Evidence of breeding activity of subadult Turdus thrushes in Argentina

Abstract

A substantial body of research has shown that a bird's reproductive performance can vary considerably over its lifetime (reviewed by Newton 1989). Reproductive success in passerines generally improves with age (e.g., Förschler & Kalko 2006), with older birds initiating nesting activities earlier, having larger broods, and lower rates of nest failure (Robertson & Rendell 2001). Females that breed in their first year tend to raise fewer offspring per season than older females (Nol & Smith 1987), although nest success eventually diminishes after peaking in middle-aged females (Robertson & Rendell 2001). Reproductive success is generally lower when one member of a breeding pair is younger, whereas experienced pairs, consisting of two adults, show higher reproductive performance (Geslin et al. 2004). Thus, the first year in a bird's life appears to be generally characterized by low reproductive success (Förschler & Kalko 2006). Evaluating how age influences reproductive success is important for understanding the evolution of life history