Updated Distribution of the Lower Keys Marsh Rabbit

Abstract

The Lower Keys marsh rabbit (LKMR; Sylvilagus palustris hefneri) is endemic to the Lower Keys of Florida and exists as a metapopulation in patches of salt-marsh–buttonwood transition zone, freshwater wetlands, and coastal beach berm vegetation (Forys and Humphrey 1996). Local LKMR populations interact through dispersing individuals, and patches undergo periodic local extinctions and recolonization (Forys and Humphrey 1999a). Much of the LKMR’s habitat has been lost or fragmented by human development over the past several decades, prompting the United States Fish and Wildlife Service (USFWS) to list the subspecies as endangered in 1990 (USFWS 1990). Knowledge of the distribution of occupied and potential LKMR habitat patches is critical to the design of recovery strategies for the subspecies. Historically, LKMRs occupied most, if not all, larger islands from Big Pine Key to Boca Chica Key, and may have occurred on Key West as well (DePourtales 1877, Layne 1974, Howe 1988, Lazell 1989; D. Stevenson, Felix Environmental Services, personal communication; Fig. 1). Although rapid habitat loss occurred in the 1970s and 1980s (USFWS 1997), little information is available on the LKMR’s distribution prior to 1988. The oldest known written records are anonymous notes dated 1968–1987 written on blue line photographs discovered at the National Key Deer Refuge in 2003. These records documented presence of LKMRs at 20 sites on Big Pine Key. Howe (1988) conducted the first published survey of the LKMR metapopulation by surveying 13 patches noted by J. Lazell (The Conservation Agency, unpublished data) and 3 additional patches. He reported that rabbits were absent from 4 of these patches, no longer occurred on Cudjoe Key, and were threatened by human activities in remaining patches. Forys (1995) completed a more comprehensive survey from 1991 through 1993. She identified 59 patches of occupied and potential (i.e., unoccupied, but apparently suitable) LKMR habitat. This survey included all but 2 of the patches noted by Howe (1988). LKMRs consistently occupied 19 of these patches over the course of her study, occupied 23 other patches in 1 survey, and did not occupy 17 patches. In 1995, Forys et al. (1996) discovered an additional 19 and 47 occupied and potential patches, respectively. Forys (1995) and Forys et al. (1996) found no extant populations between Big Pine and Sugarloaf keys. Based on these surveys and demographic data collected by Forys (1995), a population viability analysis (PVA) model suggested the metapopulation had a 100% probability of extinction in the next 50 years (Forys and Humphrey 1999b). Researchers have not formally surveyed the range-wide status and distribution of the LKMR since the mid-1990s. Managers charged with the recovery of this species need current data. Therefore, we surveyed potential LKMR habitat throughout the Lower Keys from 2001 through 2005. Specifically, our objectives were 1) to update the distribution and occupancy status of LKMR habitat patches, 2) to document patterns in patch occupancy from 2001 through 2005, and 3) to draw comparisons to previous formal and informal surveys.