Mark E. Tobin

Laboratory Evaluation of Predator Odors for Eliciting an Avoidance Response in Roof Rats (Rattus rattus)

We evaluated eight synthetic predator odors and mongoose (Herpestes auropunctatus) feces for eliciting avoidance responses and/or reduced feeding by wild captured Hawaiian roof rats (Rattus rattus). In a bioassay arena, we recorded: (1) time until each rat entered the arena, (2) time elapsed until first eating bout, (3) time spent in each half of the arena, (4) number of eating bouts, and (5) consumption. Rats displayed a response to the predator odors in terms of increased elapsed time before initial arena entry and initial eating bout, a lower number of eating bouts, and less food consumption than in the respective control groups. The odor that produced the greatest differences in response relative to the control group was 3,3-dimethyl-1,2-dithiolane [from red fox (Vulpes vulpes) feces and mustelid anal scent gland]. Mongoose fecal odor produced different responses in four of the five variables measured while (E,Z)-2,4,5-trimethyl-Δ3-thiazoIine (red fox feces) and 4-mercapto-4-methylpentan-2-one (red fox urine and feces) odors were different from the control group in three of the five variables measured. These laboratory responses suggest that wild Hawaiian roof rats avoid predator odors.

Effects of trapping on rat populations and subsequent damage and yields of macadamia nuts

Abstract During the 1990–1991 and 1991–1992 crop cycles, the effects of snap trapping on rat populations in a macadamia orchard and subsequent damage and yields of nuts were evaluated. During 1990–1991, 1681 roof rats ( Rattus rattus ), 22 Polynesian rats ( R. exulans ), and one Norway rat ( R. norvegicus ) were captured; 360 rats of undetermined species were captured during 1991–1992. Cumulative rat damage for the entire season varied from 0.36 to 1.34% of total annual production in the trapped sections, and from 1.71 to 3.62% of total annual production in the reference sections. However, trapping had no effect on yields: the number of nuts, mass per nut and the total mass of undamaged nuts did not differ between the trapped and reference sections. The results suggest the need to examine crop yield more closely in assessing methods for managing rodent infestations in macadamia orchards. The commonly used indices based on rodent activity and proportion of nuts damaged may overestimate the impact of rodent depredations and exaggerate the effectiveness of control measures in macadamia orchards. A large incidental take of birds points to the need for more selective techniques before trapping is utilized as a damage control measure in Hawaiian macadamia orchards.

Field Testing Synthetic Predator Odors for Roof Rats (Rattus Rattus) in Hawaiian Macadamia Nut Orchards

Field trials were conducted to determine whether the synthetic predator odors 3,3-dimethyl-l,2-dithiolane (DMDIT) and (E,Z)-2,4,5-tri-methyl-Δ3-thiazoline (TMT) were effective at eliciting a behavioral response in wild roof rats (Rattus rattus). The study site was a Hawaiian macadamia nut (Macadamia integrifotia) orchard with a recent history of roof rat feeding damage. The synthetic predator odors were encapsulated in urethane devices secured to tree branches. Mark-recapture data from live-trapping of rats and radio telemetry location data were used to assess behavioral responses of rats to the predator odors. Mark–recapture data indicated that DMDIT and TMT had no effect on capture numbers, reproduction, or body weight of rats. There was some indication that distribution of captures and number of locations relative to treated trees in TMT areas were less than in controls, but this pattern was not significant. The predator odors had no effect on home range or median distance from center of activity (MDIS) of rats as measured by telemetry. There was a trend of increasing values of MDIS on TMT areas in session 1 but not session 2. Overall we could not detect significant differences or consistent trends in responses of rats to DMDIT or TMT in these field trials.

Nightly and Seasonal Movements of Boiga irregularis on Guam

Ass~~~c~.-Brown tree snakes (Boiga irregularis, BTS), inadvertently introduced to the island of Guam shortly after World War XI, have had catastrophic effects on the native fauna of this U.S. territory. We used radio-telemetry to monitor daytime refugia and nightly movements of 60 BTS (30 during each of two seasonal periods) to determine the extent of nightly, weekly, and monthly movements. Eighty-three percent of subadult daytime sightings were in trees, compared to only 49% of adutt daytime sightings. Most measures of movement did not vary with seasonal period, sex, or age class. BTS moved an average of 64 m (Range: 9-259 m) between successive daily refugia. Mean total cumulative distance traveled between successive locations from one afternoon to the next was 238 m during January-March and 182 m during MayJuly. However, over the course of each seasonal period (60-70 d), most snakes concentrated their activity within core areas. During each of the two seasonal periods, snakes were located a mean distance of only 78 m and 93 m, respectively, from their original release points 30-50 d after release. Sixty to 70 d after release, snakes were a mean distance of 92 m and 68 m, respectively, from their original release points. Snakes frequently crossed dirt roads that separated forested areas at the study site. They also utilized grassy and brushy clearings, but less than would be predicted by the occurrence of such clearings in the study area. These results suggest that under the conditions of this study, BTS would be slow to reinvade areas where snakes have been removed by trapping or other means.

Effects of simulated rat damage on yields of macadamia trees

Abstract Rattus rattus damages 5–10% of the developing macadamia ( Macadamia integrifolia ) nut crop each year, but the impact on yields of mature nuts has not been well documented. We evaluated the effects of simulated damage on yields of mature nuts at two locations on the island of Hawaii during the 1995 crop season. We removed 10 or 30% of the developing nut clusters from 5-year-old trees at 90, 120, or 150 days post-anthesis (dpa) and evaluated yields of mature nuts at 210–215 dpa. Removal of 10% of the crop load had no measurable effect on yields of mature nuts regardless of when damage was inflicted. Yields of trees with 30% of nut clusters removed differed from the control (no nut clusters removed) only when damage was inflicted at 150 dpa. These results raise questions about the cost-effectiveness of current rodent control programs, especially during early nut development. Growers may be able to tolerate damage to 10% of their developing nuts without suffering economic losses, and may be able to sustain losses as high as 30% provided that damage is incurred before 120 dpa. Damage control efforts should focus on reducing damage after 150 dpa. However, high rat populations and damage prior to 150 dpa might indicate the need to apply measures to reduce damage later in the crop cycle.

Double-crested Cormorant Movements in Relation to Aquaculture in Eastern Mississippi and Western Alabama

Abstract Concomitant with increasing numbers of the Double-crested Cormorant (Phalacrocorax auritus), catfish producers in eastern Mississippi and western Alabama have reported damage caused by cormorant predation. VHF telemetry was used to document movements of 25 cormorants from all known night roosts in the aquaculture producing areas of eastern Mississippi and western Alabama, January-April 1998. A total of 193 day locations and 396 night roost locations of the cormorants were obtained. Each cormorant was found in the study area for 57 ± 4 (SE) days. Each cormorant averaged three night roosts (range: 1-8) and spent 20 (±2) days at each night roost site. Over 95% of cormorant day locations were within 19 km of their night roosts. Catfish pond use by cormorants varied between roost sites. Cormorants from five of eleven night roosts had ≥30% of subsequent daytime locations on catfish ponds and birds from five of the six remaining night roosts did not visit catfish ponds on the following day. Foraging distance and frequency of night roost interchange was less for birds in this study than those reported from other aquaculture regions. We suggest roost harassment efforts should be focused on specific roost sites and some roost sites should serve as unharrassed refugia from which cormorants are less likely to cause damage to aquaculture.

Bait placement and acceptance by rats in macadamia orchards

Black rats (Rattus ruttus) cause extensive damage in Hawaiian macadamia (A4ucndamia integrifolia) orchards. Many growers apply rodenticides to reduce rat populations in orchards, but improper placement of bait may reduce the effectiveness of many baiting programs. We evaluated the optimum placement of bait in macadamia orchards among the three locations specified on current rodenticide labels. We placed a non-toxic oat bait treated with 0.75% tetracycline hydrochloride, an antibiotic that chelates with calcium in growing bones and teeth and fluoresces under UV light, in burrows, on the ground and in trees in separate orchard sections. We consistently captured the greatest percentage of marked rats (53-91%) in sections where we placed the bait in trees and the lowest percentage of marked rats (O-36%) where we broadcast bait on the ground. Placement of bait in burrows produced intermediate results (40-70%). These results suggest that broadcasting bait on the orchard floor reduces the effectiveness of rat control programs. Placing baits in trees targets rats that not only are most likely to eat the poison bait, but also are most likely to damage developing nuts. Published by Elsevier Science Ltd

Abundance and habitat relationships of rats in Hawaiian sugarcane fields.

A better understanding of factors that influence the distribution and abundance of 3 species of rats that occur in Hawaii and cause extensive damage to sugarcane fields should lead to more effective control strategies, such as species-specific use of rodenticides or habitat management that reduces pest populations. Thus, we estimated the relative abundances of the 3 species of rats at 4 Hawaiian sugarcane plantations that historically have received high levels of rodent damage, and quantified various environmental factors that might influence the distribution of these rodents. Overall, we captured 526 Norway rats (Rattus norvegicus), 335 Polynesian rats (R. exulans) and 139 blacks rats (R. rattus) during 11,200 trap-nights

Low Mitochondrial DNA Variation in Double-crested Cormorants in Eastern North America

Abstract Double-crested Cormorant (Phalacrocorax auritus) numbers are increasing throughout eastern North America. We compared variation for five portions of mtDNA to determine if genetic differences existed among portions of the breeding range that would need to be considered when formulating management programs. Sequences for four mtDNA regions were identical across sample locations; frequencies of two haplotypes of the mitochondrial Control Region were similar across sampling locations. There is no evidence of restricted gene flow among breeding areas, or between subspecies with different migratory patterns.

Microsatellite Variation of Double-Crested Cormorant Populations in Eastern North America

Double-crested cormorants (Phalacrocorax auritus) exhibit highly adaptive and opportunistic foraging behavior. This flexibility in foraging and increases in population size have led to conflicts with aquaculture and recreational and commercial fishing (Duffy 1995). Although double-crested cormorants roosting in the lower Mississippi Valley appear to have minimal negative impact on sport fisheries, they may have a significant impact on commercial aquaculture production in this region (Glahn and Brugger 1995, Glahn et al. 1998). In 2003, the U.S. Fish and Wildlife Service released the Final Environmental Impact Statement on doublecrested cormorant management allowing more flexibility in control of these birds in areas where they are negatively impacting aquaculture, habitat for nesting colonial waterbirds, and other public resources (U.S. Fish and Wildlife Service 2003). The U.S. Fish and Wildlife Service’s Final Rule expands the 1998 Public Resource Depredation Order (50 CFR 21.47) to permit control of double-crested cormorants at winter roost sites in the vicinity of aquaculture facilities. Populations of double-crested cormorants declined sharply in the 19th and early 20th centuries followed by several periods of population growth in the middle and later decades of the 20th century (Hatch 1995). Atlantic and Interior/Great Lakes migratory populations have seen the greatest increase in breeding pairs. Between the 1970s and 1990s, double-crested cormorant populations in the Atlantic increased 4-fold to more than 96,000 pairs (Hatch 1995). Although double-crested cormorants experienced a marked increase in population size from the 1970s to the 1990s, recent estimates suggest a reduction in the overall rate of growth (Tyson et al. 1999). Although most populations of double-crested cormorants are migratory, a resident population (P. auritus subsp. floridanus) estimated at 10,000–30,000 individuals occurs in Florida (Brugger 1995, Hatch 1995). Population estimates for Florida suggest stable resident populations of P. auritus subsp. floridanus with increasing numbers of wintering birds from migratory subpopulations (Brugger 1995). It is unclear whether or not the resident subspecies in Florida is a genetically distinct lineage, separate from migratory populations. If genetic differentiation is sufficient, it is possible that this resident population may warrant special consideration in management and any control efforts. In addition to the population in Florida, smaller colonies of nonmigratory birds have become established in other areas of the southeastern United States (e.g., Mississippi Delta, Reinhold et al. 1998; Louisiana, Hatch and Weseloh 1999). Determining genetic distinctiveness of diverse populations of double-crested cormorants and the extent of gene flow are important for regional management decisions (Hatch and Weseloh 1999). It is thought that individuals exhibit high fidelity to a colony site; although, no data exist to support this claim (Hatch and Weseloh 1999). Reduction of populations on breeding grounds might prove more feasible than reduction of wintering birds because double-crested cormorants nest in distinct colonies that can be readily accessed. Control efforts on breeding grounds would be most effective at reducing depredation if the natal areas of wintering birds can be identified. The number of band returns is insufficient to establish a relationship between double-crested cormorant nesting colonies in the northern United States and Canada and the wintering, depredating populations in the southeastern United States. Genetic markers have been used to associate wintering dunlin (Calidris alpina) and Canada geese (Branta canadensis) with breeding populations (Pierson et al. 2000, Wennerberg 2001). Sufficient genetic differentiation among breeding populations is necessary to correctly assign samples of wintering birds to their natal areas. An analysis of variation in mitochondrial DNA (mtDNA) found no evidence of genetic differences among migratory and nonmigratory populations (Waits et al. 2003). However, microsatellite loci are known to evolve rapidly and, thus, may reveal population structure even in the absence of mtDNA structure. For example, Goostrey et al. (1998) used highly polymorphic microsatellite markers to assess population structure and differentiation in European populations of great cormorants (P. carbo subsp. sinensis and P. carbo subsp. carbo). They detected high levels of variation both within and among populations suggesting the potential for detecting differences among populations of double-crested cormorants. Our primary objectives are to 1) characterize the genetic 1 E-mail: claygreen@txstate.edu 2 Present address: Department of Biology, Texas State University, San Marcos, TX 78666, USA 3 Present address: Department of Biology, University of Memphis, Memphis, TN 38152, USA