No place to nest or bask: Effects of human disturbance on the nesting and basking habits of yellow-blotched map turtles (Graptemys flavimaculata)
Introduction
Although habitat destruction or modification and the introduction of invasive species are generally considered to be among the most important threats to biodiversity (Foin et al., 1998), considerable attention recently has focused on the ways in which human disturbance alters the behaviour of imperiled taxa (see review in Frid and Dill, 2002) and whether such alteration leads to reduced population sizes (Gill et al., 1996, Beale and Monaghan, 2004). Studies on organisms as diverse as waterfowl (Gill et al., 1996, Rodgers and Schwikert, 2002), marine mammals (Constantine et al., 2004, King and Heinen, 2004), and large terrestrial game species (Stockwell et al., 1991) indicated that human disturbance can significantly alter feeding schedules, habitat use, and time spent nursing young. Even though the population consequences of such disturbances often are not known, changes in behaviour and habitat use concern conservation biologists and wildlife managers.
Despite the wealth of information available for birds and mammals, comparatively little is known about how human disturbances affect reptiles, perhaps because most reptiles are secretive and are not commonly seen by the public (but see Johnson et al., 1996, Hecnar and M.’Closkey, 1988, Parent and Weatherhead, 2000). However, in many aquatic habitats, freshwater turtles are frequently seen basking and nesting, especially in river systems where human recreational activities are common. Direct harassment of basking turtles by recreational shooters (“plinking turtles”) is a well-known activity in much of North America (Ernst et al., 1994) and has obvious negative impacts. The ways by which less overt disturbances affect aquatic turtles is poorly known, but given the rapid decline seen in many turtle species throughout the world (Gibbons et al., 2000), data on such impacts clearly are needed.
From 1993 to 1997, we studied the behavioural and reproductive ecology of the yellow-blotched map turtle (Graptemys flavimaculata) on the Pascagoula River in southeastern Mississippi, USA. This turtle underwent a severe decline in the 1980s and is currently listed as Threatened under the US Endangered Species Act of 1973, as amended. One of the major factors contributing to this decline is human disturbance, especially on sandbars where this species nests (U.S. Fish and Wildlife Service, 1991). Here, we report information on nesting and basking behaviour in this species, specifically on the impacts resulting from human disturbance. Further, we make recommendations to area managers as to how these impacts could be minimized.
Section snippets
Methods
Our research was conducted within the Ward Bayou Wildlife Management Area in a small portion of the Pascagoula River near Vancleave, Jackson County, Mississippi (Fig. 1). Two boat landings, located 5.0 km upstream and 10.6 km downstream of the study site, function as a source for human activity. We studied a 300 m section of the river, which included both a nesting beach (Beach #7) on the west bank and a basking area along the east bank (Fig. 1). The nesting beach was a sandbar approximately 50 m
Nesting behaviour and timing of nesting
We logged >270 h of observations of turtle nesting behaviour during 1997 and 1998. All nesting attempts occurred between 06:11 and 16:49 h, with a peak number of occurrences (48%) between 15:00 and 17:00 h (Fig. 2). Of 15 females seen to nest successfully, we had an unobstructed view of 10 (eight from 1997 and two from 1998), and we documented the details and duration of each nesting event. Females waited in the water “watching” the beach prior to nesting for lengthy periods of over six and a half
Effects of human disturbance on nesting behaviour
As is true of waterfowl and some marine mammals, we found that the behaviours of yellow blotched map turtles were altered by human recreational activities. Turtles attempting to nest commonly abandoned their attempts upon the approach of a boat. Prior to nesting, numerous individuals waited several hours near the sandbar without emerging to nest. Because of perceived threats or disturbances, females had less than a 19% chance of successfully completing oviposition once they emerged onto the
Acknowledgements
We are most grateful to R. Jones for inviting us to participate in this project and for lending us his expertise on map turtles, Funding was provided by the US Army Corps of Engineers, the US Fish & Wildlife Service, and the Mississippi Department of Wildlife, Fisheries, and Parks, and we thank R. Jones, L. LaClaire, and B. Peck for their support. Additional funding and support was provided by the Department of Biological Sciences of Southeastern Louisiana University, especially G. Childers and
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Present address: Minnesota Department of Natural Resources, 1801 South Oak Street, Lake City, MN 55041, USA.