| Description |
The ecology study pertained to the breeding biology and behavior of the Green-tailed Towhee (Chlorura chlorura). The species is a summer resident of the mountain shrub belt of the foothills and mountains of the western states. It winters in southern portions of California, Arizona, Texas, as well as central Mexico The area studied is located 15 miles east of Salt Lake City, Utah in the Wasatch Mountain range, at an elevation of 6,000 feet. This area was "good" towhee habitat, with low shrubs :growing among the many wild flowers and grasses. In this habitat male Green-tailed Towhees established their territories which were maintained by territorial song. The average size of a ,territory was 9,700 square feet, thus ,approximately 147 yards by 215 yards. Males, while migrating to their nesting grounds estalish, toward the latter part of ' the migration, pre-territores. These are loosely formed areas chosen at resting spots. This behavior seemingly leads to rapi4 territorial establishment when they finally arrive on their permanent nesting grounds. A I though the sexes are indistinguishable to the eye, measurable differences were found in study skins. The wing of males averaged 77.4 mm, while females averaged 74.5 mm. Tail lengths were 83.2 and 80.2 mm respectively. Pair bonds are formed shortly after the female arrives at the nesting grounds, approximately 2 to 3 days after the male. The bond is for one "season. After mating, the female performs all the x nest duties, entailing selection of nest site, construction of nest and incubation of eggs. The male merely patrols his territory. Normally, only one clutch of eggs is laid and one brood of young raised. If some disturbance leads to abandonment of a nest or if young are destroyed in early developmental stages or are taken by predators, renesting occurs. Ten nests were located during a two year period. All were placed in sagebrush (Artemisia tridentata Nutt.). The average height of the nest above the ground was 46 cm from rim of cup to the ground The eggs were laid on constitute days with an average clutch size of 3.3. Incubation period was 12 days. The young are trial when hatched and are covered with a dark, sparse down:; The activity of the male in proclaiming his territoriality marked ... lye decreases as construction of nest, egg laying and incubation are consummated. However, in contrast to the early indifference toward the nest and eggs during the nestling period, the male takes an active part in feeding the young and in cleaning the nest. Both parents are coprophagic of the feces of the young, in other Words, disposing of the fecal sacs by ingesting them. Nestlings fledged after 10 days in the nest. Fledglings are ca red for by both pa rents for an undetermined length of ti me. They were fed insects. On a year-round basis, the diet of adults is mixed, 57% animal material and 47% plant. Reproductive success is influenced largely by predation on the young while in the nest. The predation in the study area was high. Only three of the ten nests observed produced young that fledged. Five were lost to predators. The principal predator seemed to be the magpie (Pi ca pica (Linnaeus). Other mortality pertained to one being abandoned because of inclement Weather and one: was abandoned seemingly because of the observer's presence. There are certain lines of evidence that support the placing of the Green-tailed Towhee in the genus Pipilo, namely coprophagy, the juvenal plumage, flight patterns, type of habitat chosen, .and feeding patterns which are all very similar ,to the Rufous-sided, Towhee. |
