Effects of Aldrin Exposure on Snow Geese in Texas Rice Fields

In 1972 and 1974, 112 dead or moribund snow geese (Chen c. caerulescens), mostly immature white-phase males, were found in a study area on the Garwood Prairie, Texas. Dying geese were observed within 2 days after rice fields planted with aldrin-treated seed were flooded by heavy rains on 21 March 1972 and 25 March 1974. Brains from 8 snow geese that were moribund when found contained an average of 8.2 ppm (4.9-14.0 ppm) of dieldrin (a metabolite of aldrin); brains of 14 geese found dead contained an average of 14.1 ppm (2.1-31 ppm). Because no mortalities occurred in 1973 when aldrin-treated rice seed was flooded after all geese had migrated or in 1975 and 1976 after the treatment of rice seed with aldrin was suspended, it appears certain that aldrin caused the mortalities. J. WILDL. MANAGE. 43(1):94-101 During the spring of 1971, many geese died on the winter range in southeast Texas in areas where aldrin-treated rice seed was planted in early March and flooded in late March. More than 300 dead geese were counted in ground and aerial surveys in a 5-county area of the Texas rice-growing region; at least 180 of these were at reservoirs and in rice fields on the Garwood Prairie. Goose mortality had been reported in this area in earlier years, and detailed investigations were undertaken in 197276. Circumstances under which goose losses occurred in these years, symptoms of dieldrin poisoning in moribund geese, and quantities of dieldrin and mercury residues in brains of dead or moribund geese are described. I thank L. Krenek and R. Korenek, rice growers on the Garwood Prairie; and H. Baer (veterinarian), L. Blus, and G. Heinz (biologists), U.S. Fish and Wildlife Service, for review of the manuscript. STUDY AREA CONDITIONS The 11.3 x 4.8-km study area is on the Garwood Prairie, Colorado County, Texas, 4.8 km southwest of the town of Garwood about 100 km inland from the Gulf of Mexico. The land use consisted largely or rice fields and pastures, interspersed wi h woodland, and included 2 large reservoirs (about 4 km apart) and many small ponds. Rice was planted in March or April of each year at about 112 kg/ha (100 lb/acre). Nearly all seed planted in 1972, 1973, and 1974 was treated with aldrin at 2.5 g/kg of seed (4 oz/100 lb). In October 1974, the U.S. Environmental Protection Agency suspended aldrin as a rice seed treatment; consequently, no aldrin-treated seed was planted in 1975 and 1976. Purpose of the treatments was to control rice water weevil (Lissorhoptrus oryzophilus) larvae. However, larvae in Texas had shown increased resistance to aldrin since 1964 (Bowling 1968, 1972). Other seed treatments were used to control rice seedling blight. In February 1970 the U.S. Department of Agriculture suspended certain mercury-based seed treatments. Ceresan L, a mercurial fungicide, at about 0.75 g/kg (1.2 oz/100 lb) of seed was used in addition to aldrin until supplies were exhausted in 1972. Terra-Coat L-205, a nonmercurial fungicide applied at the rate of 1.38 g/kg (2.2 oz/100 lb) eplaced Ceresan L from 1973-75. Vitavax-R (another nonmercurial fungicide) at 2.19 g/kg (3.5 oz/100 lb) of seed 94 J. Wildl. Manage. 43(1):1979 This content downloaded from 207.46.13.148 on Sun, 11 Sep 2016 04:33:56 UTC All use subject to http://about.jstor.org/terms EFFECTS OF ALDRIN ON SNOW GEESE& Flickinger 95 replaced Terra-Coat L-205 in 1976 because it was less expensive. Seed treatment and rainfall differed each year. In 1972 aldrin-Ceresan L treated seed was planted in all rice fields (treated fields) on the west side while seed treated only with Ceresan L was planted in several large fields (untreated fields) on the east side of the study area. A heavy rain on 21 March flooded all rice fields sufficiently for seed germination. Planting was delayed in 1973 by frequent rains in early March and planting of aldrin-treated seed did not begin until 3 April, after nearly all geese had migrated northward. In 1974, rain on 25 March flooded all fields planted with aldrintreated rice seed. No aldrin-treated rice seed was planted in 1975 and 1976. Geese were exposed to aldrin-treated rice seed only in 1972 and 1974. Snow geese and some white-fronted (Anser albifrons) and Canada geese (Branta canadensis) spent winters on the study area concentrated near the reservoirs. Most arrived in late October and left for nesting grounds in mid-March. They spent most of the fall and early winter gleaning rice stubble fields. In late winter they rested on the reservoirs during midday and fed in pastures and rice stubble fields in the morning and afternoon. Some geese preferred pastures for feeding. Few visited dry planted rice fields; most were attracted to newly planted rice fields only after flooding (in late March) which occurred from 3 to 24 days after they were planted. After rains on 21 March 1972 and 25 March 1974, and until the remaining geese left for nesting grounds, most geese fed in flooded, treated fields.