The breeding range of the Black Skimmer in the United States stretches from Massachusetts
to Florida on the Atlantic Coast, Florida to Texas on the Gulf Coast, and locally in
southern California on the Pacific Coast (Field Guide to Birds of North America 1987). Skimmers are locally common to uncommon on
beaches, estuaries, bays, and lagoons; they occasionally appear inland in Texas on fresh
water lakes and streams, mostly following tropical storms (Texas Ornithological Society
1995). Black Skimmers in Texas nest
colonially with terns and gulls and are gregarious during all seasons, especially in fall
and winter (Oberholser 1974, White et al. 1984). Skimmers
winter along the coast from North Carolina to Texas, but in fewer numbers; most migrate
south to Latin America along the Gulf and Pacific Coasts.
Skimmers apparently cross large land masses during fall migration because
some birds banded as juveniles in Texas were recovered on the Pacific Coast of Mexico and
Guatemala (D. H. White, pers. obs.).
DISTRIBUTION: In Texas, the breeding range of the Black Skimmer
extends for over 800 km (500 mi) along the Gulf Coast.
The TBBAP has confirmed breeding (89% of total nest records) in all of
Texas's coastal counties (latilongs 29093, 29094, 29095, 28095, 28096, 28097, 27097,
26097) and at several inland sites (latilong 26099, quads E-2 and F-2; and latilong 26097,
quads E-7 and E-8). Despite considerable
heterogeneity among years, census summaries indicate that about 35% of the breeding
population occurs on the upper coast, 16% on the central coast, and 49% on the lower coast
(Texas Colonial Waterbird Society 1982, Texas Parks and Wildlife Dept. 1992). Estimates of individual colony size also vary
widely, depending upon the locality. Nest
count totals during four seasons in the vicinities of Corpus Christi, Port Mansfield, and
Laguna Vista ranged from 31 to 122, 36 to 84, and 28 to 30, respectively (White et al.
1984).
SEASONAL
OCCURRENCE: Black Skimmers have a long
breeding season in Texas, spanning seven months for some pairs. Birds begin congregating in mid-March and egg
laying commences between mid-April and mid-May; there is a high degree of consistency in
the initiation of egg laying among Texas
colonies, but much variation among years (White et al. 1984). The incubation period averages 21 days, with a
range of 20-23 days (DePue 1974, White et al. 1984).
The TBBAP dates for nests with eggs are 5 May-6 June, with young in nests
until 5 July. Most skimmer chicks fledge by
the end of August or early September at 4-5 weeks of age; they leave the nesting areas
within a week. Searches to locate fledged
young in Texas were unsuccessful (White et al. 1984).
Shortly after the fledglings left, so did adults, unlike skimmers in New
York, which formed mixed-aged flocks that remained on nesting islands for up to several
months (Gochfeld 1978).
BREEDING
HABITAT: Black Skimmers in Texas nest
primarily on sandy or shell covered beaches of natural and man-made islands (Oberholser
1974, White et al. 1984). On the upper coast,
they occasionally nest on pebble
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or
shell covered roof tops and parking lots (D. H. White, pers. obs.). Nests are slight depressions in the sand or shell
about 15-25 cm (6-10 in) wide and are devoid of nest material. Skimmers usually nest near the high tide mark,
often resulting in inundation of nests by storm tides, excessive rain, or wave action
(White et al. 1984). Nest site tenacity is
strong; up to three attempts to renest may occur at the same locale. Invariably, nests are moved further up the beach
with each attempt. After a washout, renesting
occurs within a week and the number of new nests with eggs is similar to the number that
was destroyed; however, renest attempts have less success and smaller clutch sizes than
successful first attempts. Nest initiation
ceases after early August and skimmers raise only one brood. Nesting associates in Texas colonies include gulls
and terns, but depredation is low. Egg loss
in only 3 of 510 nests was attributed to avian predators (White et al. 1984), and there
was no evidence of mammalian or reptilian predators on the islands.
STATUS:
The Breeding Bird Survey (BBS) data (Sauer et al. 1997, accessed 7/21/98) indicate a
survey-wide increase of 33% in skimmer numbers during 1966-1996, but a 1.5% yearly
decrease in numbers during this period on the central and lower Texas coasts. Data from the Texas Colonial Waterbird Society
(1982) also suggest that the breeding population of Black Skimmers in Texas is slowly
declining. Between 1974 and 1980, numbers of
breeding pairs for the Texas coast declined 24%, from 11,540 to 8760. More recent census estimates indicate a further
decline (Texas Parks and Wildlife Dept. 1992). The
1992 census tallied only 7145 breeding pairs for the entire Texas coast, a decline of 18%
from the 1980 figure and an overall decline of 38% since 1974. The reasons for the presumed declines in
Texas are unknown. White et al. (1984)
suspected pesticides in Texas birds because 36% of females on the central and lower coasts
laid eggs with ?10 ppm DDE. However, there
was no significant (P < 0.05) relationship between residues in eggs and fledging
success, and eggshell thinning in skimmers was negligible.
Also, successful nest attempts in Texas resulted in 1.3 fledglings per nest,
higher than those reported for skimmers elsewhere (Erwin 1977, Blus and Stafford 1980,
Burger 1982). Flooding appeared to be the
major limiting factor governing nest success in Texas, as reported elsewhere, but this is
a recurring natural phenomenon. There must be
other reasons for the gradual population decline in Texas.
It is likely that the effects of human encroachment are responsible. Although Black Skimmers still are fairly common in
Texas, their status should be monitored closely in the future.
Text by Donald H. White (ca. 1998) |
