Breeding Strategies of a Socially Monogamous Neotropical Passerine: Extra-Pair Fertilizations, Behavior, and Morphology

Abstract

Blue-black Grassquits (Volatinia jacarina) are small, granivorous, Neotropical birds that are abundant in central Brazil. During the reproductive season, the socially monogamous males acquire a blue-black plumage and defend very small, clustered territories that resemble leks. They execute a conspicuous courtship display that consists of a leap, revealing white under-wing patches, synchronized with a vocalization. We collected data on the morphology and behavior of banded males and characteristics of their territories to determine how these factors may influence acquisition of mates and nesting. For a second group of birds in the area, we used microsatellite genotyping to test the breeding synchrony hypothesis, which predicts that tropical species that breed synchronously should exhibit high rates of extra-pair fertilization (EPF). We found that males that successfully formed a pair bond differed from unsuccessful males in their behavior, but not in morphological attributes or territory features. Successful males spent more time in their territories, executed displays for longer periods and at greater rates, and their display leaps were higher. These results point to the greater importance of behavior relative to other factors in the successful reproduction of Blue-black Grassquit males. In the second group of birds, EPFs occurred in 63% of 11 nests and involved 50% of the 20 chicks sampled. This exceptionally high incidence of EPF in the small sample analyzed occurred in diverse contexts, including intraspecific parasitism and quasi-parasitism, a rare type of maternity loss where the resident female is parasitized by other females that were fertilized by the resident male. A short and highly synchronized breeding season, clustered breeding in small territories, and granivorous habits may contribute to the high rates of EPF in this tropical species.

Dangerous love? Predation risk does not affect female mate choice in blue‐black grassquits

“…Females then pair with territorial males, apparently ignoring most male attributes (Dias et al, ). They also appear to choose their mates disregarding male health (Aguilar et al, ), territory quality (Almeida & Macedo, ; Carvalho et al, ), and predation risk (present study). Successfully paired males in the wild have been shown to spend more time in their territories, display for longer periods and at greater rates, and produce higher leaps in their displays (Carvalho et al, ; Manica et al, ).…”

“…At the peak of the leap, males emit a high‐pitched song and return to the perched position to leap again a few seconds later (Manica, Macedo, Graves, & Podos, ). Previous studies have shown that the height of the leap is important for male pairing success (Carvalho et al, ; Manica et al, ). Given that avian predators can capture males during their leap display (R. Macedo, pers.…”

“…Nest predation is very high, with up to 80% of nests being depredated in some breeding seasons (Diniz et al, ). Predation is exacerbated because males continue to perform sexual displays during the nesting period within their typically extremely small territories (as small as 13.0 m 2 and average of 72 m 2 ; Almeida & Macedo, ; Carvalho et al, ). These displays apparently are excellent indicators of the location of male territories and nests, increasing nest predation risk (Dias et al, ).…”

“…This sexual display is emitted throughout the day and is more frequently performed when sunlight shines directly over the male's territory (Sicsú et al, ). Males maintain their sexual displays even after establishing a socially monogamous breeding pair (Macedo et al, ), probably to attract neighboring females to obtain extrapair copulations (Carvalho, Macedo, & Graves, ; Manica et al, ). Males perform these conspicuous displays despite having an active nest in their territories, and this has been shown to increase predation risk for nests (Dias, Castilho, & Macedo, ).…”

Social Environment Affects Acquisition and Color of Structural Nuptial Plumage in a Sexually Dimorphic Tropical Passerine

“…The nuptial plumage is exhibited during the sexual display, which consists of repeated, short vertical flights from perches at the periphery of the males' small territories [40], [42], [43]. Though socially monogamous, the high rate of extra-pair fertilizations [44], associated with the lek-like clustered territories [45], [46] highlight the importance of social interactions and the strong intra- and intersexual pressures that shaped this species' mating system [47]. Females nest within male territories, and both sexes feed the offspring [43].…”