Academic journal article The American Midland Naturalist

Nesting, Nest Predation and Hatchling Emergence of the Carolina Diamondback Terrapin, Malaclemys Terrapin Centrata, in Northeastern Florida

Academic journal article The American Midland Naturalist

Nesting, Nest Predation and Hatchling Emergence of the Carolina Diamondback Terrapin, Malaclemys Terrapin Centrata, in Northeastern Florida

Article excerpt

ABSTRACT.-

In 1997 and 2000 we monitored nesting by diamondback terrapins daily from 1 May through 31 October at a beach on an island in northeastern Florida. During our visits we recorded and marked newly oviposited intact nests, monitored previously marked nests for depredation, hatching or washout and identified nest predators. We recorded nest deposition from late April through late July, but most nests were found in June (2000) or July (1997). Most nests were depredated within 48 h of oviposition. Most depredated nests were found in June or July, and those from July included both newly deposited and recently hatched nests. Depredated nests in August and September were all recently hatched. The major nest predators were raccoons, but we also noted crows, boat-tailed grackles, armadillos, ghost crabs and two species of plant roots. Hatching and emergence began in early July and continued into October. The mean emergence period for 54 nests was 68.9 d. In 1997, 21.9% of marked nests were washed out by high tides or storms and 8.9% suffered that fate in 2000.

INTRODUCTION

Diamondback terrapins (Malaclemys terrapin) exist as seven subspecies inhabiting brackish water habitats from Massachusetts to Texas (Ernst et al., 1994). The Florida coastline with its saltmarshes, lagoons, bays, mangroves, islands and keys represents roughly one third of their range. Five subspecies live in Florida, but the only published studies of terrapins in the state concern M. t. tequestaoithe central Atlantic coast (Seigel, 1980a, b, c, 1983, 1984, 1993) and M. t. rhizophorarum in the Keys (Wood, 1992).

The northern subspecies, Malaclemys terrapin terrapin, exhibits 6 wk nesting seasons in June and July (Burger and Montevecchi, 1975; Lazell and Auger, 1981; Goodwin, 1994). Average incubation/emergence period is 10-11 wk, and hatching occurs from mid-August to mid-October. Raccoons are the major nest predators, and most nest depredations occur within 24 to 48 h of oviposition in the northern populations (Burger, 1977; Roosenburg, 1991; Goodwin, 1994). Seigel (1980c) found gravid Florida east coast terrapins on Merritt Island from late April through 1 July. However, nothing is known concerning natural incubation/ emergence times, nest predation or nest predators in the southern range.

Our research focused on Malaclemys terrapin centrata, the Carolina diamondback in northeastern Florida, which is intermediate in its geographic range and physical characteristics between M. t. terrapin and M. t. tequesta. The objectives of our study were to characterize nesting biology by measuring the following variables: (1) the length of and peaks in nesting activity, (2) the total number of nests present and how many survived to hatching, (3) the identity of nest and hatchling predators and peaks in predator activity and (4) the mean emergence period.

METHODS

Study area.-The terrapin nesting beach is on an island adjacent to the Intracoastal Waterway in Duval County, Florida. The island is roughly triangular with an area of approximately 100 ha. The 750 m long beach occupies the northeastern side of the triangle and ranges in width from about 10-25 in at high tide. Open sandy sections grade to higher areas with vegetation including saltgrass (Dislichilis spicata) and saltwort (Batis maritima). The area south of this narrow beach, representing over 90% of the the island, is typical saltmarsh, flooding often with spring tides, and with continuous stands of cordgrass (Sparlina allerniflora and S. patens).

Nests and season.-Once daily from 1 May through 31 October in both 1997 and 2000 two or three researchers walked up and back a 10 m wide corridor, roughly bisected by the high tide line, along the terrapin nesting beach and counted all intact and depredated nests. In most cases, terrapins left distinctive tracks to and from nests (crawls), and following crawls was the most reliable method we found for locating intact nests. …

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