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Thomas W. Aldrich

Publications and source records attributed to Thomas W. Aldrich.

7 recordsLinked to original sources
USGS1992

Survival of cackling Canada geese, 1982-1988

We estimated seasonal and annual survival rates of cackling Canada geese ( Branta canadensis minima ) for the period 1982-1989 to identify periods of high mortality and assess effects of harvest management decisions. We tested hypotheses about age- and sex specific variation in survival, seasonal variation in survival rates, and variation in survival between years in which hunting seasons were open and closed. Geese were marked with individually identifiable neckbands and observed from autumn through spring. We used these data to estimate survival rates for 3-month periods in early (EW) and late (LW) winter and a 6-month period in summer (SU). Mean annual survival rates of immature females were lower than those of adults over the entire study. Survival rates of immature males were lower than those of adults during the 2 years with sport hunting seasons. We found no evidence of sex-specific differences in seasonal or annual survival rates of immature geese. Mean survival rates of adult males and females were similar during EW and LW, but there was evidence of higher survival of females during SU. Annual survival rates of adult females were higher than those of adult males. Mean annual survival rates of adult females and immatures of both sexes were lower in the years during which sport hunting was permitted. Tests for different survival rates in years before and after an agreement with the Eskimos to cease summer hunting yielded equivocal results.

Alaska, California↗
USGS1988

Selenium teratogenesis in natural populations of aquatic birds in central California

The frequency and types of malformations are described that were encountered during the spring of 1983 in a natural population of aquatic birds exposed to agricultural drainwater ponds and food items containing high concentrations of selenium in central California. A total of 347 nests of aquatic birds containing 1,681 eggs was selected for study at Kesterson Reservoir located in the Kesterson National Wildlife Refuge (NWR), Merced County, California. Embryos collected during incubation or from eggs that failed to hatch were examined to determine the age at death and presence of malformations. Embryonic death was generally high; approximately 17–60% of the nests of different species contained at least one dead embryo. The incidence of malformed embryos was also high; approximately 22–65% of the nests where at least two embryos were examined contained abnormal embryos. American coots ( Fulica americana ) and black-necked stilts ( Himantopus mexicanus ) experienced the highest incidence of malformed embryos. For all species, the average percentage of eggs containing dead or live abnormal embryos was 16.1 whereas the average percentage containing live abnormal embryos was 10.7. Multiple gross malformations of the eyes, brain, and feet were often present. Brain defects included hydrocephaly and exencephaly. Eye defects included both unilateral and bilateral anophthalmia and microphthalmia. Eye and foot defects with ectrodactyly and swollen joints were the most common in coots. Beak defects also occurred frequently and most often included incomplete development of the lower beak of ducks ( Anas spp.) and stilts. Wing and leg defects were most prevalent in stilts and ducks, with ectromelia and amelia most prevalent in stilts. Other malformations occurring at lower frequencies included enlarged hearts with thin ventricular walls, liver hypopiasia, and gastroschisis. Based upon simultaneous examination of a control population of aquatic birds of the same species and published studies, the incidences of embryonic mortality and deformities were 9–30 times greater than expected. The role of the form of selenium responsible for teratogenesis in laboratory studies is discussed.

California↗
USGS1988

Bioaccumulation of selenium by snakes and frogs in the San Joaquin Valley, California

Livers of gopher snakes (Pituophis melanoleucus) from Kesterson Reservoir (Merced County, California) contained significantly higher mean selenium concentrations (11.1 .mu.g/g, dry weight) than those from two nearby reference sites (2.05 and 2.14 .mu.g/g). Livers of bullfrogs (Rana catesbeiana) collected from the San Luis Drain at Kersterson Reservoir also contained significantly higher mean selenium concentrations (45.0 .mu.g/g) than those from nearby reference sites (6.22 .mu.g/g). The high levels of selenium bioaccumulation in these snakes and frogs at Kersterson Reservoir reflected the elevated levels found in their food organisms. We did not examine that snakes or frogs from Kesterson for signs of ill health, but the concentrations we found were sufficiently high to warrant concern about potential adverse effects in these animals and their predators.

Copeia↗
USGS1987

Selenium contamination of the Grasslands, a major California waterfowl area

In a recent study at Kesterson Reservoir in California, selenium was shown to cause mortality and deformities in embryos of aquatic birds. The present study was conducted to determine if selenium or other contaminants in agricultural drainwater used for marsh management were likely to cause similar adverse effects in the nearby Grasslands area. Selenium concentrations were elevated (greater than 15 ppm, dry-weight) in livers of some birds of all species collected from the Grasslands. Mean selenium concentrations in all species sampled in the South Grasslands were significantly higher (P less than 0.05) than those from the 'control site', the Volta Wildlife Area. Mean selenium levels in black-necked stilts (Himantopus mexicanus) from the South Grasslands (35.6 ppm) were similar (P greater than 0.05) to levels in stilts from Kesterson (46.4 ppm), but means for American avocets (Recurvirostra americana) from the South Grasslands (67.3 ppm) were higher (P less than 0.05) than those from Kesterson (28.4 ppm). Bird eggs and fish from the Grasslands also contained elevated levels of selenium. Concentrations of eight heavy metals in fish generally reflected those patterns previously found in water entering the study areas. Of the organochlorines detected in fish, only DDE occurred at concentrations potentially harmful to birds (6.1 and 3.0 ppm, wet weight, at two South Grassland sites). The effect on avian health or reproduction of the other contaminants, singly or in combination, could not be determined. However, selenium levels were apparently sufficiently elevated in 1984 to have caused adverse effects on avian reproduction in the South Grasslands.

California↗
USGS1986

Embryonic mortality and abnormalities of aquatic birds: Apparent impacts of selenium from irrigation drainwater

Severe reproductive impacts were found in aquatic birds nesting on irrigation drainwater ponds in the San Joaquin Valley of California. Of 347 nests studied to late incubation or to hatching, 40.6% had at least one dead embryo and 19.6% had at least one embryo or chick with an obvious external anomaly. The deformities were often multiple and included missing or abnormal eyes, beaks, wings, legs and feet. Brain, heart, liver and skeletal anomalies were also present. Mean selenium concentrations in plants, invertebrates, and fish from the ponds were 22–175 ppm (dry weight), about 12 to 130 times those found at a nearby control area. Bird eggs (2.2–110 ppm) and livers (19–130 ppm) also contained elevated levels of selenium. Aquatic birds may experience similar problems in other areas where selenium occurs at elevated levels.

California↗