Nestling American Kestrels Research Articles

Developmental toxicity of diphenyl ether herbicides in nestling American kestrels

Beginning the day after hatching, American kestrel (Falco sparverius) nestlings were orally dosed for 10 consecutive days with 5 microliters/g of corn oil (controls) or one of the diphenyl ether herbicides (nitrofen, bifenox, or oxyfluorfen) at concentrations of 10, 50, 250, or 500 mg/kg in corn oil. At 500 mg/kg, nitrofen resulted in complete nestling mortality, bifenox in high (66%) mortality, and oxyfluorfen in no mortality. Nitrofen at 250 mg/kg reduced nestling growth as reflected by decreased body weight, crown-rump length, and bone lengths including humerus, radius-ulna, femur, and tibiotarsus. Bifenox at 250 mg/kg had less effect on growth than nitrofen, but crown-rump, humerus, radius-ulna, and femur were significantly shorter than controls. Liver weight as a percent of body weight increased with 50 and 250 mg/kg nitrofen. Other manifestations of impending hepatotoxicity following nitrofen ingestion included increased hepatic GSH peroxidase activity in all nitrofen-treated groups, and increased plasma enzyme activities for ALT, AST, and LDH-L in the 250-mg/kg group. Bifenox ingestion resulted in increased hepatic GSH peroxidase activity in the 50- and 250-mg/kg groups. Nitrofen exposure also resulted in an increase in total plasma thyroxine (T4) concentration. These findings suggest that altricial nestlings are more sensitive to diphenyl ether herbicides than young or adult birds of precocial species.

Cannibalism of nestling American kestrels by their parents and siblings

We examined the frequency of cannibalism of nestling American kestrels (Falco sparverius) in north-central Saskatchewan. We investigated human disturbance and food shortages as possible causes of it. Cannibalism of nestlings by their parents and siblings was confirmed by observation and by the presence of partially eaten carcasses, or inferred from the sudden disappearance of a nestling between frequent nest checks. Cannibalism occurred at 8% of 48 nests in 1988, and 18% of 92 nests in 1989. Not all nestlings that died were cannibalized. Where nestling mortality occurred, carcasses were eaten in at least 20% of nests in 1988, and 63% of nests in 1989. The chicks that were cannibalized died at a significantly younger age than those that died but were not cannibalized. The mass and age of the parent and the laying date were not associated with the occurrence of cannibalism. We found no strong evidence of a causal link between human disturbance and nestling mortality or cannibalism; however, the abundance of small mammal prey was inversely related to the frequency of cannibalism between years, and there were fewer prey and lower prey delivery rates in territories where cannibalism occurred than in territories where nestling mortality did not occur. The fact that some nestlings died but were not eaten suggests that such mortality was unrelated to food shortages. The food advantage of cannibalism may not outweigh potential disadvantages such as disease transmission.

Biochemical and hematological effects of lead ingestion in nestling American kestrels (Falco sparverius).

One-day old American kestrel (Falco sparverius) nestlings were orally dosed daily with 5 microliters/g of corn oil (controls), 25, 125 or 625 mg/kg of metallic lead in corn oil for 10 days. Forty per cent of the nestlings receiving 625 mg/kg of lead died after 6 days and growth rates were significantly depressed in the two highest lead dosed groups. At 10 days hematocrit values were significantly lower in the two highest lead treated groups, and hemoglobin content and red blood cell delta-aminolevulinic acid dehydratase (ALAD) activity was depressed in all lead treated groups. Plasma creatine phosphokinase decreased in the two highest treatment groups. Brain, liver and kidney ALAD activities, brain RNA to protein ratio and liver protein concentration decreased after lead exposure whereas liver DNA, DNA to RNA ratio and DNA to protein ratio increased. Brain monoamine oxidase and ATPase were not significantly altered. Measurements of the ontogeny of hematological variants and enzymes in normal development, using additional untreated nestlings, revealed decreases in red blood cell ALAD, plasma aspartate amino transferase, lactate dehydrogenase, brain DNA and RNA and liver DNA, whereas hematocrit, hemoglobin, plasma alkaline phosphatase, brain monoamine oxidase, brain ALAD and liver ALAD increased during the first 10 days of posthatching development. Biochemical and hematological alterations were more severe than those reported in adult kestrels or precocial young birds exposed to lead. Alterations may be due in part to delayed development.

Survival, growth, and accumulation of ingested lead in nestling American Kestrels (Falco sparverius)

One-day old American Kestrel (Falco sparverius) nestlings were dosed orally daily with 5 μl/g of corn oil (controls), 25 mg/kg, 125 mg/kg, or 625 mg/kg of metallic lead in corn oil through day 10. Forty percent of the nestlings given 625 mg/kg died after six days. Growth rates became significantly different from controls in the 625 mg/kg group by day 3 and in the 125 mg/kg group by day 4. Crown-rump lengths and brain weights were significantly lower in both treatment groups. Liver and kidney weights were lower in the 625 mg/kg groups. Skeletal examination and measurement of alizarin red-S stained nestlings revealed reduced growth for the humerus, radius-ulna, femur, and tibiotarsus in the 125 mg/kg and 625 mg/kg groups. Skeletons were otherwise normal in appearance. Greater than 2 ppm (wet weight) lead in the liver or 6 ppm in the kidney was associated with suppressed growth, while more than 5 ppm in the liver and 15 ppm in the kidney occurred in survivors in the 625 mg/kg group. The order of accumulation of lead in tissues at the end of 10 days was kidney > liver > brain. These findings suggest that altricial nestlings may be considerably more sensitive to lead exposure than adults and also more sensitive than hatchlings of many precocial species.