MOL TS, PLUMAGES, AND AGE CLASSES OF PASSERINES AND "NEAR-PASSERINES": A BANDER'S OVERVIEW Kenneth M. Burton 1207 Gassoway Rd. McKinleyville CA 95519 [email protected] ABSTRACT A thorough understanding of molts and plumages additional confusion because the reference and their relation to age classes is fundamental to materials do not yet reflect it. accurate and precise age determination of banded birds. Molt strategy and time of year affect the I see the acquisition of skills necessary for age level of precision possible when determining a determination as a three-step process. The first bird's age. This paper describes, with schematic step (the focus of this paper) is to develop a illustrations of the first few calendar years in the thorough understanding of molt and plumage lives of six representative species, some of the sequences and the relationships of plumages to variation in molt strategy and its effects on age­ age classes. The second, entirely contingent on class assignment. I use recently proposed the first, is to master Pyle (1997a) and other modifications to standard Humphrey-Parkes molt relevant literature so that information can be terminology. The molt strategies exhibited by all extracted efficiently. The third is to learn to apply North American passerines and "near-passerines" the first two, steps in the field to arrive at accurate, are presented in an appendix. precise, and speedy age determinations. One must know what to look for and where and be able to INTRODUCTION recognize it and interpret it correctly. Accurate (correct) and precise (specific) age This paper provides an overview and schematic determination of birds in the hand is a necessary diagrams of the molts, plumages, and age classes element of virtually any meaningful banding project. of six representative North American "near­ Recently published reference materials (e.g., Pyle passerines" (Columbiformes through Piciformes) 1997a,b; Williamson 2001; Froehlich 2003) provide and passerines. It is intended to reinforce these tools for North American land-bird banders to concepts for experienced banders and serve as a .. discriminate among plumages and age classes of learning tool for beginners and a teaching tool for many species. In my observation, however, too trainers. It is restricted in scope to the 397 species few banders have a sufficient grasp of the described in Pyle (1997a) and currently recognized .. relationships among molts, plumages, and age by the American Ornithologists' Union; no inference classes, or the effects of variation in molt strategy to species beyond this group is intended. I make on age determination, to apply these tools no attempt to explain the ecological or physiological consistently. A modification to the Humphrey­ constraints driving variation in molt strategy; for Parkes (H-P) molt terminology (Humphrey and information on these topics see Howell (2003a). I Parkes 1959) proposed recently by Howell et al. use the modified terminology (Howell et al. 2003), (2003) and rapidly gaining acceptance within the with references to the more familiar terminology ornithological community, has the potential to add as needed. Oct.- Dec. 2006 North American Bird Bander Page 175 TERMINOLOGY AND BASIC PRINCIPLES The first plumage of all young birds is the natal Molts and plumages down (which .I abbreviate ND); there may be two A molt is a hormonally induced, essentially or more sets of natal down or virtually none. symmetric growth of feathers. Adventitious, or Thereafter, each annual cycle is initiated by a molt accidental, loss and replacement of feathers is not that is nearly always complete; it is known as the considered a molt, although it may be helpful in prebasic molt (PB) and produces basic plumage. age determination. Humphrey and Parkes (1959) In the first cycle, the first prebasic (also called define a plumage as the set of feathers produced prejuvenal) molt (PJ) replaces the natal down with by a molt and the entire set of feathers possessed the first basic (juvenal) plumage (abbreviated Juv), by a bird at any given time (often produced by which includes the bird's first set of contour and multiple molts) as the feather coat. In popular flight feathers. All molt strategies are alike in these usage, however, the former term has acquired the respects; the differences among them concern the latter meaning. In this paper, the term "plumage" number, timing, and extent of additional molts (in quotes) indicates a feather coat consisting of within each cycle. multiple generations of feathers. The entire appearance of a bird, including non-plumage Molt strategies characteristics, is known as its aspect. Plumages The term molt strategy refers to the frequency, are not produced by feather wear; thus, a bird that timing, and extent of molts throughout a bird's life. loses the dull tips of its fresh feathers during the Howell and Corben (2000) and Howell et al. (2003) winter is not acquiring a new plumage. Conversely, defined four underlying molt strategies, one of a molt does not necessarily change a bird's which is exhibited by every bird species: the plumage or appearance; it may produce a fresher Simple Basic Strategy (SBS), Simple Alternate version of the previous plumage or the differences Strategy (SAS), Complex Basic Strategy (CBS), between the old and new plumages may be too and Complex Alternate Strategy (CAS). They subtle for us to see. The name of each molt is the are described in less technical terms by Howell name of the plumage it produces plus the prefix (2003b) and provide a convenient means of 'pre'. grouping and contrasting strategies, even using traditional H-P terminology. Molts, when they occur, vary considerably in extent. Complete molts include all the feathers. The "alternate" strategies differ from the "basic" Incomplete molts include the contour (body) strategies in the presence of a prealternate molt feathers and some of the flight feathers (primaries (PA) (and, of course, an alternate plumage) in and their coverts, secondaries, and rectrices). each cycle. The "complex" strategies differ from Partial molts include contour feathers (typically the "simple" strategies in the presence of at least including secondary coverts) but no flight feathers one "extra" molt and plumage, the preformative (with the frequent exception of tertials and central molt(s) (PF) and formative plumage(s), unique rectrices, which may more accurately be to the first cycle. The main PF is the molt considered body feathers). Limited molts include designated '1st PB' or 'PB: HY' in Pyle (1997a) and only some contour feathers and typically not Froehlich (2003). All passerines and virtually all secondary coverts. If a molt does not occur at all, the "near-passerines" exhibit complex strategies .. it is termed absent. For more complete (Pyle 1997a, Howell et al. 2003); only two species descriptions of these molt extents and when they considered here are known to follow the SBS and .. are likely to occur, see Pyle (1997a). A molt limit none shows the SAS. Molt strategies are defined (also known in the UK as a molt contrast) is the at the species rather than the individual level (P. boundary, produced by a less-than-complete molt, Pyle, pers. comm.); thus, although many individuals between newer and older feathers; it is a plumage of species that are classed as alternate strategists character that illustrates the extent of a previous do not undergo PAs, they remain alternate molt. strategists because the species has evolved the PA as part of its molt repertoire. Page 176 North American Bird Bander Vol. 31 No. 4 Age classes As a rule, banders should be as precise as possible Fundamentally, assigning a bird to an age class is without sacrificing accuracy and thus should a matter of ascertaining whether it is young (in this attempt·to assign each bird to the most precise group, usually first-cycle) or .adult based on the age class possible for the time of year at which it is presence or absence, respectively, of juvenal captured. It is essential to understand the nested features. The North American Banding Program relationship of the age classes (Fig. 1). HY and uses the calendar-year approach, which AHY are subsets of the imprecise category, U. SY superimposes an artificial time system onto birds' and ASY, in turn, are subsets of AHY, while TY life cycles: Under this system, birds change age and ATY are subsets of ASY. Lis not considered classes due to certain physiological events, such a subset of U because it is always distinctive. as molts; and also to change of. calendar year, an event of no significance to them. Age classes are CASE STUDIES usually designated with acronyms or numeric codes. I have devised artificial groupings of species that share certain aspects of molt extent and timing Very young birds, old enough to be banded but such that, collectively, they illustrate the relevant not yet capable of sustained flight, are called local spectrum of molt terminology and the effects of molt (Lor 4). Birds capable of sustained flight but still strategy on age class assignment. The following clearly in their first calendar year are called hatch­ six examples illustrate what I think are the most year (HY or 2). Those clearly in their second important aspects of passerine and "near­ calendar year are called second-year (SY or 5), passerine" molt strategies, beginning with the two those in their third calendar year are third-year most common strategies. For each one I have (TY or 7), etc. Less-precise categories exist for chosen as an example a species that represents it birds that cannot be assigned to a specific year: without exception; that is, all individuals of that after-hatch-year (AHY or 1) birds are at least in species always exhibit the strategy in question.