May Nature Almanac: Enticing Avocets
by Scott Severs
May 2021
Each spring flocks of shorebirds traveling through eastern portions of Boulder County search for places to stop over to refuel before continuing northward to breeding areas on the arctic tundra. Lakes, marshes, and mud flats harbor crustaceans and insect larvae—important food for hungry birds that need to replenish energy reserves for egg production. Other shorebirds remain here for the summer, setting up territories in the few suitable habitats that remain. One such species is the appealing American Avocet.
Avocets often nest on exposed mud flats, where they use alarm cries, broken wing acts, and confrontation to deter predators. Photo by Stephen Jones
Unquestionably beautiful, avocets are easy to identify. They have black and white wings and, during the breeding season, a rusty wash on the head and neck. Their long bills curve upward (strongly so in females). To feed, they sweep their bills from side to side through the water. Upon sensing prey by touch, avocets pause to snap up the tiny shrimp or insect. Stilt-like blue legs with slightly webbed toes allow avocets to forage in deeper water than other shorebirds.
Avocets begin the breeding season (which lasts from April through June) with an intricate courtship ritual. The female adopts a rigid posture while the male preens beside her, hops on her back for copulation, and then hops beside her again and stretches a wing across her back. The pair then cross their bills like sabers. Courtship rituals like these help to strengthen the pair bond.
Avocet nests, small depressions on the ground called scrapes, are located on the sandbars and shorelines of lakes or mud flats. If rising water levels threaten the nest, the adults will prop it up with debris. Both sexes incubate three to four blotchy olive-brown eggs over a period of about 25 days. The young, like most shorebirds, are precocial—meaning they can move about and forage for themselves soon after hatching.
Ground-nesting species are more likely than others to be precocial because while marauding predators would make short order of a nest full of naked nestlings, precocial young may be able to escape. Any animal attempting to prey upon an avocet chick will first have to deal with a barrage of attacks from the adults and other avocets from nearby nests. Additionally, the young are superbly camouflaged to blend with the gravelly substrate. Their first flights occur about a month after hatching.
The "incubating" avocet in this photo is simply trying to distract the potential predator (the photographer) away from the actual nest, which is situated on a more exposed mud flat. Photo by Stephen Jones.
Superior resident Peter Ruprecht and a team of citizen naturalists have been working with Boulder County Parks and Open Space Senior Wildlife Biologist Susan Spaulding to protect a nesting population of avocets from flooding at a local reservoir that has enticing mudflats for nesting. Water storage for irrigation can jeopardize new nests, so Peter coordinates with Susan, letting her know when to manipulate the water levels to maximize the benefit for nesting avocets. Susan notes that “…water rights issues must be carefully considered.” The volunteers also report numbers of other declining species such as blue-winged teal and Wilson’s phalarope.
The avocets at this reservoir have responded with multiple nesting attempts over the last two springs. Unfortunately, the nests have been unsuccessful to this point due to predation of the eggs, likely by coyotes. It can be challenging to conserve and manage wildlife in a manmade setting such as a reservoir when surrounding habitat is scarce and reservoirs are attractive to both predator and prey. Susan sums it up “With human alteration of our environment, species that depend on ephemeral habitat types are experiencing declines, as we know. This is why our department has focused on coordination towards avocet conservation.”
Avocet populations, like those of other waterbirds, suffer from lost wetland habitat, development of shorelines, and pollution. Despite their vigorous attempts to defend nest sites from predators, continued harassment from uncontrolled pet dogs have caused whole colonies of avocets to abandon eggs and young. These factors pushed avocets out of the eastern United States. The remaining strongholds of the species in the west continue to shrink. Luckily, some avocets continue to nest in eastern Boulder County. They prove wonderful subjects for observation, but please take precautions to be non-intrusive.
Additional May events
The season’s first dragonflies, including dot-winged baskettails and common green garners, appear at ponds and marshes.
White-crowned Sparrows and American Pipits transition uphill to the sub-alpine and alpine.
Scarlet globemallow, spiderwort, and milk vetch begin to pop on local prairies.
Common Poorwills begin to sing on moonlit nights among the trees of ponderosa pine woodlands.
Male Woodhouse’s toads broadcast their calls (a long, monotonal "waahh") to prospective mates in marshy shallows.
Scott Severs is a wildlife biologist with the Natural Resources Division of the City of Longmont.