Nest Form, Colour and Nesting Habitat Affect Predation Rates of Australasian Warblers (Gerygone spp.) in Tropical Mangroves

Abstract

Abstract. Nest predation is high in mangals (mangrove communities) of the Australian monsoon tropics. The Large-billed Gerygone Gerygone magnirostris and Mangrove Gerygone G. levigaster are warbler-like birds that build domed nests, which are very di#erent from each other in size, form and colour. Large-billed Gerygone forages and builds nests along tidal creeks where vegetation is tall and dense, whereas Mangrove Gerygone primarily nests in shrubs around the edges of bare salt flats and forages in both habitats. Using artificial nests that mimicked those of the two species, we tested whether di#erences in nest appearance, including form and colour, were adaptations to avoid nest predation. Artificial Mangrove Gerygone nests in their main nesting habitat were predated less frequently than those on tidal creeks, whereas predation rates on artificial Large-billed Gerygone nests did not di#er between habitats. Our results suggest that Mangrove Gerygone nests are built in the primary breeding habitat to avoid nest predators. In addition, we identified a nest predator, the Yellow Oriole Oriolus flavocinctus.

Impact of brood parasitism and predation on nest survival of the fan‐tailed gerygone in New Caledonia

“…All these gerygone species build the same type of dome‐shaped nests and are parasitised by other species of bronze‐cuckoos (Payne ), which likely depredate host nests as well. As in our study, the main nest predators of Australian gerygone species, which build their nests in similar locations as the fan‐tailed gerygone, were native birds (Sato et al ). In general, the higher predation rates in gerygone species is consistent with the observed increase in nest predation rates towards the equator (Remeš et al ) resulting in higher nest predation rates in tropical species (Robinson et al , Roper et al ).…”

Nesting beside old nests, but not over water, increases current nest survival in a tropical mangrove-dwelling warbler

“…If such 'decoy' nests served to distract visuallyoriented nest predators, and induce them to stop searching, then one would expect 'predation' of artificial nests to be low, once such nests were found to be unproductive. Indeed, the 'predation' rate of artificial domed nests with plasticine eggs was lower than the predation rate of natural nests in Large-billed Gerygones (Sato et al 2010) and Superb Fairy-wrens Malurus cyaneus (Colombelli-Négrel and Kleindorfer 2009), although the difference may have been due to the absence of parental activity (Martin et al 2000) or other cues at artificial nests, as well as other factors (Colombelli-Négrel and Kleindorfer 2009).…”

“…The lack of support for this hypothesis may indicate that the major nest predators of this species are birds, which can easily access nests by flying to them, or mammals and reptiles that are adept swimmers. Indeed, in artificial nests mimicking those of the Large-billed Gerygone, Sato et al (2010) found that the marks left by 'predators' on plasticine eggs in almost all cases of 'depredation' were from birds. Moreover the only predation events witnessed on real nests of this species involved the Black Butcherbird Cracticus quoyi (Mulyani 2004;Sato et al 2010).…”

“…Indeed, in artificial nests mimicking those of the Large-billed Gerygone, Sato et al (2010) found that the marks left by 'predators' on plasticine eggs in almost all cases of 'depredation' were from birds. Moreover the only predation events witnessed on real nests of this species involved the Black Butcherbird Cracticus quoyi (Mulyani 2004;Sato et al 2010). The lack of observations or evidence of predation of Large-billed Gerygone nests by terrestrial animals (e.g., mammal faeces, severely damaged nests) casts further doubt on the aqua-phobic nest predator hypothesis, and suggests that factors other than nest predation are involved in nest site selection of this species.…”

“…Artificial nest studies in this region indicated that nest predation rates are significantly higher in mangals than in other local habitats (Noske et al 2008), and that within mangals, rates are higher in the tall mangrove forest along tidal creeks, which are regularly flooded at high tides, than in the short mangroves surrounding bare, infrequently inundated saltflats (Mulyani 2004;Sato et al 2010).…”