A multiscale analysis of Gray Vireo (Vireo vicinior) nest-site selection in central New Mexico

Abstract

There are many gaps in our understanding of Gray Vireo (Vireo vicinior) life history especially as it relates to nesting ecology. Our objective was to determine habitat features selected by Gray Vireos for nesting to improve management strategies for breeding populations. We searched for Gray Vireo nests on Kirtland Air Force Base in Albuquerque, New Mexico from 2016 to 2017. We estimated Gray Vireo nest-site selection at the tree level, the surrounding vegetation, and at two broader scales corresponding to selection within territories. Nest-site selection was estimated for 99 Gray Vireo nests. For tree-level selection, we compared characteristics of nesting trees with mean characteristics from groups of six randomly selected one-seed junipers (Juniperus monosperma) within a 25m radius. We also compared overall vegetation characteristics at the 25-m scale for nesting plots and 66 randomly selected plots. Broadscale cover proportions of nest sites and random points were estimated at 50-and 100-m radius spatial scales using a geographic information system. Gray Vireos selected nesting trees that were taller and wider than other adjacent junipers. Selection of vegetation characteristics surrounding nests showed a similar pattern, where Gray Vireos nested in areas where junipers were taller, wider, and had greater foliage density than was randomly available. Broad-scale analyses suggested that Gray Vireos selected nest sites in areas with higher proportions of junipers at low elevations (< 1954 m), and lower proportions of junipers in higher elevations (> 1954 m); however, juniper proportions at nest sites consistently ranged from 15 to 30% of available cover. Gray Vireos also tended to select areas with less pinyon pine than what was randomly available at the 100-m radius scale. Future management strategies should provide large patches of old-growth juniper to optimize Gray Vireo nesting habitat. Analyse multiéchelle de la sélection du site de nidification du Viréo gris (Vireo vicinior) dans le centre du Nouveau-Mexique RÉSUMÉ. Notre compréhension du cycle biologique du Viréo gris (Vireo vicinior) est incomplète, particulièrement en ce qui a trait à l'écologie de nidification. Notre objectif était de déterminer les caractéristiques d'habitat recherchées par les Viréos gris durant la nidification afin d'améliorer les stratégies d'aménagement destinées aux populations nicheuses. Nous avons cherché des nids de viréos sur la base des forces aériennes de Kirtland à Albuquerque, au Nouveau-Mexique, en 2016 et 2017. Nous avons évalué la sélection des sites de nidification des viréos à l'échelle de l'arbre, de la végétation environnante et à deux autres échelles plus grandes à l'intérieur des territoires des oiseaux. Nous avons analysé la sélection du site de 99 nids de Viréos gris. En matière de sélection à l'échelle de l'arbre, nous avons comparé les caractéristiques des arbres abritant un nid avec les caractéristiques moyennes de groupes de six genévriers monospermes (Juniperus monosperma) tirés aléatoirement dans un ray...

Fine-scale plasticity in nest placement can compensate for poor quality junipers as nesting trees for gray vireos

“…Additionally, our data suggested that optimum juniper density for nest survival was 15–20% of the available cover; however, the confidence intervals for this relationship overlapped with zero. It is interesting to note, however, that this percentage of juniper cover is similar to optimum juniper density for gray vireo nest-site selection ( Harris, Smith & McMurry, 2020 ).…”

“…Elevations at random locations ranged from 1823–2148 m. Surveys were conducted at the same random points each year. At each point, we conducted a 10-min survey consisting of 4 min of passive surveying, followed by 1 min of broadcast of conspecific vocalizations from a portable speaker (Cass Creek Big Horn), followed by 5 min of passive surveying ( Harris, Smith & McMurry, 2020 ). Broadcasts were of an adult male Gray Vireo song from the Arizona Field Ornithologist Sound Library and were played at maximum volume.…”

“…Foliage density has been used as a proxy for nest concealment in other studies ( Banks & Martin, 2001 ; Borgmann & Conway, 2015 ). To estimate foliage density for many trees expediently, we used a modified Braun-Blanquet method ( Wikum & Shanholtzer, 1978 ; Harris, Smith & McMurry, 2020 ), where we estimated the percentage of limbs and trunks that were obscured by foliage at the side of the tree that the nest was located on and assigned a categorical value: 1 (0–25%), 2 (26–50%), 3 (51–75%), or 4 (76–100%). For measurements at the 25-m radius scale, we determined the mean tree height and width for trees within the plot, and counted the total number of junipers within this scale.…”

“…)-juniper ( Juniperus spp.) habitats, such as juniper savannas ( Harris, Smith & McMurry, 2020 ) and pinyon-juniper shrublands ( Schlossberg, 2006 ) throughout the species’ breeding range ( Barlow, Leckie & Baril, 2020 ). However, little is known about the species’ habitat requirements in pinyon-juniper habitats.…”

“…However, little is known about the species’ habitat requirements in pinyon-juniper habitats. In the southwestern United States, gray vireos often rely on junipers as a nesting substrate ( Harris, Smith & McMurry, 2020 ) and are more frequently found in areas with high proportions of juniper, lower proportions of pinyon pines, and greater shrub density ( Schlossberg, 2006 ). Consequently, gray vireo demography is likely dependent on the availability and quality of pinyon-juniper habitats.…”