Nature Of Migration In The Species
Short- to intermediate-distance migrant between breeding sites in coastal west Alaska and wintering range along Pacific Coast from Alaska to Mexico. Northward migration coastal beginning late March-early April. Large portion of population stages in Prince William Sound, Alaska, last week of April and first week of May before continuing to breeding grounds. Failed breeders leave breeding grounds beginning late June followed by successful breeders; juveniles last to leave in August-September. Movement south fairly rapid. Most individuals return to same wintering site each year.
Timing And Routes Of Migration
Coastal between mid-March and mid-May. Isolated interior records from Oregon and Salton Sea region, California; latter probably birds migrating through Colorado River delta. Exact chronology of migration masked by large number of wintering birds and roll-over of populations through migration corridor. Start of migration from southern wintering range presumed to be March-April; latest from Baja 28 April, but several areas with Jun records, presumably oversummering birds. Migration occurs chiefly late March through early April in Sonora, Mexico (latest 19 May. Present in southern California through late April, some lingering to mid-May. Consistent late April peak in numbers recorded at 3 central California coastal sites. No spring movement noted farther north in California at Humboldt Bay. In Oregon and Washington, peak passage extends to early May, but use of coastal sites sporadic; little use of south Puget Sound in spring but common in northern portion. Along coast of British Columbia, peak migration reported late April and early May (variable by location); beginning February large numbers of wintering birds vacate some areas. In se. Alaska (Yakutat), numbers, though small (100s), peaked 30 April-5 May. At same site in 1980 major passage noted on only a single day (4 May) with 92% of 257 birds passing 05:00-08:00 h. At principal spring staging site in Prince William Sound, birds arrive beginning fourth week of April; peak numbers recorded first week of May with last birds noted third week of May. Just west in Kachemak Bay first arrival 27 April-5 May with peak numbers 8-15 May (6 seasons between 1986 and 1993. Some unknown proportion of population likely bypasses Prince William Sound or turnover there very rapid as first birds recorded on Kodiak I. (1974-1993) 17 April (mean arrival 1 May, latest 9 May. Also several birds seen flying west over open ocean 50 km southeast of Kodiak I., 21-22 May. Arrival on breeding grounds also indicative of rapid passage once north of major wintering area. First arrival coastal Yukon Delta 1-5 May (1978-1980) with peak arrival 10-13 May; during extremely late spring 1982 first arrival delayed until 12 May. At site 15 km inland mean first arrival (1973-1996) on 6 May (range 29 April-17 May). Not common on northern breeding areas (Norton Sound) until mid-May into early June; first arrival 12-21 May 1982-1989 at Kotzebue.
Routes of dispersal to breeding sites unknown but presumed to be across base of Alaska Peninsula to Bristol Bay and there north along coast to w. and nw. Alaska; but up to 10 birds well inland along Yukon River at Galena 19-20 May 1986 hard to interpret. Thought earlier to arrive on Yukon Delta via inland route, "seemingly overland from southeastern Alaska", but no records to substantiate this route.
Southbound movement late June-early September, sometimes into November; route from west Alaska south along coast to Bristol Bay and across base of Alaska Peninsula to Gulf of Alaska. Few scattered records from interior Alaska July-August. Absence of major stopover or staging areas in southeast Alaska and large numbers of birds on Middleton I., Gulf of Alaska, led Gibson to speculate about trans-Gulf of Alaska migration in autumn. Two observed migrating 9 km offshore of Cape Fairfield in n. Gulf of Alaska on 15 August 2000. Large numbers using Prince William Sound may also bypass southeast Alaska en route to more temperate portion of wintering range. Variation in numbers reported from wintering sites suggests seasonal movement, especially November-February.
Failed breeders leave nesting areas mid-June followed by successful breeders (first females then males) and then juveniles; most begin with shift from vegetated to nonvegetated intertidal, some to inland streams and lakes, before actual flight south. Movement by all classes fairly deliberate with timing dependent on annual variation in breeding success. North of major breeding area, birds reported flocking by mid-July with drop in numbers by late July; juveniles rare by mid-August. On central Yukon Delta, flocks of adults form early to mid-June (40-75 birds/flock common); most gone by early July in years of poor reproduction but present in numbers into early July l in good years. Juveniles common into mid-August, latest usually into mid-September. Farther south in Bristol Bay common in flocks of hundreds into late August and on Alaska Peninsula adults present into late July and juveniles thereafter into late August.
Southward movement at 3 British Columbia sites (Queen Charlotte Is., Strait of Georgia, Fraser River delta) begins late June with increasing numbers reported into October. Juveniles noted first week of August and by early September outnumbered adults. At all sites numbers decreased in mid-winter as birds departed areas. In Washington and Oregon, similar migration chronology reported with migrants common by mid-July; first juveniles 6-17 August. In northern and central California migrants arrive early July through early October, most August; first juveniles reported 20 August. Like more northerly sites (see above), mid-winter drop(s) in numbers detected. Arrival southern California not until mid-July with peak about early September. Earliest arrival Baja California reported 10 July; information on migration chronology elsewhere in Mexico sketchy, but migration mainly in September in Sonora (earliest 3 September).
Numerous reported drops and then increases in numbers throughout winter range during various periods from December to February imply more than local movement but scale and extent unknown. Could be related to seasonal changes in prey.
Gregarious in migration in flocks of a few individuals to several hundred; migration probably diurnal at temperate latitudes with birds roosting at night along rocky coast. Primarily associates with Surfbird (considered obligate associate, but also Rock Sandpiper, Ruddy Turnstone, and Whimbrel (Numenius phaeopus). Large numbers of northbound migrants reported early May well offshore of California, being most common midday; spring migrants also observed in Gulf of Alaska, well offshore of east Kodiak I., Alaska, flying near the surface. Pair of fall migrants in northern Gulf of Alaska observed closer to shore (9 km) during day, flying 5 m above ocean surface. Little else known about altitude and speed of migration, methods of orientation, response to weather (but see Habitat, below), or degree of flocking and flight formation.
Control And Physiology
Spring migrants in Prince William Sound, Alaska, significantly heavier than turnstones in all other seasons (males 9% heavier than in winter; females, 16%). Eight birds (4 males, 4 females) collected May 1995 on Montague I., Alaska, had fat indices of 12.1-25.6% (lipid mass as percentage of fresh mass) and values of 0.58-1.38 for quantity represented by lipid mass divided by lean dry mass. Not known how long these birds had been on Montague I. nor how quickly they would have departed to breeding grounds, which might be from 500 to 1,150 km distant. Such fat levels ample to complete migration, suggesting extra reserves used for maintenance upon arrival and/or reproduction. First arrival on central Yukon Delta breeding grounds correlated with temperature (first day temperature more than 10°C).
Thanks to Handel, Colleen M. and Robert E. Gill. 2001. Black Turnstone (Arenaria melanocephala), The Birds of North America Online (A. Poole, Ed.). species no. 585