Long-billed Curlew (Numenius americanus): a technical Conservation Assessment Prepared for the usda forest Service, Rocky Mountain Region, Species Conservation Project December 12, 2006 James A. Sedgwick
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20 21 habitat. Returning breeders establish a territory with less agonistic interaction than first-time breeders, and some reports suggest that some males and females may arrive already paired (Wolfe 1931, Forsythe 1970). If unpaired, pair formation occurs shortly after arrival on breeding areas as males establish territories and begin aerial displays to advertise their unpaired status (Allen 1980, Jenni et al. 1981, Pampush 1981). Unpaired females arrive later than males and previously paired females (Allen 1980, Jenni et al. 1981). Pair formation on the breeding grounds is highlighted by a conspicuous aerial display. Courtship includes several distinct behaviors: v During the Bounding-SKK flight (following Allen 1980) or the Undulating Flight Display (following Jenni et al. 1981), the male climbs silently and steeply (over 45°) into the air with rapid, fluttering wing-beats to a height of 10 to 15 m. He then slowly glides downward in this position, often coming to within 0.3 m of the ground before ascending again. Soft “kerr-kerr” or “hee-who” calls are given during flight (Allen 1980). Unpaired males perform this display much more frequently than paired birds. v Ground-Calling, during which high-pitched and melodious calls are given, is performed primarily by unpaired males to attract females. v Ritualized Scraping, during which numerous nest bowls scattered around the territory are produced, is performed by both sexes during courtship (King 1978); however, Jenni et al. (1981) noted only males making scrapes. v During Tossing, a nest-building movement that is performed by both sexes, bits of vegetation, sticks, rocks, or other nesting materials are tossed into the nest scrape. v The Courtship Run is a precopulatory behavior performed by males, where the male runs at the female with neck retracted, head upright, bill parallel to ground, and wings sometimes slightly raised with primaries fanned. v
precopulatory display performed by males. The male stands behind the female, with tail cocked upward, neck outstretched, and angle of back horizontal. The male then begins paddling his feet rapidly, moving side to side behind the female. Simultaneously, the male shakes his head and bill, ruffling the female’s shoulder-feathers. Bill-shaking is so vigorous that the male’s bill appears to vibrate (King 1978). The male strokes both sides of the female and sometimes her undertail coverts. Movements of the male become more frenzied as the display progresses. Bill- stroking can last more than a minute (King 1978). If the female does not walk away during the Shaking Display, she may assume a more horizontal body position, and the male will then mount the female for copulation. The proportion of displaying males that fail to acquire mates varies among breeding areas. Unpaired males constituted up to 20 percent of the total population in Oregon (Pampush 1980). In southeastern Washington (Allen 1980) and Colorado (King 1978), all males were paired in one year, but in another year, unpaired males held territories as commonly as pairs. More males than females were always observed during spring surveys in Idaho, suggesting that only 79 to 85 percent of the males paired each year (Jenni et al. 1981). During spring surveys in two locations in western Wyoming, males outnumbered females 1.7:1 and 3.0:1, but the high male:female ratios observed during surveys may have been due to differences in visibility of the sexes during spring when females are laying and incubating eggs (Jenni et al. 1981). The female curlew selects the nest site from several scrapes available within the territory. The nest bowl is a shallow depression in the ground. Males appear to initiate most nest-building with scraping behavior related to courtship (Jenni et al. 1981), but females will participate once the scrape has been initiated. To construct the nest scrape, the individual drops down onto its breast with its wings held slightly away from the body. With the bill directed forward and diagonally downward, the feet are rapidly kicked backward alternately, forming a shallow depression. Often multiple scrapes in various stages of development occur within a territory. After the scrape is complete, the nest is lined, primarily by the female; construction of the lining usually continues through egg-laying, well into incubation (King 1978, Jenni et al. 1981). Nest-lining material is variable and includes small pebbles, bark, livestock droppings, grass, rabbit and Canada goose (Branta canadensis) droppings,
20 21 small stems, twigs, seeds, and cheatgrass leaves (Wolfe 1931, Allen 1980, Jenni et al. 1981, Campbell et al. 1990). Some nests are quite substantial while others are only sparsely lined, depending on the availability of nesting material (Allen 1980). Of 59 nest scrapes in southeastern Washington, the average depth was 4.6 cm ± 1.1 SE (range = 2.3–6.6), and the average diameter was 20.1 mm ± 3.7 SE (Allen 1980). In southeastern Colorado, the average scrape diameter of seven nests was 18.6 cm ± 5.2 SD (range = 8–23) and the average depth was 7.1 cm ± 1.1 SD (range = 6–9) (King 1978). Nests were placed on west-by-southwest-facing slopes more often than expected in western Idaho (mean aspect = 229° from true north, n = 123; Jenni et al. 1981). Long-billed curlew eggs are oval to pyriform, generally smooth, non-glossy to glossy, and have a light beige to greenish to olive background color. They are heavily speckled, spotted, or scrawled with dark olive-brown or pale purple-gray, with a tendency for the markings to be heavier and more numerous at the large end of the egg (Dugger and Dugger 2002). In Utah, length and breadth of eggs (n = 50) was 66.0 mm (range = 59.6–74.1) x 47.4 mm (range 42.2–50.2; Sugden 1933). In Idaho (n = 271), mean length was 65.3 ± 0.17 SE, breadth was 46.1 ± 0.08 SE, and volume was 66.2 cm 3
greater among females than within clutches (Redmond 1986). Pre-DDT (1888–1944) eggshell thickness (0.300 mm ± 0.005 SE, n = 28 eggs) in California and Oregon was greater than post-DDT thickness (0.281 mm ± 0.003 SE, n = 17, 1951–1952; and 0.298 ± 0.007, n = 7, 1978–1979), but eggshell thinning was below the level associated with population declines in other species (Blus et al. 1985). In Utah, thickness was not different pre-DDT (shell thickness index = 1.45 ± 0.011 SE; n = 77 eggs from 21 clutches) versus post-DDT (index = 1.43 ± 0.014 SE; n = 50 eggs from 13 clutches) (Morrison and Kiff 1979). In Idaho, egg laying occurs in the middle of the day (1100–1500) and not at daily intervals (4-egg clutches are laid in 5 to 7 days; Jenni et al. 1981). In Washington, laying is within 2 hours of dawn on alternate days (Allen 1980). Females spend little time on nests until clutches are complete. Males often sit on incomplete clutches during egg laying, but it is unclear if they are incubating. Courtship continues through laying. Curlews will continue laying in another nest if the first nest is destroyed during laying. Incubation begins in earnest when the clutch is complete (Allen 1980, Jenni et al. 1981), but it may be intermittent during egg laying (Graul 1971). Both the male and female incubate (Graul 1971, Allen 1980, Jenni et al. 1981). In southeastern Washington and Idaho, females generally incubated during the day, and males incubated at night (Allen 1980, Jenni et al. 1981). Nest relief occurs about the same time each day unless the pair is disturbed. In Washington, morning exchange periods were either between 0500 and 620 or between 0900 and 1015; the evening exchange period was between 1700 and 1930 (Allen 1980). Adults may sit continuously during their incubation shift, exposing the eggs only during changeover periods. On hot days, the attending adult shades the eggs rather than incubating
develop incubation patches. The incubation period has been reported as 29 days (range = 28–31, n = 10, southeastern Oregon; Pampush and Anthony 1993) and 27 days (n = 4, Utah; Forsythe 1972). Hatching is highly synchronous, and occurs during a 4 to 6 hour period (Allen 1980, Jenni et al. 1981). The adult removes eggshells soon after hatching by grasping them with its bill and flying several meters before alighting to drop them. Each shell is dropped in a different spot, not always in the same direction from the nest (Graul 1973, Allen 1980). The newly hatched young are precocial, covered in down, and their eyes are open; they are able to walk 5 hours after hatch and able to feed at 10 hours. The iris is chocolate-brown, and the tarsi and feet are light gray tinged with pink. The upper mandible is black from tip to nares, and grayish pink from nares to base; the distal half of the lower mandible is gray, and the proximal half is reddish pink (Forsythe 1973). Newly hatched young generally dry within 3 hours and leave the nest within a few hours of hatching (Allen 1980, Jenni et al. 1981). Young, just-hatched birds may leave the nest, rest in grass, and then return to be brooded for short periods. During nest departure, the male stands some distance away in the direction the young will move, as the female calls to the chicks while standing near the nest (Allen 1980). Mean mass at hatching in southeastern Washington (Numenius americanus parvus) was 49.7 g ± 0.69 SE (range = 44–56; Allen 1980). In Colorado (N. a. americanus), mean mass was 63.3 g (n = 3 chicks from one nest; Graul 1971), and in Utah it was 56.5 g (n = 3 chicks from one nest; Forsythe 1973). Limited data (n = 3) suggest that the tarsus grows faster than the culmen, possibly because of the need for well- coordinated movement for feeding and predator avoidance. Feathers appear in the alar tract at 11 days and the caudal tract at 14 days (Forsythe 1973). Chicks
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