Use of roadkill data to index and relate raccoon activity at a heavily predated, highdensity marine turtle nesting beach

Endangered Species Update, April-June, 2004 by Richard M. Engeman, Henry T. Smith, William J.B. Miller

Abstract

Four years of data from a high-density marine turtle nesting beach at John D. MacArthur Beach State Park, Florida were examined along with data on raccoon road-kills from adjacent roads, and data on park attendance (as an index of local traffic) to make inferences about raccoon activity patterns relative to turtle nesting. Raccoon road-kills were found to diminish substantially during turtle nesting, even though local traffic was constant or increasing. Opossums, the only other mammal consistently found as road-kills, did not show a decrease during turtle nesting season, but they are not known as a primary predator of turtle nests. We concluded that during turtle nesting raccoons are drawn to the beach to prey on the abundant food resource of turtle eggs, and they do not leave the beach until the end of turtle nesting season. High numbers of raccoon road-kills during the fall-winter, followed by a decrease in the spring around the start of turtle nesting season, might be used as indicators to initiate management actions to protect turtle nests.

Resumen

Cuatro anos de datos recolectados de una playa de anidamiento de alta densidad de tortugas marinas en John D. MacArthur Beach State Park, Florida fueron analizados conjuntamente con registros de mapaches atropellados en carreteras contiguas y datos de visitacion al parque (como un indicador del trafico local) para inferir patrones de actividad del mapache con relacion con el anidamiento de tortugas. Los mapaches atropellados se reducen sustancialmente durante la desova de tortugas, aunque el trafico local se mantuvo constante en aumento. La comadreja, el unico otro mamifero encontrado consistentemente atropellado, no mostro una reduccion en su poblacion durante la desova de tortugas, pero no son conocidos como un depredador primario de los nidos de tortugas. Hemos concluido que durante la epoca de la desova de tortugas, los mapaches son atraidos a la playa por la abundancia de huevos de tortugas y no dejan la playa hasta el final de la temporada de la desova de tortugas. Los numeros elevados de mapaches atropellados durante el otono-invierno, seguido por una reduccion en la primavera alrededor del comienzo de la temporada de la desova de tortugas, puede ser usado como un indicador para iniciar acciones de manejo para proteccion de los nidos de tortugas.

Introduction

Predation is a critical threat to many endangered or even locally rare species (Hecht and Nickerson 1999), and predation losses can have an increased deleterious impact due to the compounding effects of habitat loss and altered predator communities (Reynolds and Tapper 1996). In this regard, raccoons Procyon lotor cause substantial destruction of marine turtle nests in Florida and throughout the southeastern United States (Stancyk 1982); thus, they exemplify an abundant native vertebrate that negatively impacts the conservation of endangered species (e.g., Garrott et al. 1993). While urbanization and development of coastal Florida have reduced the beach areas where marine turtles successfully nest, raccoons have prospered in the face of urbanization. They flourish in close association with humans where their populations often receive artificial support through refuse or direct feeding (Dickman 1987; Dickman and Doncaster 1987; Riley et al. 1998; Smith and Engeman 2002). Increased availability and concentration of food, den sites or other refuges may induce dense populations of wildlife species that inhabit urban environments (e.g., Dickman 1987; Dickman and Doncaster 1987; Riley et al.1998), and raccoons have been observed to achieve extraordinary densities (up to 238/[km.sup.2]) in urban, coastal Florida (Smith and Engeman 2002). In addition, predators are known to recognize and key on high-density nesting areas (Lariviere and Messier 1998, Mroziak et al. 2000). Here, we examine four years of data from a high-density turtle nesting beach enclosed within an urban setting. We examine raccoon road-kill data from area roads during the same years to evaluate whether a raccoon migration to the high-density of nests is indicated.

Methods

Study site

John D. MacArthur Beach State Park (MBSP) is located on Singer Island in Palm Beach County, Florida, USA. It consists of 65 tidal wetland/submerged ha, and 71 upland ha for a combined total of 136 ha. Terrestrial plant communities consist of maritime hammock (49 ha) and beach dune (9.3 ha). MBSP is encapsulated within the City of North Palm Beach, and is surrounded by suburban infrastructure to the north and south. The property is bordered to the east by the Atlantic Ocean, and the Intracoastal Waterway (a large bulkheaded estuary) truncates the entire western boundary. State Road A1-A runs through MBSP parallel to the Intracoastal Waterway on the west side of Singer Island. This length of road is 2.6 km with a speed limit of 72 kph. The park also has another 1.1 km of infrastructure roads with a speed limit of 24 kph. No roads are immediately parallel to the beach on the Atlantic coast. Thus, wildlife from the beach would be unlikely to appear on the roads within a short time period.