Distribution: Distribution of the American avocet, Recurvirostra americana, is highly dependent on suitable local habitat, making the breeding range somewhat spotty and localized. The American avocet breeds in North America in the western and west-central United States, the Gulf and Atlantic coasts, and in south-central Canada.
Most breeding in Utah occurs on mud flats in the wetlands associated with the Great Salt Lake, Utah Lake, the Bear and Malad Rivers in northern Utah, the Logan and Little Bear River in Cache Valley (Hayward et al. 1976), the Bear River Migratory Bird Refuge in Box Elder County (Roy 1998), and the Ouray National Wildlife Refuge and other reservoirs in Uintah County (Sjostrum 1998). Some breeding does occur in Rich County on the mud flats surrounding Bear Lake (Sjostrum 1998), at Fish Springs National Wildlife Refuge in Juab County (Banta 1998), in the wetlands surrounding Clear Lake Waterfowl Management Area (WMA) near Delta in Millard County (Zubeck 1998), at Blue Lake WMA south of Wendover in Tooele County, and at Desert Lake WMA south of Price in Grand County (McIvor 1998).
The avocet winters primarily from coastal California south through Mexico to northeastern Guatemala. Wintering also occurs along the southeastern coast of the United States and along the Gulf Coast. A small number of avocets sometimes winter within the northern breeding areas in Utah, Nevada, and Oregon (Robinson et al. 1997, Hayward et al. 1976).
Ecology: The primary foods for the American avocet are invertebrates of the water column and sediment, including water boatmen (Hemiptera, Corixidae), beetle larvae (Coleoptera), fly larvae (Diptera), and particularly midges (Chironomidae); terrestrial invertebrates consumed include grasshoppers, caterpillars, and spiders. Other foods include small fish and seeds, especially sago pondweed and bulrushes. In the more saline wetlands in Utah, avocets also feed on brine shrimp and brine flies. Avocets forage while wading in water depths up to 15 to 20 cm and while swimming in depths up to 25 cm. The characteristic of the substrate is an important factor in determining the foraging method (i.e., pecking or scything). Avocets have three visual feeding methods: pecking, plunging, and snatching; and six tactile feeding methods: bill pursuit, filtering, scraping, single scything (bill is held open slightly at the muddy substrate surface and moved from one side to the other), multiple scything, and dabble scything. Scything has been noted as the hallmark method. Avocets have also been observed foraging cooperatively in close groups using the multiple scything method, probably feeding on small fish (Robinson et al. 1997).
The birds arrive in Utah in late March. Pair formation seems to occur before and during migration, and is usually complete before arrival at a breeding site. The nesting site is selected jointly after nest-searching and scraping displays. Selected sites are usually in very sparse vegetation in an area affording an unobstructed view. Nests are located on islands when available, on dikes, or other areas associated with the water's edge. The nest is scraped into the substrate with the breast and feet by either sex, and small pieces of lining material are added throughout the incubation period. Nest diameter averages 146 mm, and depth 36 mm. Eggs are pyriform to long pyriform shaped, and average 5.0 cm in length and 3.4 cm in breadth. Three to four eggs are laid, and incubation onset is dependent on the local ambient temperature (in moderate temperatures incubation begins with the penultimate egg; in very warm weather, the eggs will begin to develop without incubation, and the birds may have to cool the eggs by wetting the breast and laying on the eggs). Incubation period is measured from date of first egg laid to date first egg hatched, and averages 26.4 days. Incubation period decreases over the season in response to increasing temperatures. Both sexes incubate the eggs alternating throughout the day and night. Eggs will usually hatch over 1-2 days. Chicks are hatched precocial, downy, and able to feed themselves. Young birds will remain in the nest for 24 hrs after last chick is hatched if undisturbed. The adults will then lead the chicks to a brood nursery area with shallow water and sufficient vegetation for cover. Downy chicks are attended by both parents, but as the young birds obtain their juvenile plumage, one or both parents may leave. After about 27 days, the young avocets are capable of sustained flight, and spend their days in flocks with other fledglings and adults. They will remain in these flocks for 1 to 3 weeks, and then fly south in small groups with other juveniles. American avocets leave Utah for wintering grounds beginning in August and through September. Birds have been observed at Bear River Refuge as late as mid November (Roy 1998, Robinson et al. 1997, Sordahl 1996).
Habitat Requirements: American avocets breed in fairly specific habitat regimes. Their somewhat spotty breeding range is indicative that breeding occurs in specific suitable areas. Nesting occurs in areas with salt ponds, potholes, or shallow alkaline wetlands. It also occurs in some mud flats of inland lakes and impoundments and evaporation ponds. The alkaline wetlands are characterized by the presence of common cattail (Typha latifolia), bulrushes (Scirpus spp.), and sedges (Carex spp.); however, most time is spent in more open areas with no vegetation or with sparse vegetation consisting of glasswort (Salicornia spp.), saltgrass (Distichlis spp.), or greasewood (Sarcobatus spp.). The birds feed in open water 0-20 cm deep, and sometimes deeper. The nests are usually built on islands or dikes with sparse vegetation. In desert wetlands, especially in Utah, avocets nest along the lake shoreline among scattered patches of vegetation, along barren mud flats, or up on small patches of vegetation over water. Wintering habitats include intertidal mud flats and brackish-water impoundments (Robinson et al. 1997).