Reproductive Seasonality of Seven Neotropical Passerine Species

Abstract

Abstract. We investigated gonad sizes, nesting patterns, and plasma hormone concentrations of seven Neotropical passerine species in a lowland tropical rainforest (Panama) at 9ЊN latitude over at least one annual cycle. All species had entirely regressed gonads for several months of the year (October to January), coinciding with the end of heavy rainfall. Gonadal recrudescence started in the dry season between January and March. Nesting began earlier (March) for open-habitat species than for forest-interior species (April), and lasted until August or December, respectively. Species differed widely in maximal relative testes sizes and reproductive hormone concentrations, but both measures were lower than in most temperate-zone species. Although we cannot provide a phylogenetically controlled comparison, polygynous and group-living species appeared to have larger testes than monogamous species, possibly indicating sperm competition. Testosterone concentrations were highest in polygynous species, intermediate in socially monogamous species, and lowest in a groupliving species, indicating that testosterone is more influenced by social systems than by gonad cycles. Tropical birds may generally maintain low testosterone concentrations and relatively small gonads to decrease overall energy expenditure compared to temperate-zone relatives.Key words: breeding season, gonad cycles, hormones, Panama, rainforest, seasonality, tropical. Estacionalidad Reproductiva de Siete Especies Passeriformes NeotropicalesResumen. Investigamos los tamaños de las gónadas, los patrones de nidificación y las concentraciones hormonales plasmáticas de siete especies de aves paserinas Neotropicales en una selva lluviosa tropical de tierras bajas en Panamá (9ЊN) durante por lo menos un ciclo anual. Todas las especies tenían gónadas enteramente retraídas por varios meses del año (octubre a enero), coincidiendo con el fin del periodo de precipitación lluviosa pesada. El crecimiento gonadal comenzó en la estación seca, entre enero y marzo. La nidificación comenzó primero en las especies de hábitat abierto (marzo) que en las especies de interior de bosque (abril) y duró hasta agosto y diciembre, respectivamente. Las especies difirieron extensamente en los tamaños relativos máximos de las gónadas y en las concentraciones de la hormona reproductiva, aunque ambas medidas fueron menores que para la mayoría de las especies de la zona templada. Aunque no podemos proveer una comparación controlada por filogenia, las especies poliginias y las especies que viven en grupo tenían testículos más grandes que las especies monógamas, lo que posiblemente podría estar indicando competencia espermática. Las concentraciones de testosterona fueron mayores en las especies poliginias, intermedias en las socialmente monógamas, y menores en las especies que viven en grupo, indicando que la testosterona estaría más influenciada por el sistema social que por los ciclos de las gónadas. Las aves tropicales podrían generalmente mantener niveles bajos de testosterona y tamaños r...

Androgen and the elaborate courtship behavior of a tropical lekking bird

“…In the few lekking species that have been studied, males have high levels of androgen as long as they are actively displaying on their leks (Alatalo et al, 1996;Lisano and Kennamer, 1977). In general, tropical birds differ from their temperate-breeding counterparts by having relatively low levels of circulating T throughout the reproductive season (Goymann et al, 2004;Gwinner and Scheuerlein, 1999;Hau et al, 2000;Levin and Wingfield, 1992;Wikelski et al, 2003). This is particularly the case of species that, like the golden-collared manakin, live at low altitudes and have a long breeding season (Goymann et al, 2004).…”

“…T decreases afterwards, probably because elevated T concentrations are costly in terms of parental care (reviewed in Wingfield et al, 2001) and immunocompetence (Folstad and Karter, 1992). By contrast, males of many tropical species with prolonged breeding seasons typically have low levels of plasma T (reviewed by Goymann et al, 2004;Levin and Wingfield, 1992;Wikelski et al, 2003), unless they live at high elevations (Moore et al, 2002). However, high levels of T have been found in some tropical species during courtship (Chastel et al, 2005;Levin and Wingfield, 1992;Wiley and Goldizen, 2003).…”

“…In the few lekking species of temperate regions that have been studied, males have high levels of androgen as long as they are actively displaying on their leks (Alatalo et al, 1996;Lisano and Kennamer, 1977). A recent study reported that in manakins T is elevated in males during parts, but not all, of the long breeding season (Wikelski et al, 2003), although the courtship activity of the individuals was not recorded.…”

Testosterone and its effects on courtship in golden-collared manakins (Manacus vitellinus): Seasonal, sex, and age differences

“…In comparison to temperate breeding species, T levels of tropical male birds are generally lower year round and breeding seasons are longer (Dittami, 1986, 1987, Dittami and Gwinner, 1990Wikelski et al, 2003). Although some degree of seasonality in reproduction appears to be the rule (Dittami, 1986(Dittami, , 1987Dittami and Gwinner, 1990;Wikelski et al, 2003), there appears to be little association between T levels and territoriality (Fedy and Stutchbury, 2006;Wikelski et al, 2003). Some species are highly territorial year round despite low T levels and other species have variable T levels with consistent levels of territoriality (Wikelski et al, 2003).…”

“…Males of these species show discrete seasonally in both T levels and reproduction and a direct link has been shown between T and the activation of display behaviors (Balthazart, 1983;Silver and Ball, 1989;. Several recent studies have examined birds breeding in the tropics to see if, like their temperate breeding counterparts, T is elevated during the breeding season to activate reproductive and aggressive behaviors (Dittami, 1986(Dittami, , 1987Fedy and Stutchbury, 2006;Goymann et al, 2004;Hau et al, 2000;Moore et al, 2004a,b;Wikelski et al, 1999Wikelski et al, , 2003.…”