Development syndromes in New World temperate and tropical songbirds

Abstract

We studied avian development in 49 to 153 species of temperate and tropical New World passerine birds to determine how growth rates, and incubation and nestling periods, varied in relation to other life-history traits. We collected growth data and generated unbiased mass and tarsus growth rate estimates (mass n = 92 species, tarsus n = 49 species), and measured incubation period (n = 151) and nestling period (n = 153), which we analyzed with respect to region, egg mass, adult mass, clutch size, parental care type, nest type, daily nest predation rate (DMR), and nest height. We investigated covariation of life-history and natural-history attributes with the four development traits after controlling for phylogeny. Species in our lowland tropical sample grew 20% (incubation period), 25% (mass growth rate), and 26% (tarsus growth rate) more slowly than in our temperate sample. Nestling period did not vary with respect to latitude, which suggests that tropical songbirds fledge in a less well-developed state than temperate species. Suboscine species typically exhibited slower embryonic and post-embryonic growth than oscine passerines regardless of their breeding region. This pattern of slow development in tropical species could reflect phylogenetic effects based on unknown physiological attributes. Time-dependent nest mortality was unrelated to nestling mass growth rate, tarsus growth rate, and incubation period, but was significantly associated with nestling period. This suggests that nest predation, the predominant cause of nest loss in songbirds, does not exert strong selection on physiologically constrained traits, such as embryonic and post-embryonic growth, among our samples of temperate and lowland tropical songbird species. Nestling period, which is evolutionarily more labile than growth rate, was significantly shorter in birds exposed to higher rates of nest loss and nesting at lower heights, among other traits. Differences in life-history variation across latitudes provide insight into how unique ecological characteristics of each region influence physiological processes of passerines, and thus, how they can shape the evolution of life histories. While development traits clearly vary with respect to latitude, trait distributions overlap broadly. Life-history and natural history associations differ for each development trait, which suggests that unique selective pressures or constraints influence the evolution of each trait.

Fig 1. Nestling period (d) of open-cup nesting species by region.

Fig 2

Relationships between mass growth rate and (A) nestling period, (B) tarsus growth rate (k), and (C) incubation period. Plot (D) depicts the relationship between incubation period and nestling period. Each point represents a particular species. Latitudinal regions are distinguished by dark gray (temperate species) or light gray (tropical), while Suborders are indicated by circles (Passeri or oscines) and triangles (Tyranni or suboscines). We have highlighted several groups (sparrows, longspurs, and warblers) that seem to be driving some of the observed associations. Species are labeled by their 4 letter alpha codes (see https://doi.org/10.7267/m613n4425). Sparrow species include atsp (American tree sparrow), chsp (chipping sparrow), eato (eastern towhee), fisp (field sparrow), savs (savannah sparrow), rcsp (rufous-collared sparrow), and wcsp (white-crowned sparrow). Longspurs include cclo (chestnut-collared longspur), lalo (lapland longspur), and mclo (McCown’s longspur). Warblers are amre (American redstart), bwwa (blue-winged warbler), coye (common yellowthroat), kewa (Kentucky warbler), nowa (northern waterthrush), wiwa (Wilson’s warbler), and ywar (yellow warbler).

Fig 3

Development traits by region A) Mass Growth Rate k, B) Tarsus Growth Rate, k, C) Incubation Period, d, D) Nestling Period, d.

Fig 4

Relationships between DMR on the x-axis and A) Mass Growth Rate, k; B) Tarsus Growth Rate, k; C) Incubation Period, d; or D) Nestling Period, d, on the y-axis. Each point represents a different species. Temperate species are depicted in dark gray and tropical species in light gray, while nest types are indicated by circles (cavity), triangles (open-cup), or squares (enclosed-cup). Outliers with high DMR are two temperate open-cup nesting species, Bombycilla cedrorum (cedw) and Melospiza melodia (sosp).