This study was designed to determine if, by providing artificial nest sites, a raptorial predator could be attracted into an area where suitable sites are limited. The American Kestrel (Falco sparverius) was a common species in the area and nest boxes designed for their use were placed in three vegetational types in western Utah and eastern Nevada. Seventy boxes were available in 1975 and 110 in 1976. Kestrels nested both years in the salt-desert shrub community but were absent from the pinyon-juniper and riparian areas. Four other bird species nested in the latter two areas, however. In 1975 the nesting success was affected by severe weather including unseasonable cold and snow. In 1976 interaction with and predation by rodents affected utilization and success. Other factors such as existing hole-nesting populations, size, construction, and placement of the box also affect the rate of occupancy and number of boxes used.

In order to test the hypotheses: (1) that the digestive absorption of fluoride (F) is affected by the presence of aluminum (Al), and (2) that the distribution of F absorbed among organs/tissues is affected by Al, 36 American kestrels (Falco sparverius) were randomly divided into 6 groups of 6, and given oral doses daily for 30 days according to the following scheme: (1) deionized water only, (2) 30 mg/kg F$ sp-$, (3) 24 mg/kg F$ sp-$, (4) 24 mg/kg Al$ sp{3+}$, (5) 30 mg/kg F$ sp-$ + 24 mg/kg Al$ sp{3+},$ (6) 24 mg/kg F$ sp-$ + 24 mg/kg Al$ sp{3+}$. Excreta was collected every 24 hours between dosing. Femurae, kidneys, hearts, alimentary canals, skeletal muscle, and livers were obtained from all birds at the end of experiment. All samples were analyzed for F, Al, total phosphate (P) and calcium (Ca). F excretion was significantly higher in birds given 30 mg/kg F$ sp-$ + 24 mg/kg Al$ sp{3+}$ than in their counterparts which received the same amount of either F or Al alone (p $<$ 0.05). Excretion of Al was also elevated in all groups (except those only given water) from the level of excretion before the experiment commenced (p $<$ 0.05), despite the fact that 2 groups out of those 5 received F only. P and Ca contents of excreta were not affected by the oral dose. F contents in femurae from groups receiving both F and Al were significantly lower compared to those levels in those birds which were given F only (p $<$ 0.05). Significantly more Al was found in kidneys from the group receiving 30 mg/kg F$ sp-$ + 24 mg/kg Al$ sp{3+}$ than in those groups given only 1 of the 2 ions (p $<$ 0.05).

The ability to accurately identify individuals is required for the detailed study of animals. Numerous artificial markers have been developed for this purpose. Negative effects on survival, reproductive success and behavior have been reported for most marking methods, significantly affecting the very parameters being studied. / Birds of prey have suffered the shortcomings of artificial marking methods. In light of the known and potential deleterious effects of marking, attention has been focused on developing new techniques to identify individual raptors without attaching artificial markers. / This study investigated the use of tarsal scale patterns as unique individual identifiers in birds of prey. The American kestrel (Falco sparverius) was chosen as a model. Both legs of seventy-five kestrels were photographed over a two-year period. / Photographic comparisons of 150 scale patterns demonstrated the uniqueness of each and therefore its ability to be used as an individual's natural identifier. Furthermore, patterns were found to remain unchanged from one year to the next. These findings support the hypotheses that tarsal scale patterns are unique to each bird and do not change over time. / A method of coding the tarsal scale patterns was developed. These codes can be used in a computerized data base to significantly enhance the speed of pattern searches.

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This project investigated postnatal development of the adrenocortical function in captive American kestrels (Falco sparverius) employing measurements of basal and stress-induced levels of corticosterone at specific developmental stages. Chicks aged 10-days exhibited partially functioning adrenocortical systems with baseline levels comparable to adults. The ability to respond to external stressors increased through postnatal development and by the age of 22 days, stress-induced maximal levels of corticosterone were indistinguishable from those of one-year old adults, and levels of 28-day old birds were significantly higher than these adults. In addition, baseline and maximum stress-induced levels of corticosterone at all ages were significantly higher in first-hatched chicks than all other siblings and these effects grew stronger through development. These results suggest that the brain-pituitary-adrenal axis in this semi-altricial species is (1) already partially developed in young chicks and (2) only becomes fully functional when behavioral and neuromuscular development is nearly complete. Furthermore, results from this study suggest that hatching asynchrony has an effect on this variation in stress-induced maximal levels of corticosterone during the latter half of postnatal development, with a higher degree of hatching asynchrony leading to larger disparity in adrenocortical function between first- and fourth-hatched chicks. This adrenocortical disparity resulting from female-mediated hatching asynchrony may potentially lead to both brood-reduction and brood survival under diametric food conditions, ensuring that the female's reproductive fitness is maximized in varying habitats. Variation of adrenocortical function among siblings may increase female efficiency in raising a brood of fit chicks, maximizing her reproductive success.

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