Geology topics

William M. Iko

Publications and source records attributed to William M. Iko.

3 recordsLinked to original sources

USGS2011

Severe bill deformity of an American Kestrel wintering in California

During a recent survey for West Nile virus in wild birds around the Sonny Bono Salton Sea National Wildlife Refuge, Imperial County, California (Dusek et al. 2010), we captured a female American Kestrel ( Falco sparverius ) with a severe bill deformity (Figure 1). The kestrel was captured on 9 March 2006, at 08:45, approximately 0.25 km south of the intersection of Wiest and Lindsey roads (33° 08' 42' N, 115° 26' 59' W) and 6 km east-northeast of Calipatria. It was caught on a bal-chatri trap baited with a domestic mouse (Berger and Mueller 1959), as were all the 208 kestrels captured during this study. The bird was initially perched on a high transmission line running along Wiest Road and was caught within 10 minutes of our setting the trap. In examining the bird, we observed that the maxilla beyond the cere was missing. The upper bill structure from the palatine process, which included part of the maxilla, the entire premaxilla, and the external rhamphotheca (the hardened keratin layer cover ing the premaxilla) was missing rostral to the bird's cere and nares (Threlfall 1968, Lucas and Stettenheim 1972, Proctor and Lynch 1993). The epidermal layer of the cere appeared to have fused over the remaining area between the nares where the upper bill normally would have been. The deformation did not appear to be recent or related to our trapping, as there were no obvious abrasions or open wounds in the region surrounding the nares and oropharynx or signs of recent trauma surrounding the oropharynx area. Both nares were clearly defined, and the tongue protruded from the open oropharynx area. After completing the physical examination, measurements, and obtaining a blood sample for testing for West Nile virus, we released the kestrel at the location of capture. After its release, we monitored the kestrel's behavior for approximately 30 minutes but did not observe any additional hunting.

California↗

USGS1992

Non-random pairing in American kestrels: mate choice versus intra-sexual competition

Natural selection may influence the arrangement of individuals into mated pairs through either inter-sexual (mate choice) or intra-sexual selection (competition). A study of the American kestrel, Falco sparverius , in northern Saskatchewan distinguished between these two processes using size as a measure of the bird's competitive ability, and condition (mass scaled to body size) as an index of quality. Both sexes arrive on the study area after spring migration in equal numbers and males establish territories. Males and females that moved among territories at the time of pair formation were not different in size or condition from those that did not move, suggesting that birds were not being displaced by superior competitors, and that females moved to encounter potential mates. Within mated pairs, there was no relationship between a bird's size and the condition of its mate for either sex as would be predicted if intra-sexual competitition explained mating patterns. Instead, there was positive assortative mating by condition, suggesting that both sexes used quality as the criterion in choosing mates. There was no correlation between the sizes of males and females in mated paird. Because there were no differences in size or condition of breeding and non-breeding males, factors other than physical attributes, such as prior experience with the area, may determine a male's success in obtaining a territory. Because females that did not obtain mates were in poorer condition than those that did, males may have rejected poor quality females. The results suggest that intra-sexual competition was not important for pair formation, and that kestrels chose mates on the basis of quality.

Animal Behaviour↗

USGS1991

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.

Canadian Journal of Zoology↗