Desley A. Whisson

Developing relative abundance techniques (RATs) for monitoring rodent populations

Accurate density estimates of rodents are frequently difficult or cost-prohibitive to determine. Thus, a number of techniques (track plates, monitoring blocks, chew cards/sticks, apple slice index, trapping) are often used to index rodent populations. Theoretically, the sensitivity of these indexing techniques could be improved if they applied continuous measurements rather than simple binary measurements (presence/absence). Development of a relative abundance technique that is simple to apply and sensitive to changes in population density is critical for the operational management of rodent pests. In addition to providing a quantitative measure of abundance with statistical parameters, an indexing technique that does not require handling of animals is important in consideration of potential disease issues (for example, hantavirus, arenavirus, etc.). We investigated track plates, chew cards and monitoring blocks and associated continuous measurement methods for calculating indices of rodent abundance. In laboratory and field settings, we tested their effectiveness in detecting different population densities of California meadow voles (Microtus californicus). Chew cards were poorly accepted by meadow voles in pen and field tests. However, track plates and monitoring blocks may provide useful tools for indexing meadow vole populations, and have application for other rodent species.

The effects of anthropogenic food on the spatial behaviour of small Indian mongooses ( Herpestes javanicus ) in a subtropical rainforest

The aim of this study was to determine the extent to which mongooses Herpestes javanicus in the Caribbean National Forest use areas of high human use, and to compare space use patterns in these areas to those in areas of low human use. It was expected that the abundance of anthropogenic food in areas of high human use would lead to (1) higher population densities; (2) smaller home ranges; (3) more extensive range overlap and reduced territorial behaviour, than areas of low use. During the dry season, 14 mongooses were radio-collared and tracked in each of two areas: an area of high human use and an area of low human use. Six of these mongooses, one in an area of low human use and five in an area of high human use, were also tracked during the wet season. In both seasons, mongooses in the area of high human use used picnic areas more than expected based on availability. In the dry season, mongooses in the area of high human use had smaller home ranges than those in the area of low human use. Ranges overlapped extensively in both areas, and slightly more so in the area of low human use. However, individuals avoided each other spatially within the shared area of their ranges, and core home ranges overlapped little. In the wet (breeding) season, home-range size and overlap increased more for males than for females. Such differences in behaviour and population dynamics in these two areas have implications for rabies transmission rates and management throughout the forest.

Home Range and Movements of Roof Rats (Rattus rattus) in an Old-Growth Riparian Forest, California

Abstract Information on the spatial ecology of nonnative roof rats (Rattus rattus) is important for developing management strategies to reduce their impacts on native wildlife in riparian habitats. We determined home-range size and movement patterns of nonnative roof rats (Rattus rattus) in an old-growth riparian forest in California by radiotracking 12 individuals in August and September 2002. Males had larger home ranges than females. There was considerable overlap of ranges within and between sexes. Rats nested from 2 to 15 m high in trees, and used multiple nests that were sometimes shared simultaneously with other rats. Rats were most active at night, spending most of their time on, or close to the ground, and favoring areas of dense cover of blackberry and grape.

Monitoring invasive mammalian predator populations sharing habitat with the Critically Endangered Puerto Rican parrot Amazona vittata

Critically Endangered Puerto Rican parrots Amazona vittata are one of the rarest birds in the world. Several exotic mammal species capable of preying on Puerto Rican parrots cohabit the Caribbean National Forest with the only wild population of these parrots. We used tracking plates, monitoring blocks and trapping to index black rats, small Indian mongooses and feral cats in parrot habitat and in public-use areas in the same habitat type. We had high trap success for black rats at all sites (42% of all sites combined), among the highest reported in the world. Rat response to monitoring (non- toxic bait) blocks was universally high, regardless of ground or tree placement. Mongooses were present at all sites, with a greater proportion of plates tracked within the forest than at public-use sites. Cats were present at all forest sites and one of the public-use sites. Presence of the three species did not appear to be linked to human disturbance. Because only 30-40 Puerto Rican parrots survive in the wild, with as few as three pairs nesting in 2002, we concluded that the abundance and pervasive- ness of exotic mammalian predators poses a greater threat to the parrots than has been generally acknowl- edged. This is evidenced by mammalian predation during recent parrot breeding seasons, including six fledglings taken by mongooses and one nest failure from rats during 2000-2003.

A visual method for indexing muskrat populations

Abstract The native range for muskrats ( Ondatra zibethicus ) includes much of North America, but they also have been introduced beyond their native range, including into the Fall River, California, where they have come into conflict with human interests. An easily applied method to assess their abundance is an important need for their management. We developed a muskrat visual index (MVI) to provide the information necessary to address this need. Observations were made at randomly located sites along the river. The number of muskrats observed during a 45 min period was recorded during the late afternoon peak activity time at each site on multiple days. The mean number observed over sites was calculated for each day. The index was the mean of the daily means. These design and measurement methods present valuable advantages over most traditional muskrat indexing methods in this environment. Traditional methods usually involve counting burrows or houses. However, in a relatively stable environment such as along the Fall River, muskat burrows and houses tend to be long-lasting structures, making acute changes in population difficult to detect by these methods. Examining these structures for activity can be time-consuming and labor-intensive. Of particular importance, the statistical properties inherent to the MVI data structure permit calculation of standard errors, confidence intervals and statistical tests allowing quantitative comparisons among MVI values. Development of a management program for muskrats on the Fall River will require understanding of muskrat population fluctuations and densities, as well as knowledge of the effectiveness (short- and long-term) of control strategies. Here we develop a useful method, derive its statistical properties, and present baseline information for managing muskrats along the Fall River.

Comparison of 0.005% and 0.01% diphacinone and chlorophacinone baits for controlling California ground squirrels (Spermophilus beecheyi)

Abstract.Diphacinone and chlorophacinone, first-generation anticoagulant rodenticides, are frequently used for control of California ground squirrels (Spermophilus beecheyi) in agricultural and rangeland areas in California, USA. Owing to growing concerns over the risks to non-target species associated with the use of these rodenticides, the USA Environmental Protection Agency (EPA) proposed that the concentration of baits for above-ground use should be reduced from 0.01% to 0.005% active ingredient. We conducted field trials to compare the efficacy of 0.005% and 0.01% chlorophacinone and diphacinone baits in broadcast and spot applications for control of California ground squirrels on rangeland. We found no significant difference in efficacy owing to bait type, concentration or application method. Repeat testing is needed in other habitat types (e.g. crop areas) where alternative foods might reduce the effectiveness of a 0.005% bait application.