Influence of different sign-post designs on avian predator perching activity

Abstract

Beach-nesting shorebirds are declining due, in part, to human disturbance in nesting areas. Sign-posts are installed around nesting areas to protect nests from people, but they may serve as perches and attract avian predators. From March–August 2018, we used passive infrared game cameras to monitor perching activity on 15 variations of sign-post designs on 2 barrier islands in North Carolina. We observed 110 independent perching events dominated (70%) by common (Quiscalus quiscula) and boat-tailed grackles (Quiscalus major) and laughing gulls (25%; Leucophaeus atricilla). We compared how the number of days perching occurred was associated with sign shape, material, sign-construction (sign x shape), position on post, and presence/absence of a nail on top of the post. Position of the sign on the post had the strongest effect on the number of days perching events occurred (χ2 = 18.62 df = 2 P < 0.001). Signs positioned flush with the top of the post were most frequently perched on (10% of perching days), followed by signs positioned lower (5%) and higher (2%) than the post top. The frequency of avian predators perching on triangular signs (8%) and rectangular signs (5%) did not differ (X2 = 2.89 df = 1 P = 0.11). While sign material (metal: 12%; laminated cardboard: 11%; plastic: 13%) did not affect the probability of perching (χ2 = 1.06 df = 2 P = 0.58), triangular plastic signs (11%) had more (χ2 = 6.011 df = 2 P = 0.05) perching activity than rectangle-metal (6%) and rectangle-laminated signs (6%). Presence (3%) or absence (4%) of a nail on top of posts did not affect the number of days perching occurred on a sign-post (χ2 = 0.59 df = 1 P = 0.52). We recommend managers position signs high on the post to reduce occurrences of predatory perching. If a choice of sign shape and material is available, rectangular metal or laminated cardboard signs may also reduce perching activity.