throughout all birds (Howell et al 2003, Pyle 2007), just within each linage from the time the moult first evolved. Such an evolutionary approach can be applied to birds globally, rather than favouring boreal‐breeding systems that form the basis of other terminologies (Pyle et al 2022).…”