Recording effort and a general description of singing behaviour
Bermuda Vireos were vocally
conspicuous amongst the island’s woodland avifauna. Counter-singing
among neighbouring males was common and we observed this at both the
edge and interior of a singer’s territory. Our fieldwork produced 430
15-min recordings across the breeding (April 2019–August 2019; N= 374 recordings) and non-breeding seasons (December 2019–January 2020;
56 recordings), equating to 6,450 min. We obtained more recordings of
focal males during the breeding season (mean ± SD: 31 ± 3 recordings per
male; range: 26–37 recordings; N = 12 males) than the
non-breeding season (5 ± 0.30 recordings; 5–6 recordings; 11 males)
because our winter residency on the island was limited compared to the
summer months, and because the breeding season was subdivided into five
stages. Subjects produced at least one song in 349 (81%) of the 430
recordings. A total of 17,682 vireo songs were detected from the
recordings, and, of these, 16,818 (95%) were discrete songs and 864
(5%) were rambling songs. Males produced both song types during the
breeding and non-breeding seasons; discrete song rate was fairly
constant throughout the breeding and non-breeding season, with the
lowest rates recorded in August (Figure 3). We noted that August also
marked the onset of feather moult in our subjects, where males with
missing tail feathers spent more time feeding quietly than singing.
Male Bermuda Vireos used multiple song perches throughout their
territories and vocalized at varying distances from their nests. Seldom
did males vocalize while either sitting inside the nest cup or while
perched on the rim. Occasionally, incubating males sang a couple of
discrete songs, with noticeably longer pauses between songs. These were
often followed immediately by the female returning to the nest and
relieving the male, which then resumed steady bouts of discrete song
away from the nest. In general, breeding males used song perches away
from the nest (mean ± SD: 18 ± 18 m; range: 0–86 m). With respect to
perch height, males accompanied by a female or engaged in nesting duties
often alternated between singing and flutter-hopping amongst understory
perches. In contrast, males in the breeding season with no nesting
duties usually performed stationary song bouts from exposed canopy
perches.