DOI: 10.5061/dryad.s1rn8pk8k
title: Data for the Big Boom Theory: the Common Nighthawk wing-boom display delineates exclusive nesting territories

description: Understanding the functional significance of bird sounds can provide
 valuable insight into behavior and how birds use habitat. We show that the
 Common Nighthawk wing-boom display is a territorial signal associated with
 the nest location that can be used to identify territorial habitat use. In
 other words, the Common Nighthawk wing-boom display can be considered
 analogous to song due to its potential function in territoriality. We
 captured, tagged, and tracked 21 male Common Nighthawks in northeastern
 Alberta to confirm the functional significance of the wing-boom display
 and describe Common Nighthawk territoriality. Mean wing-boom use density
 (hereafter “area") size was 10.2 ha (SD=11.7 ha). We found minimal
 overlap in wing-boom area (5 of 15 neighboring male pairs, 0.2%-4.5%
 overlap), suggesting the wing-boom display represents an exclusive
 territory. Comparison of wing-boom locations and random points within the
 wing-boom area confirmed that male Common Nighthawks select areas near the
 nest to perform wing-boom displays. There was high wing-boom area overlap
 for the same individual between years. Differences between years reflected
 shifts in nest location, suggesting that the wing-boom display is a good
 indicator of the nest location and territory. Future Common Nighthawk
 surveys should record the type of acoustic signal observed to
 differentiate territorial and nesting habitat use. Many taxa that produce
 non-vocal sounds as part of breeding displays could similarly benefit from
 a functional classification of song to provide insight into habitat use.
description: Individual Tracking and Observation We
 captured and fitted male Common Nighthawks with VHF tags during the
 breeding seasons of 2016 and 2017. We used broadcast calls and a decoy to
 lure individuals into 38 mm mist nets. Individual males captured in 2016
 were selected based on presence at our five study sites. In 2017, we
 attempted to recapture the same individuals from the previous year, as
 well as additional males at the same study sites. Upon capture, each
 individual was fitted with either a 0.6 g PicoPip Ag376, 1.1 g Pip Ag392
 (Lotek wireless, Newmarket, ON, Canada), 0.35 g BD-2X, or 1.2 g BD-2
 (Holohil Systems Ltd., Carp, ON, Canada) VHF transmitter (0.4 – 1.7% body
 mass [mean=1.0% ± 0.5% SD]). All tags were attached to fall off naturally:
 BD-2X VHF tags were glued to the bare patch of skin between the feather
 tracts on the back with super glue gel (Gorilla Glue Company, Cincinnati,
 Ohio); Pip Ag 392 and BD-2 VHF transmitters were tied and glued to one of
 the central rectrices. All work was conducted under University of Alberta
 Animal Care and Use Approval AUP00001523. We relocated
 each individual throughout the breeding season and conducted observations
 of their acoustic behavior. We waited at least one day following capture
 to allow the birds to acclimate to the presence of the VHF tags. All
 observations were conducted between June 1 and July 20 when Common
 Nighthawks are nesting and between 21:30 and 03:30 when birds were active.
 Following relocation of the target individual, an observer conducted 10
 minutes of focal observation of the bird, marking the location of each
 wing-boom display on a datasheet with distance measurements. Focal
 observations were terminated early if the target individual was confused
 with other individual nighthawks. In a few instances, we also terminated
 the observation if the focal individual moved out of the observation area
 (&gt; 200 m); we assume those individuals were not leaving the area to
 wing-boom in other locations. Following each focal observation, the
 observer walked to the estimated location of each recorded wing-boom and
 used a GPS device to record the coordinates. Nest
 Location We attempted to locate the nest of each
 tracked nighthawk. Nightjar nests are cryptic and difficult to locate
 because incubating or brooding individuals will not flush until disturbed
 (Holyoak 2001). We thus relied on eyeshine to locate each nest; nightjar
 retinas have highly reflective <i>tapeta lucida </i>that
 reflects a yellow-orange luminescence. We searched each study site after
 dark by walking transects spaced approximately 100 m apart and sweeping
 back and forth with a high-powered headlamp. We assumed that the identity
 of the male for each nest was the male performing wing-boom displays
 around the nest area. On several occasions, we directly observed the male
 provisioning the chicks at that nest or interacting with the
 female.
description: All coordinates provided are in WGS84 decimal degrees. Nest
 locations in "ORNITH-21-054_NestLocations.csv" link to the
 wingboom locations in "ORNITH-21-054_WingboomLocations.csv" via
 the "BirdID" field.