DOI: 10.5061/dryad.47d7wm3k0
title: Data for: The relationships of breeding stage to daytime singing behaviour and song perch height in Bermuda White-eyed Vireos (Vireo griseus bermudianus)

description: 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 and territory defence
 hypotheses. We compare song production 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. Song production did not differ significantly
 between the breeding and non-breeding seasons, but, within the breeding
 season, males without nesting duties sang significantly more songs than
 males with nesting duties. 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 song
 production 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.
description: We audio-recorded the daytime
 (0700–1200 h) singing behaviour of 12 marked male birds throughout most of
 the subspecies' breeding season (April 2019 – August 2019). Of these
 12 males, we found and re-recorded 11 during the following non-breeding
 season (December 2019 – January 2020). As part of our sampling regime, we
 visited one of our two sites each day during favorable weather (i.e., no
 rain and little to no wind), alternating between sites each day. In total,
 we visited the Ferry Reach Park site 41 times during the breeding season
 and 5 times during the nonbreeding season. We visited the Spittal Pond
 site 44 times during the breeding season and 7 times during the
 nonbreeding season. While at a site, we recorded each male at the site in
 a random order during a separate 15-minute recording session throughout
 the morning. Upon arriving at a subject's territory, we
 searched for him for ≤ 15 min. If we found him, we waited 2 min before
 commencing recording. If we did not see or hear the focal male after 15
 min, we stood in the approximate center of his territory, waited an
 additional 2 min, and commenced recording. If a vireo began singing from
 what we thought was the inside of his territory, we immediately approached
 him while recording. If we located the singing male and confirmed that he
 was our focal subject, we included in our analysis all the songs recorded
 throughout the 15-min session, including those acquired before visually
 locating him. In the rare instances when the singing male we located was
 not the focal subject (e.g., a neighbour), we aborted the recording
 session and repeated it later that day.
 We recorded subjects
 throughout their 15-min session with a digital audio recorder (Marantz
 PMD661 MK II Professional recorder; WAVE format; 44.1 kHz; 16 bits) and a
 shotgun microphone (Sennheiser ME66 with K6 power module; super cardioid
 pickup pattern; 40-20,000 Hz frequency response (± 2.5 dB)) fitted with a
 foam windscreen. Recordings were made by following the subject no closer
 than 5 m while pointing the microphone directly at him (or towards the
 source of the songs if we had not yet located him). For each song produced
 while the subject was visible, we spoke into the microphone and visually
 estimated his song perch height above the ground (estimated accuracy ± 1
 m); very few trees across Bermuda Vireo territories were &gt; 10 m;
 all height estimates were made by the same person. We noted any periods in
 which we lost visual contact with the subject, but always continued
 recording until the 15-min session expired.
 During the breeding season
 (April 2019 – August 2019), we revisited subjects in the afternoons
 (1300–1700 h) to document their breeding activities. We spent a maximum of
 30 min searching for a given male and usually found them on account of
 their loud vocalizations and small territories. We followed located males
 at a minimum distance of 5 m and categorized them into one of six breeding
 stages: (1) no nesting duties, (2) nest building, (3) egg stage, (4)
 nestling care, (5) fledgling care, or (6) non-breeding (non-breeding
 status was assumed for all males between December 2019 and January 2020).
 We defined nest building as the stage when vireos are adding materials to
 a nesting branch until a nest is completed. We defined the egg stage as
 the period after nest completion, when the vireos are engaged in egg
 laying and incubation; the egg stage terminates at hatching. Nestling care
 is the stage when nestlings are seen inside the nest cup and the parents
 are actively feeding or brooding them. Fledgling care is the stage when
 the young are outside the nest and being fed by their parents. During the
 breeding season, we considered males to have nesting duties if they were
 engaged in nest building, the egg stage, nestling care, or fledgling
 feeding, and to be without nesting duties if they were not engaged in any
 of the above nesting behaviours with a female.
 We generated a waveform and
 spectrogram (Hamming window, FFT = 512 samples, 87.5% overlap) for all
 15-min recordings using Raven Pro sound analysis software (v1.5; Cornell
 Laboratory of Ornithology, Ithaca, NY). On each spectrogram, we drew
 cursor boxes (hereafter, “annotated”) around vireo songs that were visible
 on the spectrogram and waveform (i.e., clear pulses in amplitude). In some
 instances, songs from non-focal males could be seen and heard in the
 background of the recording, but these were easily distinguished from the
 subject's songs either because they were relatively faint or because
 they did not match the known vocal repertoire of the subject.
 We defined songs as
 vocalizations comprising one or more elements, where elements of the same
 song are separated by &lt; 0.5 s and those of different songs are
 separated by ≥ 0.5 s.
description: The R language and environment for statistical computing and
 graphics.