In July, bird watchers know it is time to start looking for shorebirds here in Central Texas. Shorebirds are part of the bird order Charadriiformes, known for foraging in both coastal and freshwater habitats. They are probing for aquatic invertebrates along sandy and rocky shorelines of rivers, lakes and ponds, mudflats, irrigated agricultural fields, turf farms, moist short grasslands and marshy areas. Some with longer bills and legs will wade into water of various depths for prey. Some will pick insects from the water’s surface. The species of expected shorebirds range in size from sparrow-sized sandpipers to dove-sized dowitchers and long-legged waders like avocets and stilts.
Typically, most migratory shorebirds move through Austin from March to May, with very few seen in June. As July progresses, the adults of twenty-two species are probable, arriving from their summer breeding grounds. They are on their return journeys to wintering grounds along the coast or down into Central and South America. Austin has one very reliable spot for them, the Hornsby Bend Bird Observatory, which has a variety of habitats to meet their needs.
Seeing Spots
Most shorebirds are well camouflaged to blend in with their surroundings and are daunting to identify. The Spotted Sandpiper is different. It has behavioral clues, along with lots of spots in breeding plumage that make it stand out from the crowd.
The Spotted Sandpiper is the most widespread sandpiper in North America. In the breeding season, it can be found from the southern edge of the Arctic down to the states from California to Kansas across to Virginia. It winters mainly in Central and South America, with some staying in the Gulf Coast states. We are lucky to have them wintering in the lower 2/3 of Texas, both inland and at the coast. Its generalist diet and adaptability to various habitats from shoreline to urban ponds help explain its wide range. They’ll even nest in arid areas as long as there is water close by.
During the breeding season, the Spotted Sandpiper has large dark spots on its bright white breast and belly, with the female’s spots larger and going further down the belly. Its back is brown, bill pinkish, legs greenish-yellow, and it’s about 7.5 inches in length. In non-breeding plumage, its spots fade, with a few sometimes visible on the flanks. The leg color fades, and the sides of the breast are brownish. Juveniles look somewhat similar to non-breeding adults but initially have pale tips to their feathers and strong markings on their upperparts, which wear off in the winter. All birds look chunky with short necks and short legs.
Distinctive Foraging Behavior and Flight Pattern
The Spotted Sandpiper has a horizontal posture but bends forward in a crouch with its tail in the air while foraging. It also teeters back and forth, even when standing still. (Thirty minutes after hatching, chicks show this behavior. The reason for this trait is unknown.)
When Spotted Sandpipers fly, they make a peet-weet-weet call of varying length. They have very fast, shallow wing beats, and the shallow wing beats allow them to fly close to the water. In flight, look for a white stripe in the upper brown wing, which helps separate this species from the similar Solitary Sandpiper with which it is often confused.
Polyandry
The Spotted Sandpiper is one of the few bird species that exhibit polyandry (literally meaning “many husbands” or “many men”). The male and female have reversed sex roles so that the male is responsible for incubation and raising the young, while the female claims and defends a territory and courts males. The females winter further north than the males, allowing them to reach the breeding grounds faster. Female-to-female defense of territories can lead to serious harm, such as broken legs and damaged wings and eyes. This may occur when the sex ratio is skewed so that females outnumber males, such as at the start of the breeding season. When more males are available than females, male-to-male fighting may occur, but serious injuries are less likely to occur.
Experienced older females have been known to attract as many as four males over the course of the breeding season. The males each raise a clutch, typically of four chicks. One female was observed laying five clutches with three males in 43 days! Monogamy may occur at the start of the breeding season when the female helps with incubation and brooding. When more males arrive, she competes for them, and the male assumes all parental duties. Once she is laying eggs, however, she won’t compete with other females. Observers have noted that in some areas and also in the last clutch of the breeding season, females help with the entire span of chick-raising tasks. It’s not uncommon for first-year females to be monogamous.
To offset the demands of egg formation, females are 20 to 25% larger in mass. They possibly eat empty snail shells for calcium.
Males have higher levels of circulating prolactin hormone, which apparently improves parental care. This is regulated by testosterone, which decreases when the third egg is laid, increasing prolactin just in time for the male’s incubation tasks to start…