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Project Work Plan

Department of Interior USGS GE PES
Fiscal Year 2014 Study Work Plan

Study Title: Understanding Greater Everglades mammal communities adjacent to and within the ARM Loxahatchee National Wildlife Refuge
Current Study Start Date: June 15, 2014 Current Study End Date: Sept. 30, 2014
Location (Subregions, Counties, Park, or Refuge): A.R.M. Loxahatchee National Wildlife Refuge and Management areas south of the refuge and north of I-75
Funding Source: GEPES
Funding History: none
FY14 USGS Funding:
Principal Investigator: Kristen Hart
USGS Project Officer: Kristen Hart
USGS Technical Officer: Scott Padgett
Supporting Organizations: University of Florida, USFWS, SFWMD, FWC

Overview & Objective(s):
The decline of mammal populations in Everglades National Park (ENP) over the last 20 years (Dorcas et al. 2012) is likely to have a profound influence on the ecology of the Everglades system and the likelihood of successful Everglades restoration. Published and unpublished accounts suggest that populations of mammals including white-tailed deer (Odocoileus virginianus), raccoon (Procyon lotor), opposums (Didelphis virginiana), round-tailed muskrat (Neofiber alleni), Everglades mink (Neovison vison evergladensis), and bobcat (Lynx rufus) have declined in ENP. There is mounting evidence that predation by the invasive Burmese python (Python molurus bivittatus) has contributed to these declines in the Greater Everglades Ecosystem (GEE). In a recently-completed project, we found that pythons were the dominant predator (77%) of released rabbits in ENP. Using marsh rabbits as a model, we found the probability of finding a marsh rabbit decreased to ≈ 0% with increased proximity to Flamingo, essentially "ground zero" for the python invasion. Yet, marsh rabbit occurrence was ≈ 100% in all wetland habitat types > 120 km from Flamingo. In addition to rabbits, little is known about the response of small mammals in the GEE that appear to make up a large proportion of python diet, with rice rats (Oryzomys palustris), in particular, accounting for 16% of the gut contains of pythons examined from 2003-2007 (M. Cherkiss, USGS, pers. comm.). Thus, it is likely that pythons are having a drastic impact on the small mammal communities in the GEE.

Loxahatchee National Wildlife Refuge (NWR), located in Palm Beach County, encompasses ≈ 60,000 ha of remnant wetlands in the northern portion of the GEE. The southern boundary of the refuge is approximately 150 km from Flamingo and no large constrictors have yet been detected there despite monitoring since 2009. As such, Loxahatchee may have mammal communities yet to be altered by pythons. Accordingly, there is an urgent need to rigorously quantify the mammal communities with Loxahatchee NWR and lands adjacent to the refuge on the southern boundary.

The specific objectives for this project are:

  1. Establish the baseline prevalence of mammals in areas within and adjacent to Loxahatchee NWR prior to the occurrence of pythons.
  2. Establish a long-term small mammal monitoring protocol to determine the population dynamics of small mammals within Loxahatchee NWR.

These objectives relate to overarching goals for which we are seeking additional funding in FY15:

  1. Compare the mammal communities within and adjacent to Loxahatchee NWR to data on mammal communities throughout the GEE
  2. Compare small mammal communities in Loxahatchee NWR to concurrent trapping effort on comparable habitats in the GEE.

Specific Relevance to Major Unanswered Questions and Information Needs Identified:
Regardless of the causes of mammal decline, it is clear that mammals play a critical role in the ecosystems as prey and predators of each other and other taxa (i.e., birds, invertebrates). They also play an important role in nutrient cycling and shaping vegetative communities through seed dispersal and herbivory.Thus, the unique Everglades ecosystem is likely being drastically altered by the lack of a functional mammalian community. Our effort constitutes the only current and rigorous effort dedicated towards understanding where and how mammal communities are changing throughout the GEE. To understand the implications of the loss of mammals throughout the system we must first understand how the system in being altered. The areas within and adjacent to Loxahatchee NWR provide one of the few remaining opportunities to understand that baseline mammal might have looked like prior to their recent declines.

Planned Products for FY14: See below (Task products)

Work Plan

Task Leaders: Kristen Hart
Phone: 954-236-1067
FAX: 954-475-4125
Task priority: High
Task Personnel: Robert McCleery (University of Florida)
Task Summary and Objective(s):


  1. Establish the baseline prevalence of mammals in areas within and adjacent to Loxahatchee NWR prior to the occurrence of pythons.
  2. Establish a long term small mammal monitoring protocol to determine the population dynamics of small mammals within Loxahatchee NWR.

To understand why and how mammal populations in the GEE are declining it is critical to understand the underlying dynamics that drive those populations. Rodents make up a large portion of the diet of pythons in the GEE, but unlike other many larger mammals in the system they still appear to be prevalent throughout the landscape. Nonetheless, it is likely that the survival and reproductive of mammals are drastically changed by pythons and that small mammal communities are driven by the sensitivity of each species to python predation. Loxahatchee NWR provides one of the only opportunities in the GEE to document and understand the dynamics of small mammals without the risk of python predation. This will allow us to have critical base-line data on small mammals that can be used to set management and conservation priorities for current python invasion. Furthermore we will combine the data from this project with data previously collected from comparably designed trapping effort on trees islands in Everglades National Park (ENP) and related research in Water Conservation Area 3A (funding from USGS Ecosystems Program). We will jointly analyze this data to determine if community composition, demographic rates and timing of recruitment of small mammals are changing in comparable habitats across the GEE.

Work to be undertaken during the proposal year and a description of the methods and procedures: All field data collection and sampling will occur from June 15 to August 30, 2014. Data will be processed and organized from August 30 to September 30, 2014.

We will survey 25 sampling plots within and adjacent to Loxahatchee NWR. We will stratify sampling plots by water depth and vegetation types. At each sampling point we establish a 30 x 30 m grid; within the grid, we will place 2 floating bucket traps with digital cameras inside. This design has been highly effective at detecting mink and small mammals in the Big Bend region of Florida (R. McCleery, pers. observ.) To digitally "capture" more of the terrestrial mammal species we will also place 2 additional cameras mounted at 40 cm high on trees or stakes on each plot. All cameras will be left at plots for 7 consecutive nights and each night will be counted as a separate survey. Additionally, we systematically survey each site twice for mammal scat and sign using belt transects. Finally, we sample plots for habitat structure including visual obstruction using a Robel pole (Robel et al. 1970), water depth (dm), and distance to water (m), distance to cover (m), and grass height (cm). If the water depth at the site does not allow us to place cameras at the site we will still survey for marsh rabbit and round-tailed muskrats and then survey to survey the closest suitable location with cameras.

To quantify the small mammal communities in Loxahatchee NWR we will identify 4 tree islands of greater than 600 m2 and establish long term small mammal trapping grids. Each site will be trapped every 4 months using standard small mammal mark and recapture procedures. We will also sample the vegetation on the islands and use digital trip cameras to quantify ambient predator communities. We will generate estimates of composition and survival and recruitment rates for each small mammal population. Additionally we will determine the influences of environmental characteristics with differing demographic rates.

Linked/related studies:
In February 2014, we began sampling 84 randomly placed sampling plots for mammals throughout the southern portion of GEE. This data is being collected using the same protocols we have proposed for the work in and around Loxahatchee. By combined these dataset we will examine the prevalence of mammals populations based a host of potentially synergistic factors inducing 1) python risk 2) hydrology 3) mercury concentrations 4) land cover type and 5) urban development. This will allow us to understand the patterns and stressors that are impacting mammal communities throughout the GEE and leading to unprecedented changes in the southern portion of the system. Additionally, we will use spatial modeling techniques to identity areas where we are seeing punctuated changes in mammal communities. For future research we will target these areas of punctuated change for intensive demographic studies and pilot management actions.

Specific Task Products:
We will have raw data on mammal occurrence, and we will determinerelative abundance of common mammals within and adjacent to Loxahatchee NWR. We will also derive initial estimates of community composition of small mammals on tree islands in Loxahatchee NWR.

Product: Summary Report   Delivery Date: October 1, 2014

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Last updated: 17 April, 2015 @ 09:25 AM (KP)