Breeding Seasons, Molt Patterns, and Gender and Age Criteria for Selected Northeastern Costa Rican Resident Landbirds

The Wilson Journal of Ornithology 121(3):556–567, 2009 BREEDING SEASONS, MOLT PATTERNS, AND GENDER AND AGE CRITERIA FOR SELECTED NORTHEASTERN COSTA RICAN RESIDENT LANDBIRDS JARED D. WOLFE,1,2,4 PETER PYLE,3 AND C. JOHN RALPH2 ABSTRACT.—Detailed accounts of molt and breeding cycles remain elusive for the majority of resident tropical bird species. We used data derived from a museum review and 12 years of banding data to infer breeding seasonality, molt patterns, and age and gender criteria for 27 common landbird species in northeastern Costa Rica. Prealternate molts appear to be rare, only occurring in one species (Sporophila corvina), while presupplemental molts were not detected. Most of our study species (70%) symmetrically replace flight feathers during the absence of migrant birds; molting during this period may limit resource competition during an energetically taxing phase of the avian life-cycle. Received 30 August 2008. Accepted 19 February 2009. Temporal patterns of molt and breeding sea- of the avian life cycle, but other factors including sonality are largely unknown for many resident climate and resource availability may also affect tropical species (Dickey and van Rossem 1938, timing of molt (Aidley and Wilkinson 1987, Snow and Snow 1964, Snow 1976) in contrast to Bensch et al. 1991, Jones 1995). Little has been Nearctic-Neotropic migrants (hereafter ‘mi- published concerning temporal patterns of molt grants’). One might assume differential molt among resident tropical species in relation to sequences and extent between latitudes given competition from overwintering migrants despite different natural histories of resident tropical birds continued interest in factors influencing timing of in relation to their migrant counterparts. However, molt (Snow and Snow 1964). Given the energet- preliminary studies indicate that most neotropical ically taxing nature of molt, we believe temporal residents exhibit molt strategies similar to those in patterns of molt among resident species may be temperate latitudes (Dickey and van Rossem influenced by resource competition associated 1938, Diamond 1974, Foster 1975, Prys-Jones with presence or absence of migrant birds. Molt is 1982, Pyle et al. 2004, Ryder and Wolfe 2009, a critical facet of avian natural history and molt Wolfe et al. 2009). These strategies include partial ecology has utilitarian characteristics which aid in to incomplete preformative molts and complete understanding population structure and demo- prebasic molts that often occur in June–Septem- graphic trends. ber, following breeding. Capture-recapture, capture-telemetry, and cap- Molt and breeding events are energetically ture-observational data are often used to quantify demanding and, for the most part, independent demographic trends of resident neotropical land- phases of the avian life cycle (Snow and Snow birds (Greenberg and Gradwohl 1997, Sandercock 1964, Payne 1972, Avery 1985, Pyle 1997). et al. 2000, Cohen and Lindell 2004). Accurately However, overlap between molt and breeding modeling population structure requires methodol- has been documented in a few temperate landbirds ogy pertaining to identification of age and gender (Bancroft and Woolfenden 1982, Thompson and classes. Thus, understanding the extent and Slack 1983, Zaias and Breitwisch 1989, Hemborg sequence of molt for a given species is critical 1999) and some resident tropical landbirds for accurate age classification and subsequent (Dickey and van Rossem 1938, Snow and Snow demographic analyses. 1964, Foster 1975, Avery 1985). Breeding and The Tortuguero Integrated Bird Monitoring molt seasonality influence the temporal dynamics Project (TIBMP) was established in 1994 on the northern Caribbean coast of Costa Rica, near the 1 Humboldt State University, Wildlife Department, 1 village of Tortuguero, to monitor migrants as well Harpst Street, Arcata, CA 95521, USA. as resident bird populations through constant- 2 USDA Forest Service, Pacific Southwest Research effort mist-netting (Ralph et al. 2005). We used Station, Redwood Sciences Laboratory, 1700 Bayview 12 years of banding data from TIBMP coupled Drive, Arcata, CA 95521, USA. 3 Institute for Bird Populations, P. O. Box 1346, Point with a review of museum specimens to provide Reyes Station, CA 94956, USA. information on molt and breeding seasonality, and 4 Corresponding author; e-mail: [email protected] useful criteria for identification of age and gender 556 Wolfe et al. N MOLT AND BREEDING CYCLES OF COSTA RICAN BIRDS 557 for 27 resident bird species of northeastern Costa Formative-plumaged individuals are often identi- Rica. fiable by retained primary coverts which typically lack distinctive edging, luster, and are typically METHODS more worn in relation to definitive primary Nine monitoring sites were near the village of coverts and contrast in wear with replaced greater Tortuguero on the northeast coast of Costa Rica in coverts. Definitive flight feathers are typically Limon Province (83u 319 70 W, 10u 339 510 N; more truncate in relation to retained juvenile elevation 0–20 m). One ‘central’ station was flight feathers. We specifically looked for each of operated at least five times every 10 days while these criteria for banded birds (using standardized the remaining ‘satellite’ stations were operated at data forms) and museum specimens. least once every 10 days. Between 10 and 15 12- Molt and age terminology, including standard m mist nets were operated at each site by JDW abbreviations, follow those of Pyle (1997) as and others from August to May, 1994–2006 modified by Howell et al. (2003). The first basic (Ralph et al. 2005). Species studied were selected plumage is referred to as juvenile plumage (Juv), based on high capture rates during preliminary followed by the preformative molt (PF), first banding efforts (1994–2000). Protocols pertaining prealternate molt (PA1; if existing in the species), to captured birds follow Ralph et al. (1996). second prebasic molt (PB2), and definitive Banding efforts were not sustained during June prealternate (DPA; if existing) and definitive and July. Breeding seasonality during these prebasic (DPB) molts. Primaries and primary months was inferred based on brood patch and coverts are numbered from the innermost (prima- cloacal protuberance data obtained during May ry 1) to the outermost (primary 9 or 10), and August, juxtaposition of the prebasic molt, secondaries and the greater coverts are numbered and presence of juveniles. Recaptured individuals from the outermost (secondary 1) to the innermost in many cases were used to verify age; our sample tertial, and rectrices are numbered from the sizes include recaptured individuals as well. central pair (rectrix 1) to the outermost pair Findings based on banded birds at Tortuguero (rectrix 5 or 6). ‘‘Partial’’ for molt extent, were augmented by those from specimens exam- indicates that no flight feathers (primaries, ined at the National Museum of Natural History primary coverts, secondaries, or rectrices) were (USNM) by Pyle in early August 2001. All replaced (except the tertials or central rectrices in specimens from selected species collected in some individuals) and ‘‘incomplete’’ indicates southern Mexico through northern Panama were that some but not all flight feathers were replaced. examined and, in a few cases, specimens collected An ‘‘eccentric molt pattern’’ refers to an incom- in South America were also examined. Ages of plete molt in which molt of primaries begins at a birds were inferred when collected and, in many central feather (other than primary 1) and cases, there were no specimens collected while in proceeds distally, and molt of secondaries begins active molt. Plumage succession and molt timing with a central feather (other than secondary 1) and could often be assumed based on molt limits and proceeds proximally to the tertials (Pyle 1997, extent of feather wear (Pyle 1997). Criteria Pyle et al. 2004). The ‘‘typical molt sequence’’, developed with specimens in 2001 were con- which can be incomplete during preformative firmed or re-examined with analysis of banding molts, refers to a molt proceeding distally from data from 1994 to 2006. Banding/specimen data primary 1 and proximally from secondary 1, as is were augmented with information provided by typical of definitive prebasic molts. Stiles and Skutch (1989). Age classification follows the calendar-based The partial to incomplete nature of the system described by Pyle (1997). Age codes preformative molt in most neotropical resident include HY (hatching year), indicating a bird in landbird species can be used to facilitate accurate the calendar year of its hatching; SY (second age-class categorization of captured birds (Pyle year), indicating a bird in its second calendar year 1997). Feather characteristics, regarding molt (HY/SY indicates a bird in its first plumage cycle, limits and retained juvenile (HY) plumage among being HY until 31 Dec and SY after 1 Jan); TY tropical residents, appears to be similar to those of (third year), indicating a bird in its third calendar temperate species. For example, retained juvenile year; AHY (after-hatching year), indicating a bird retrices are often duller in coloration, more worn in at least its second calendar year; ASY (after- (in relation to definitive retrices) and tapered. second year), indicating a bird in at least its third 558 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 121, No. 3, September 2009 calendar year; ATY (after-third year), indicating a nape, and buff or whitish tipping to back feathers, bird in at least its fourth calendar year; and U tertials, and most wing coverts, absent in definitive (unknown), indicating a bird that may or may not plumage. More pointed rectrices with a deeper be in the calendar year of birth. Month ranges in white triangle at the tip (.5 mm along shaft) and parentheses indicate the timing for which ages can brownish along outer webs not extending toward be identified; e.g., ‘‘HY/SY (Oct–Sep)’’ indicates the shaft may represent HY/SYs; more study a bird with indicative criteria, usually based on an needed. Bill corrugations present in HY/SYs aspect of juvenal or formative plumage and the year-round.

Load more