Nature Of Migration In The Species
Intermediate- to long-distance migrant. One banded male breeding on Little Pelican I., Leech Lake (47°079N, 97°229W in n.-central Minnesota later observed in September in Guyana, South America.
Individuals of all North American populations migrate, some singly, others in small groups. Species migrates on a broad front throughout the Americas, preferring inland freshwater habitats but also found in small numbers along edges of coastal estuaries and even on ocean jetties. In Great Plains, uses any water available for secondary stopover sites. Females winter significantly farther north than males (n = 51 females, 43 males. Adults migrate first, followed by juveniles; females typically precede males. Some evidence that males occasionally migrate with young.
Timing And Routes Of Migration
Northward migration begins in March and continues to early June. Birds begin departing Surinam early March and are rare or absent along the coast by June. Latest date of spring departure in Peru is 25 April, in Brazil 23 April, in Paraguay 28 March. Migrants pass through central Venezuela late April-late May (maximum daily count in mid-May was 5. Costa Rica early April-late May.
Arrives central Texas late March-late May (extremes: February 20, June 14), Florida mid-March-late April (peak: third week in April; in S. Carolina, first present early April. In Colorado, arrives in lowlands beginning mid-April and in mountains late May; in Missouri, last week in April, with peak in early May; in Ohio, second or third week in April, with peak 28 April-20 May and small numbers passing along Lake Erie until 7 June.
Arrival times in north-central Minnesota (n = 6 year) vary according to experience and sex; experienced females (n = 64) arrive significantly earlier than other groups (mean 15 May), experienced males (n = 86) and inexperienced females (n = 65) arrive at similar dates (mean 19-21 May), and inexperienced males (n = 75) arrive at significantly later dates (mean 29 May). In Pacific Northwest, arrive from last week in April (Oregon) to last week in May (Washington) (range 27 April-29 May; in British Columbia, arrival begins late April and peaks mid-May in south and late May in north. Earliest recorded arrival for Alberta (Stony Plain) was 22 April, for Saskatchewan (Indian Head) 3 May, for Manitoba (Killarney) 22 April, for Quebec (Montreal) 26 April, for Alaska (Kuskokwim River) 12 May.
Begins early July; adults leave breeding grounds first, followed by juveniles. As with most shorebirds, females typically depart before males. Eastern populations thought to migrate southeast along Atlantic states, although some may use a direct transoceanic passage from New England to the eastern Neotropics.
Flocking begins in British Columbia mid-July; peak migration mid-August through October. Most birds have left Alberta by first week in Septemberr; latest departure mid-October. Latest recorded date of departure for Alaska (Kenai River) was 14 November, for Saskatchewan (Eastend) 10 September, for Manitoba (Killarney) 18 October, and for Quebec (Quebec City) 12 October.
In Pacific Northwest, departures late July-early October, peak mid-August; in north-central Minnesota, 21 May-6 August, peak 25 June-23 July. In Wisconsin, departures begin late July, and by 15 September most individuals have left; no birds present after 15 October. In Missouri, migrants begin joining previously breeding local birds in August, and most birds are gone by late September. In Ohio, departure begins 12 July-18 July, peaks 25 July-25 August, and continues until late October-early November. In central Texas, departs mid-July-mid-October (extremes: 27 June, 22 November); in Florida, late June to third week in October.
Arrival on wintering grounds in Florida mid-July; in s. California, early August; in Mexico, Costa Rica, and Panama, early August through October. In Surinam, arrives first week of July. Earliest recorded arrival date for Venezuela (Curaçao) 27 July, for Ecuador (Guainche) 27 August, and for Peru (Inquitos) 1 August.
At Norman, Oklahoma (n = 3 yr), a total of 68 individuals spotted during spring migration (19 April-31 May), only 9 during southward migration (12 July-12 September. The observation that fewer fall migrants than spring migrants use an interior North American route through Mississippi Valley and Great Plains may reflect fewer stopovers during fall migration, and/or use of more coastal routes, or both.
Usually migrates singly in spring and singly or in small groups in fall. Migrates day and night. Weather conditions determine departure from breeding grounds. In north-central Minnesota, fall migrants depart when high-pressure fronts and northwest winds arrive. Halts migration if rainy-stormy weather or strong head winds. Known to cross large bodies of water, such as Gulf of Mexico, Atlantic Ocean, Pacific Ocean, and Caribbean Sea.
Control And Physiology
Among captive birds, migratory restlessness increases during high-pressure fronts in late summer and fall. Adults and young store fat reserves just before departure in summer. Weight gain (more than 100%) also recorded in summer for birds in captivity (n = 10). Birds migrate southward while local prey are still abundant on breeding grounds. No evidence of how the degree of fat deposition affects length of stay at stopover sites.
In north-central Minnesota, both cessation of breeding and initiation of molt appear to be related to photoperiod. As days begin to shorten in late June, vocalizations change and breeding halts. Latest nest completion date in 21 yr was 9 July. Since egg-laying lasts usually 4-5 day and the prelaying ovule growth period lasts at least 3 days, initiation of egg development ends by 1 July, only 10 days after summer solstice. Thus, hormonal promotion of reproduction appears to shut down rapidly with decreasing day length, although precise timing of this shutdown probably is moderated by social behavior. In high-montane areas of California, where onset of spring is sometimes very late because of heavy snowfall, and where day length does not vary as greatly as in north-central Minnesota, endocrine control of breeding seems liberated from day length because chicks are often found in early to mid-August, indicating that some laying occurs mid- to late July.
Thanks to Reed, J. Michael, Lewis W. Oring and Elizabeth M. Gray. 2013. Spotted Sandpiper (Actitis macularius), The Birds of North America Online (A. Poole, Ed.). species no.289