RESEARCH AND MANAGEMENT OF BIRD DEPREDATIONS AT CATFISH FARMS

Depredations by fish-eating birds are a major constraint on production at commercial catfish facilities in the southeastern United States. A recent survey of catfish farmers estimated total losses due to direct predation by birds and costs associated with employing preventive measures at $17 million, or 4% of national sales. In 1988, the U.S. Department of Agriculture\u27s (USDA) National Wildlife Research Center (NWRC) established a research station in Mississippi to develop more effective methods for reducing the impact of birds on southeastern aquaculture farms. This paper describes the impact of double-crested cormorants (Phalacrocorax auritus, DCCO) on the catfish industry, describes control methods to reduce depredations by this species, and reviews some research currently being conducted at the NWRC Mississippi research station

Bait Stations for Controlling Voles in Apple Orchards

Bait stations made with polyvinylchloride (PVC) pipe were compared with hand-broadcast applications of rodenticides for achieving long-term control of pine and meadow vole populations (Microtus pinetorum and M. pennsylvanicus, respectively) in two apple orchards in the mid-Hudson Valley of New York. The stations were constructed of three pieces of 1.5-in diameter PVC tubing joined together in the shape of an inverted T . Roofing shingles were placed over the entrances to some of the bait stations to encourage use by voles, while others were left uncovered. All stations were tied to trees, with no attempt to place them near runways or burrow entrances. Both pine and meadow voles consumed bait from the stations, regardless of whether the entrances were covered with roofing shingles. However, plugging of entrances with dirt was prevalent during winter in stations with roofing shingles. Vole activity and capture success were consistently lower on the plots with the two types of bait stations than on either the control or broadcast baiting plots 13, 26, 39, and 52 wk posttreatment, although the differences were not statistically different (p \u3e 0.05). The best control was achieved during the winter and early spring. Although spoilage of bait due to high humidity may limit its effectiveness in Eastern New York during the late spring and summer, the inverted T bait station provides a practical means of controlling voles in apple orchards during winter and early spring

A Cost-Effective Method for Applying and Removing Bird-Exclusion Netting in Commercial Vineyards

Bird-exclusion netting can be highly effective for reducing bird damage to agricultural crops, but the high cost of materials and perceived difficulty of applying and removing it has discouraged many growers from using this technique. The expectation of extensive damage to a high-value crop may warrant the implementation of costly protection measures such as bird-exclusion netting. During 1987, we evaluated a method for applying and removing bird-exclusion netting in 4 commercial vineyards on the North Fork of Long Island, New York. The method involved altering a hydraulically-operated, front-end bucket-loader to accommodate loading and applying 5.2-m-wide nets directly over rows of grape vines. Applying the netting, including loading and unloading the rolls of netting, required an average of 2.5 hr/ha for 3 people. Removal required an average of 2.8 hr/ha for 3 people. The single largest cost was the price of the netting, which accounted for approximately 70-74% of the total cost of the program. Four growers have used the netting for 5 seasons with minimal damage and anticipate using the netting for at least 1 additional season. The total cost of modifying the tractor and purchasing, applying, and removing the netting, based on an estimated net life of 5 yr, was $509-$534/ha/yr. Assuming that the netting is 95% effective in preventing bird depredations, it provides cost-effective protection in vineyards where high levels of damage ( \u3e 6%) are anticipated. However, the netting may not be practical in small vineyards or where low levels of damage are expected. An increasing number of vineyard managers on Long Island are using bird-exclusion netting to protect their vineyards from birds

Comparison of Methods for Detecting Voles under Apple Trees

We conducted a study in 2 heavily infested orchards in the mid-Hudson Valley of New York to evaluate methods for detecting the presence of meadow voles (MV, Microtus pennsylvanicus) and pine voles (PV, M. pinetorum) under apple trees. We quantified several possible signs indicating the presence of voles in each of the 4 quadrants under the canopy of each tree, and then set and monitored traps until capture success in the orchard declined to zero. There was no evidence that the 4 quadrants differed with respect to any of the variables examined. The apple slice index (ASI) was the best indicator for both species. Detection improved significantly (P \u3c 0.05) when the ASI was used in conjunction with the number of runways (MV) or tunnels (PV) under the tree, although neither of the latter 2 signs was by itself a reliable indicator. The ASI and search for runways and tunnels should be conducted in at least 2 quadrants under each tree. The significance of these findings for managing voles in apple orchards is discussed

Evolving Bird Management Research at the USDA Wildlife Service\u27s National Wildlife Research Center

As the methods-development arm of the U.S. Department of Agriculture\u27s Wildlife Services program, the National Wildlife Research Center (NWRC) is charged with developing tools and information for protecting agriculture, human health and safety, and property from problems caused by wildlife, including birds. Increasingly the NWRC is being asked to provide basic ecological information on the population status of various bird species, and its role is expanding from a reactive one of providing management options to that of predicting long-term implications of various management actions. This paper describes several areas of research by NWRC scientists to address population-level questions in support of WS mission

Possible Effects of Catfish Exploitation on Overwinter Body Condition of Double-Crested Cormorants

Concurrent with the rapid growth of the Mississippi catfish industry during the 1980’s, there was evidence of similar growth of double-crested cormorant (Phalacrocorax auritus) populations wintering in the delta region of Mississippi. Observational and food habits studies indicate that this expansive industry, incorporating more than 100,000 acres of ponds, provides an enormous food base for overwintering populations estimated in recent years to exceed 50,000 birds. As much as 75 percent of the diet in certain roosting areas of the Mississippi delta consisted of catfish, and according to bioenergetic models cormorants can exploit as much as 940 metric tons of catfish per winter. Despite these data, there has been little attempt to demonstrate whether exploitation of this food base has increased body condition and possibly survival of wintering cormorants that return primarily to the Great Lakes region to breed. To examine this possible effect, we analyzed monthly changes in body masses of wintering cormorants collected in the delta region of Mississippi and compared premigratory body masses and fat deposition of Mississippi cormorants with those from areas without extensive aquaculture production. With the exception of adult females, all sex and age groups of cormorants collected in the delta during the winters of 1989– 90 and 1990–91 increased (P \u3c 0.05) their body mass from November to April. Over all months, body masses of adult males and adult females were greater than that of subadults. Standardized by wing chord length, the premigratory body masses of Mississippi males and females differed (P \u3c 0.0004) from premigratory males and females collected from Alabama in areas remote from catfish production. Premigratory fat deposition appeared to be responsible for the body mass increases, and omental fat mass was highly correlated (R = 0.721, P \u3c 0.0001) with body mass and also differed (P = 0.0003) between Mississippi and Alabama birds. We hypothesize that the improved body condition of cormorants resulting from exploiting catfish has increased their survival and contributed to the population explosion of cormorants observed over the past decade. We suggest additional studies to substantiate our findings and to clarify the importance of southern aquaculture on improving body condition and survival of cormorants

Possible Effects of Catfish Exploitation on Overwinter Body Condition of Double-Crested Cormorants

Concurrent with the rapid growth of the Mississippi catfish industry during the 1980’s, there was evidence of similar growth of double-crested cormorant (Phalacrocorax auritus) populations wintering in the delta region of Mississippi. Observational and food habits studies indicate that this expansive industry, incorporating more than 100,000 acres of ponds, provides an enormous food base for overwintering populations estimated in recent years to exceed 50,000 birds. As much as 75 percent of the diet in certain roosting areas of the Mississippi delta consisted of catfish, and according to bioenergetic models cormorants can exploit as much as 940 metric tons of catfish per winter. Despite these data, there has been little attempt to demonstrate whether exploitation of this food base has increased body condition and possibly survival of wintering cormorants that return primarily to the Great Lakes region to breed. To examine this possible effect, we analyzed monthly changes in body masses of wintering cormorants collected in the delta region of Mississippi and compared premigratory body masses and fat deposition of Mississippi cormorants with those from areas without extensive aquaculture production. With the exception of adult females, all sex and age groups of cormorants collected in the delta during the winters of 1989– 90 and 1990–91 increased (P \u3c 0.05) their body mass from November to April. Over all months, body masses of adult males and adult females were greater than that of subadults. Standardized by wing chord length, the premigratory body masses of Mississippi males and females differed (P \u3c 0.0004) from premigratory males and females collected from Alabama in areas remote from catfish production. Premigratory fat deposition appeared to be responsible for the body mass increases, and omental fat mass was highly correlated (R = 0.721, P \u3c 0.0001) with body mass and also differed (P = 0.0003) between Mississippi and Alabama birds. We hypothesize that the improved body condition of cormorants resulting from exploiting catfish has increased their survival and contributed to the population explosion of cormorants observed over the past decade. We suggest additional studies to substantiate our findings and to clarify the importance of southern aquaculture on improving body condition and survival of cormorants