The relationships of breeding stage to daytime singing behaviour and song perch height in Bermuda White-eyed Vireos (Vireo griseus bermudianus)

Abstract

Bird song is crucial for attracting mates and defending territories, but different types of song or different singing behaviours may be involved in acquiring or maintaining each resource. Furthermore, male songbirds may adjust when and where they sing throughout the breeding season, depending on their breeding stage. However, such relationships remain untested in several avian taxa. Here, we studied male Bermuda White-eyed Vireos (Vireo griseus bermudianus), a passerine with two distinct song types (discrete and rambling), to test the mate attraction, territory defence, and nesting stage hypotheses. We compare song rate and song perch height among different stages of the breeding season and during the non-breeding season. We show that male vireos produce both song types during the breeding and non-breeding seasons, suggesting dual roles in mate choice and territorial defence. Singing rate did not differ between the two seasons, but, within the breeding season, males without nesting duties had significantly higher song rates than males with nesting duties. Song rate was lowest during the nestling stage, which coincided with the highest rate of nest predation. Song perch height was higher during the breeding season versus non-breeding season, among males without nesting duties compared to males with nesting duties, and when males produced discrete versus rambling songs. Our findings suggest that male vireos increase their conspicuousness to prospecting females by increasing singing rate and song perch height, and that they sing during the breeding and non-breeding seasons to defend year-round territories. Collectively, our study supports the mate attraction and territory defence hypotheses of bird song and suggests that Bermuda White-eyed Vireos adjust their singing rate in response to nest predation risk.

The relationships of breeding stage to daytime singing behaviour and song perch height in Bermuda white‐eyed vireos Vireo griseus bermudianus

“…robins Petroica australis, and chipping sparrows (James 1978, Powlesland 1983, Liu and Kroodsma 2007); these researchers suggest that singing from elevated perches increases an unmated male's visual and acoustic conspicuousness to prospecting females. Field observations of Bermuda vireos (Mejías 2021) provide further support that singing from elevated perches is a mechanism for attracting prospective females: 1) breeding pairs travel primarily in the understory, 2) nests are never built in the canopy, but, rather, from forked branches, usually 2-3 m above the ground, and 3) males often return to canopy perches after their mate disappears, typically following nest failure. The tendency of males to select higher perches when singing discrete song versus rambling song might be because discrete song is described subjectively as being louder than rambling song (Bradley 1980); the combination of being louder and being sung from higher perches may reflect a history of selection for maximizing signal transmission distance (Sprau et al 2012, Podos andSung 2020).…”

“…Sunshine and light winds occur from April-September, whereas rain and gales are more prevalent during the winter months (Amos 1991). Present-day wooded habitat in Bermuda is dominated by invasive secondary forest (Mejías andNol 2020, Mejías and. Amongst our two study sites, Spittal Pond Nature Reserve (24 ha) and Ferry Reach Park (26 ha) (Fig.…”

“…Whenever possible, we identified and reported the causes of nest failure, for descriptive purposes. The black rat Rattus rattus, great kiskadee Pitangus sulphuratus, and Argentine ant Linepithema humile were abundant across study sites and are known predators of Bermuda vireo eggs and chicks (Mejías 2021). Predation from ants was obvious because swarms would usually take several days to consume eggs and nestlings.…”

“…Data are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.47d7wm3k0 (Mejías and Wilson 2023).…”

“…A non-migratory subspecies known as the Bermuda white-eyed vireo V. g. bermudianus or 'chick-ofthe-village' (hereafter Bermuda vireo) is an endemic breeder on the Bermuda archipelago (Bangs andBradlee 1901, Mejías et al 2021). It rears one brood per season, although pairs can make up to five breeding attempts per year following nest failure (Mejías 2021). Like its continental counterpart, only males sing discrete and rambling songs (M. Mejías pers.…”