Molting while breeding? Lessons from New World Tyrannus Flycatchers

Abstract

Songbirds must annually undergo two energetically demanding but important activities: breeding and feather molt. Due to the high energetic investment that each demands, these two events are generally not carried out simultaneously. However, substantial variation in the level of annual reproductive investment among populations may result in variation in molt-breeding overlap between them. With the goal of understanding whether different songbird populations overlap molt and breeding, and, if so, to determine directions for research on the potential tradeoffs involved, we describe the relationship between clutch size, molt, and energetic condition within a genus of New World Flycatchers (Tyrannus). Of 219 Flycatchers sampled, only one individual molted flight feathers while breeding, suggesting that molting flight feathers and breeding simultaneously is too energetically expensive at any clutch size. However, some Flycatchers molted body feathers during the breeding season. When we tested for an effect of clutch size, sex and energetic condition on body molt intensity during the breeding season, only clutch size and sex had significant effects, with a negative effect of clutch size on body molt intensity in males but not in females. Based on these results, we develop a set of hypotheses to guide future studies on the potential tradeoffs between investment in reproduction and molt.

Weak breeding seasonality of a songbird in a seasonally arid tropical environment arises from individual flexibility and strongly seasonal moult

“…We hypothesize that although individuals are capable of breeding year‐round, birds which complete a successful first breeding attempt are unlikely to overlap nesting and moult (Jahn et al . ). A more common scenario in our study area is to find females with brood patch scores of 4 and 5 (post‐nesting stages) already starting wing moult or a few pairs initiating breeding attempts after September when moult is largely complete (Fig.…”

Breeding latitude predicts timing but not rate of spring migration in a widespread migratory bird in South America

“…Fork‐tailed Flycatchers are known to track rainfall during winter (MacPherson et al, ), arriving at the wintering grounds in northern South America at the beginning of the wet season, which peaks in July and August (Poveda, Waylen, & Pulwarty, ) and where Fork‐tailed Flycatchers undergo an annual flight feather molt (Jahn, Giraldo, et al, ; Jahn, Seavy, et al, ). Winter represents a critical period during which they must properly time flight feather molt prior to spring migration, since Fork‐tailed Flycatchers generally avoid molting and migrating simultaneously (Jahn et al, ). Given that northern South America is susceptible to notably lower rainfall levels in some years (i.e., during the “El Niño” phase of the El Niño/La Niña climatic cycle, Poveda et al, ), understanding the relationship between interannual variation in food resource availability, which is key to completing feather molt (Jahn, Giraldo, et al, ; Jahn, Seavy, et al, ), and the timing of events in the flycatcher's annual cycle, will provide novel insights into the constraints molding the annual cycle and population dynamics of this and other species migrating within South America.…”

Drivers of wing shape in a widespread Neotropical bird: a dual role of sex-specific and migration-related functions

“…We captured and measured migratory flycatchers during the breeding season (Sep to Jan; Marini et al 2009;Jahn et al 2017), at the following sites ( Fig. 1 We measured non-migratory flycatchers (T. s. monachus) during the breeding season (Mar to Apr; Jahn et al 2017) at the following sites ( Fig.…”

“…Data collection: Breeding flycatchers were captured near their nests using methods in Jahn et al (2017) and banded with an individually numbered metal band and up to three Darvic color bands. Primary feathers of juvenile flycatchers lack notches, whereas adults (i.e., individuals that are at least 1 year old) have notches at the tips of their primary feathers (Pyle 1997;Jahn et al 2016;Fig.…”