Journal of Avian Biology 43: 141–154, 2012 doi: 10.1111/j.1600-048X.2011.05574.x © 2012 Th e Authors. Journal of Avian Biology © 2012 Nordic Society Oikos Subject Editor: Wolfgang Goymann. Accepted 28 December 2011 The phenology of molting, breeding and their overlap in central Amazonian birds Erik I. Johnson , Philip C. Stouffer and Richard O. Bierregaard, Jr E. I. Johnson ([email protected]) and P. C. Stouff er, School of Ren. Nat. Res., LSU AgCenter and Louisiana State Univ., Baton Rouge, LA 70803, USA. EIJ also at: Nat. Audubon Soc., 6160 Perkins Rd., suite 135, Baton Rouge, LA 70808, USA. – R. O. Bierregaard, Jr, Dept of Biol., Univ. of North Carolina, Charlotte, NC 28223, USA. Th e energetically challenging periods of molting and breeding are usually temporally separated in temperate birds, but can occur simultaneously in tropical birds, a condition known as molt – breeding overlap. Here, we document great variation in the timing and duration of molting and breeding, and in the extent of molt – breeding overlap, among 87 species of understory passerines in central Amazonia. We analyzed molt and breeding from 26 871 birds captured over a 30-yr period near Manaus, Brazil. Although most species typically bred during the late dry season (about October through January), many thamnophilids apparently bred year-round, whereas a few other species from a variety of families bred mainly during the wet season (about January through May). Of all breeding birds with an active brood patch, 12.7% were simultane- ously molting. Molt – breeding overlap was more frequently observed among suboscines (13.3%), especially thamnophilids (23.0%), than oscines (6.4%). Some families had Ͻ 5% molt – breeding overlap frequency, including Tyrannidae (4.4%), Tityridae (0.0%), Pipridae (1.5%), Turdidae (0.0%), and Th raupidae (0.0%), indicating that not all tropical species exhibit molt – breeding overlap. Among 31 well-sampled species (n Ն 15 brood patches), variation in molt – breeding overlap fre- quency was positively correlated with each species ’ average duration of fl ight feather replacement (range 98 – 301 d). We also measured feather growth rates of individual birds in nine species; in fi ve of these, slower-growing feathers increased with an individual ’ s probability of having molt – breeding overlap. Among furnariids, molt – breeding overlap occurred either at the beginning or end of the molt cycle, suggesting that physiological mechanisms typically separate molting from breed- ing. Th amnophilids showed a much diff erent pattern; molt – breeding overlap occurred at any stage of feather replace- ment, apparently not regulated to be independent of breeding. Th ese results reveal substantial life-history variation among Amazonian birds. Future work to resolve the physiological regulation of molting and breeding in tropical birds will greatly contribute to understanding these patterns and their relevance to avian diversity. Annual life history events in birds that demand especially known about the timing of these events in tropical commu- high energy expenditure include breeding, molting, and nities, especially in contrast to temperate communities (Pyle migration, and these are typically separated temporally to 1997, Dawson 2008). minimize their overlap (Drent and Daan 1980, Kjell é n For tropical species that do not migrate, temporal 1994, Murphy 1996). Because energy available to birds is constraints on molting and breeding should be reduced. limiting, trade-off s between successful breeding, molting, Paradoxically, individuals of many tropical species are and migration are often apparent. For example, high repro- thought to regularly molt and breed simultaneously, referred ductive investment can delay molt, decrease feather quality, to as molt – breeding overlap (Snow and Snow 1964, Foster and reduce parental survival (Siikam ä ki et al. 1994, Nilsson 1975, Avery 1985, Astheimer and Buttemer 1999, Marini and Svensson 1996, Dawson et al. 2000). Conversely, molt- and Dur ã es 2001). It is not clear what drives increased ing early can reduce fecundity, but increase parental survival molt – breeding overlap in some tropical birds, but reduced (Morales et al. 2007). Furthermore, costs associated with physiological demands due to a slower-paced lifestyle molting are believed to prevent overlap with migration; some appears to correlate with its occurrence (Foster 1974, migratory species even temporarily arrest molt until migra- Franklin et al. 1999, Wingfi eld 2005). Tropical birds tion is completed (Stresemann and Stresemann 1966, Pyle typically lay fewer eggs per clutch (usually just two; 1997, Leu and Th ompson 2002, P é rez and Hobson 2006). Skutch 1969, Kulesza 1990, Young 1994, Martin et al. Th us, the timing of these life-history events is presumably 2000), have reduced maximum gonad size and hormonal subject to strong evolutionary pressures and is optimized concentrations (Stutchbury and Morton 2001, Wikelski through natural selection to maximize fi tness (Dawson et al. et al. 2003a, Goymann et al. 2004, Hau et al. 2010), 2000, Ricklefs and Wikelski 2002, Moreno 2004). Little is a lower metabolic rate (Ricklefs 1976, Weathers 1979, 141 Wikelski et al. 2003b, Jetz et al. 2008), and a prolonged Methods molt (Helm and Gwinner 1999, Ryder and Wolfe 2009). High nest predation rates resulting in multiple nesting Study site attempts (Skutch 1949, Kulesza 1990, Ferretti et al. 2005, Roper 2005, but see Snow and Snow 1963, Oniki 1979, We conducted our study at the Biological Dynamics of Martin 1995, Robinson et al. 2000) coupled with decreased Forest Fragments Project (BDFFP), which is located seasonality and more constant resource availability (Lack about 80 km north of Manaus, Brazil (2 ° 30 ′ S, 60 ° W). Th is 1947, Ashmole 1963, Cody 1966, Ricklefs 1980, Hahn landscape contains largely undisturbed terra fi rme lowland et al. 1992, Martin 1996) may at least partially explain tropical rainforest, especially to the north of our study site. this reduced-paced life style with extended molting Th e forest canopy is 30 – 37 m tall with emergents reaching and breeding seasons. Under these circumstances, molt – 55 m. Th e understory is relatively open and is dominated by breeding overlap may not severely reduce fecundity or palms. Annual rainfall is approximately 2500 mm (ranging fi tness in tropical species compared to temperate species from 2000 to 3500 mm) with a dry season typically last- (Foster 1974, Slagsvold and Dale 1996, Hemborg and ing from June to November (Stouff er and Bierregaard 1993, Lundberg 1998, Hemborg 1999, Hemborg et al. 2001). Laurance 2001). Th e site has some topography, especially Tropical forest birds show great variation in foraging near streams, and varies in elevation from 50 to 100 m. Soils strategy, social system, and microclimate use (Karr 1971, are generally nutrient-poor sandy or clay-rich ferrasols, typi- Terborgh et al. 1990, Stutchbury and Morton 2001). Th e cal of the region (Sombroek 2000). humid lowland rainforests of the central Amazon contain a Th e BDFFP is well-known for its studies of forest frag- diverse avian community with great variation in life history mentation (Bierregaard et al. 2001) including considerable strategies, providing an ideal opportunity to study within- eff orts to document the natural avian community in mature community variation in molting and breeding phenology undisturbed forest (Cohn-Haft et al. 1997, Johnson et al. (Cohn-Haft et al. 1997, Johnson et al. 2011). For example, 2011), but also includes extensive monitoring and research in a single 100-ha patch of undisturbed central Amazonian at intact continuous forest that act as control sites. Here we forest, over 200 species have been found (Johnson et al. use a long-term mist-netting database of this research from 2011). Such diversity in life history strategies may also result 1979 through 2009 that includes over 60 000 captures and in variation in molt – breeding overlap frequency among spe- 324 860 mist-net hours. Th is database has been accrued from cies, but few large datasets (Poulin et al. 1992, Marini and 11 forest fragments, including 1/4 to 10 yr of pre-isolation Dur ã es 2001, Wolfe et al. 2009) are available to examine sampling (median 1 yr; Bierregaard et al. 2001), as well as the variation of molting and breeding phenologies within a 34 continuous forest sites. Mist-nets were typically open tropical community. from 08:00 to 14:00 and the number of 12 ϫ 2-m mist In this paper, we present the phenology of breeding nets used at each site was dependent on plot or fragment size using brood patch data, molting using primary feather molt with eight mist nets in 1-ha plots, 16 nets in 10-ha plots, data, and their overlap in a near-equatorial community and 48 nets in 100-ha plots. Beginning in 1991, an addi- of understory forest birds in Amazonian Brazil, as well as tional 16 nets were placed around the borders of fragments explore ecological factors that covary with these patterns. and interior forest plots. Fragments were sampled year- We fi rst predicted that the frequency of molt – breeding round 1 – 16 times (median 5 times) per year in 1979 – 1992, overlap among species would vary among species accord- and 2000, and during the dry seasons of 2007 and 2009. ing to their ecology and taxonomy if this trait was adap- Each continuous forest site has been sampled less con- tive. We then examined correlates of molt – breeding overlap sistently than the fragments, but collectively account for frequencies with the expectation that increased frequency 62% of mist-net hours and 67% of all captures. Although of molt – breeding overlap would correlate with longer molt some uncertainty remains about how fragmentation poten- duration and decreased fl exibility in timing of molt initia- tially impacts the phenology of molting, breeding, and tion. We also predicted that individual birds would increase their overlap (Results), the majority of our data are derived their probability of having molt – breeding overlap when from continuous forest sites.