Home
Field Notes
 
U.S. Fish & Wildlife Service
Field Notes Entry   
MERCED NWR: Tricolored Blackbirds Find a Home at Merced National Wildlife Refuge
California-Nevada Offices , April 28, 2015
Print Friendly Version
A flock of 8,000-10,000 tricolored blackbirds have established a nesting colony this spring at the Merced National Wildlife Refuge.
A flock of 8,000-10,000 tricolored blackbirds have established a nesting colony this spring at the Merced National Wildlife Refuge. - Photo Credit: Rick Lewis
Male tricolored blackbirds in a stand of mustard at the Merced National Wildlife Refuge.  The birds have been present within the San Luis NWR complex every winter from 1990 to 2015, and have established nesting colonies in most years.
Male tricolored blackbirds in a stand of mustard at the Merced National Wildlife Refuge. The birds have been present within the San Luis NWR complex every winter from 1990 to 2015, and have established nesting colonies in most years. - Photo Credit: USFWS

By Madeline Yancey

 

The tricolored blackbird is a species in trouble. The nearly-endemic colonial-nesting California songbird once numbered about three million birds in the mid-1900s, but the population has declined to around 145,000 as of the most recent survey conducted in 2014.

Loss of habitat is the primary cause. Vast acres of dense cattail tule marshes for nesting and nearby fields of upland grasslands full of grasshoppers and butterflies for foraging have been lost to agricultural and urban development and, more recently, to the drought. As North America’s most colonial songbird, tricolored blackbirds gather into huge flocks numbering tens of thousands of individual birds during the nesting season. Loss of habitat has forced the blackbirds to nest in less desirable habitats, such as agricultural fields of triticale wheat. The problem arises for the birds when it is time to harvest the wheat and the young have not yet left the nest. Harvesting machines destroy the nests and the young birds that have not fledged, resulting in the loss of an entire generation. This scenario occurs repeatedly throughout California each nesting season.

At the Merced National Wildlife Refuge (a unit of the San Luis NWR Complex) in Merced County, Calif., the Refuge and its staff are doing what they do best – providing habitat for wildlife. This has resulted in a flock of 8,000 to 10,000 tricolored blackbirds moving in.

The colony of birds showed up around the end of March and quickly got to work carrying nesting materials into a refuge crop field that last summer grew a crop of corn to feed wintering arctic-nesting geese and sandhill cranes. The field was then allowed to go fallow and proceeded to grow a robust stand of mixed herbaceous forbs including black mustard and milk thistle. While not the tricolored’s preferred nesting habitat of dense emergent wetland vegetation, this plant community is well-suited as the stems of the four-foot-tall plants are robust enough to support the birds’ nests and the thistles seem to provide protection against potential predators.

In addition to nesting habitat, the birds need productive areas to forage for insects – a high-protein food needed for females to lay eggs and also by young growing birds. The colony is finding foraging habitat on the refuge as well, as hundreds of females have been observed feeding on butterflies and other insects in refuge uplands north of their nesting site.

The noisy frenetic activity of courting and nest-building in early April has subsided and the tricolored colony is now eerily quiet. UC Davis tricolored blackbird researcher, Bob Meese, says that’s because the birds are now sitting on eggs, eggs that will hatch in a short 10 to 12 days.

The San Luis NWR complex of refuges has been providing habitat for tricolored blackbirds for decades. The birds have been present on these refuges every winter from 1990 to present day, and have established nesting colonies in most years. Colony size has ranged from 12,500 to 65,000 breeding birds. Since 2005, however, nesting colonies have only occurred at the Merced Refuge. The Refuge’s practice of planting farm fields to corn and winter wheat then letting the fields go fallow to grow suitable pioneer plant species has provided the tricolored blackbird with critical nesting and foraging habitat at a time when the species is faced with an increasingly difficult agricultural and urban landscape.

Shortly after the young tricoloreds hatch amongst the mustard and milk thistle, a team including refuge staff will carry out activities to determine nest density within the colony and production (of young). This will include trapping and banding individual birds. Information learned will help biologists and others provide essential habitat needed by the species if it’s to remain a living part of California’s wildlife heritage.

- fws - 

Madeline Yancey is a visitor services specialist at San Luis National Wildlife Refuge Complex in Los Banos, California.


Contact Info: Jack Sparks, 209-826-3508, jack_sparks@fws.gov
Find a Field Notes Entry

Search by keyword

Search by State




Search by Region


US Fish and Wildlife Service footer