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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
Shaking (King 1978, Allen 1980) is also a
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,
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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
± 0.32 SE; variation in egg size was significantly
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
per se (Jenni et al. 1981). Presumably, both sexes
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