Life‐history variation of a neotropical thrush challenges food limitation theory

Abstract

Since David Lack first proposed that birds rear as many young as they can nourish, food limitation has been accepted as the primary explanation for variation in clutch size and other life-history traits in birds. The importance of food limitation in life-history variation, however, was recently questioned on theoretical grounds. Here, we show that clutch size differences between two populations of a neotropical thrush were contrary to expectations under Lack's food limitation hypothesis. Larger clutch sizes were found in a population with higher nestling starvation rate (i.e. greater food limitation). We experimentally equalized clutches between populations to verify this difference in food limitation. Our experiment confirmed greater food limitation in the population with larger mean clutch size. In addition, incubation bout length and nestling growth rate were also contrary to predictions of food limitation theory. Our results demonstrate the inability of food limitation to explain differences in several life-history traits: clutch size, incubation behaviour, parental feeding rate and nestling growth rate. These life-history traits were better explained by inter-population differences in nest predation rates. Food limitation may be less important to life history evolution in birds than suggested by traditional theory.

Causes of reduced clutch size in a tidal marsh endemic

“…This scenario leads to a number of testable predictions (Table 1: P1-6). Within each subspecies, predation risk should be highest during the stage of offspring development with the most parental activity around the nest (P1), and parental activity should be higher around nests with more offspring (P2: Ferretti et al 2005). Furthermore, nest attendance should be lower, on average, in the coastal population in order to reduce detection by predators (P3: Eggers et al 2005;Fontaine and Martin 2006), which may in turn reduce nestling growth (Nolan et al 2001) or increase the mass of food carried per provisioning trip (P4: Martin et al 2000).…”

“…Clutch size is influenced by a number of phylogenetic and environmental constraints (Martin 2004), whose hierarchical organization (Ghalambor and Martin 2001) should allow for clutch size predictions in specific populations. To understand the interactions between these constraints, however, it is necessary to examine multiple, phylogenetically controlled pairs of species or populations in a variety of environments (Ferretti et al 2005;Martin et al 2000). Here we present a single such contrast between two subspecies of the swamp sparrow, Melospiza georgiana, at study sites 319 km apart at a similar latitude (39.6°N vs. 39.4°N), yet varying in elevation (800 m), predation risk, and climate.…”

Flexibility in Nest-Site Choice and Nesting Success of Turdus rufiventris (Turdidae) in a Montane Forest in Northwestern Argentina

“…(Ridgely andTudor 1989, de la Peña andRumboll 1998), and is one of the few native forest species that inhabits semi-urban locations (de la Peña andRumboll 1998, Ferretti et al 2005). The ability of members of the genus Turdus, including T. rufiventris (e.g., de la Peña and Rumboll 1998, Ferretti et al 2005, to live in human-disturbed areas makes them good model species to study how birds adapt to habitat disturbance. Understanding the adaptability of species to disturbance is becoming increasingly important as anthropogenic habitat alterations become increasingly common and intact habitats increasingly rare (Pimm et al 2001).…”

Reproductive Success of the Creamy-Bellied Thrush in a Southern Temperate Zone

“…Thus, they are an excellent model for study of life history evolution, breeding biology, and latitudinal variation among related species occupying different ecosystems. However, there are only a few comparative studies (Martin et al 2000, Ferretti et al 2005 and the available information is biased to north temperate species. Most information on breeding biology for species of Turdus in Argentina comes from studies in the Pampas and Yungas (e.g., Martin et al 2000, Sackmann and Reboreda 2003, Ferretti et al 2005.…”

“…However, there are only a few comparative studies (Martin et al 2000, Ferretti et al 2005 and the available information is biased to north temperate species. Most information on breeding biology for species of Turdus in Argentina comes from studies in the Pampas and Yungas (e.g., Martin et al 2000, Sackmann and Reboreda 2003, Ferretti et al 2005. There are no studies available for populations from semi-arid areas of western Argentina (but see Mezquida and Marone 2001 for other passerine species).…”