DOI: 10.5061/dryad.7m0cfxq05
title: Abundance and occupancy of the western yellow-billed cuckoo (Coccyzus americanus) in Sonora, Mexico

description: Unveiling factors that determine abundance and distribution of endangered
 wildlife species has relevant implications in their conservation across
 international boundaries. For instance, the Western Distinct
 Population (as defined by the U.S. Fish and Wildlife Service) of the
 yellow-billed cuckoo Coccyzus americanus (Linnaeus,
 1758) has disappeared in most of the species’ range across the
 western United States and southwestern Canada, but little is known about
 the conservation status at the southern edge of its breeding distribution
 in Mexico. To fill this information gap, we estimated abundance and
 occupancy rates of yellow-billed cuckoos using a standard broadcast call
 survey protocol. We used Bayesian spatial count models to estimate cuckoo
 population density at survey sites. We used Bayesian hierarchical models
 to estimate the effects of geography, climate, and vegetation on occupancy
 rates while accounting for imperfect detection. Mean cuckoo count per
 transect for all sites was C = 9.00 ± 0.45
 cuckoos. Overall cuckoo density was D  = 13.18
 cuckoos/km2 (SD(D ) = 5.61 cuckoos/km2).
 Overall cuckoo occupancy in Sonora was φ = 0.538 (95%CrI(φ) =
 0.544–0.600) but showed strong geographic variation. Relatively high
 occupancy levels suggest yellow-billed cuckoo populations in Sonora may be
 robust, but they are largely reliant on declining high-tree cover.
description: We surveyed for cuckoos
 following the standard broadcast survey protocol for the species
 (Halterman et al. 2015) in the summers of 2015–2019 (5 years), but we
 reduced the number of surveys per sampling unit. We surveyed each site
 twice per year, with one survey occurring in each of the second and third
 standard survey periods. We reduced the number of visits per site to
 increase the number of sites surveyed. We conducted our first survey
 period from site from late June to late July and our second survey period
 from late July to no later than 16 August. For one upland site, we were
 denied access to conduct the second survey, and we instead surveyed the
 closest alternate upland site. We started the first survey period at the
 onset of the monsoon rains, which meant that at some sites, the rain
 effects of a greening vegetation were not always evident during the
 survey.  At each site, we surveyed for cuckoos using
 point counts placed on transects along the riparian gallery forest or
 desert arroyo vegetation, keeping as close to the river channel as
 possible. For upland sites, we used dirt roads, cattle tracks, or dry
 drainages. We began surveys just before sunrise and continued until 11:00,
 until temperatures reached 40°C, or until the surveyors identified potential
 human health risks, such as heatstroke or dehydration. The broadcast
 consisted of 5 contact/<em>kowlp</em> calls (70 db), each
 spaced one minute apart. We identified cuckoos by sight using size, form
 and plumage characteristics listed by Hughes (2020). We identified cuckoos
 by ear when we heard the
 contact/<em>kowlp</em> or <em>coo </em>call
 (Halterman et al. 2015), usually as a response of broadcasted
 contact/<em>kowlp</em> calls. Most cuckoo detections were from
 birds heard but never seen. We arrived at the broadcast-point and waited
 at least one minute to detect cuckoos. When we detected no cuckoos during
 the initial listening period, we began the first broadcast. When we
 detected no cuckoos at the broadcast-point after five broadcast calls, we
 continued 100 m along the transect and started a new broadcast as
 described above. After we detected an individual or a pair, we moved 300 m
 further along the transect before resuming the survey. When we encountered
 cuckoos between broadcast points (i.e., an unsolicited detection while
 traveling between broadcast points), we stopped and recorded all
 information in the same manner as if the detection had been made during a
 broadcast. Literature cited
 Halterman, M.,
 Johnson, M. J., Holmes, J.A., and Laymon, S.A. 2015. A Natural History
 Summary and Survey Protocol for the Western Distinct Population Segment of
 the yellow-billed cuckoo. U.S. Fish and Wildlife Techniques and Methods,
 45 p. Hughes, J. M. 2020. Yellow-billed
 cuckoo (<em>Coccyzus americanus</em>), version 1.0. In Birds
 of the World (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca,
 New York.
description: Notepad ++ (available at https://notepad-plus-plus.org).