NESTS ABANDONED

Black flies may be responsible for a high number of whooping cranes abandoning their nests in the core reintroduction area in central Wisconsin.  To test this hypothesis, the Whooping Crane Eastern Partnership (WCEP), the coalition of public and private groups that is reintroducing whooping cranes to eastern North America, has been conducting a multi-year study to examine the causes of nest abandonment.

Whooping crane eggs covered with Black flies

Abandoned Whooping crane eggs with black flies. Photo credit: Richard Urbanek, USFWS

The specific goal of this study is to temporarily remove target species of black flies from the environment and examine whooping crane nest success as a result.  Other factors that may relate to reproductive success are also being examined, including predation, food availability, and age/nesting experience of the birds in the population.

In spring 2011 and 2012, WCEP biologists conducted a two-year black fly suppression treatment to evaluate the role that black flies play in whooping crane nest abandonments.   Two rivers near Necedah National Wildlife Refuge (NWR) that were known to have significant populations of breeding black flies were treated with Bacillus thuringiensis israelensis (Bti), a naturally occurring soil bacterium used as an alternative to chemical pesticides to control insects. Bti is the most common, environmentally safe way to reduce adult black fly numbers.

Follow-up assessments found that the treatments during the two-year study significantly reduced black fly numbers during the whooping crane nesting season.  This spring, no Bti treatment was applied, allowing researchers to differentiate between the increasing experience of the nesting birds at Necedah NWR and the effect of black flies.

Twenty whooping crane pairs have initiated nests this spring so far.  Seventeen of those nests were abandoned during a four-day period, from May 4-7.  Nineteen eggs were collected from the abandoned nests. At the time of egg collection, dense clouds of black flies were observed at the nests.  Several of the collected eggs have been determined to be fertile and are currently being incubated at the International Crane Foundation. They will be used in whooping crane reintroduction efforts.

“This study is critical to guide future decisions for how to manage whooping cranes that currently nest within the area affected by black flies, as well as where else we can work to re-establish whooping cranes in Wisconsin and in the Upper Midwest,” said Jeb Barzen, Director of Field Ecology, International Crane Foundation.

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14 Comments

  1. Chris Bown May 18, 2013 5:16 pm

    Do these Black flies bother Sandhill Cranes, are Sandhills abandoning their nests? side Question if you could answer…Could they move the whooping cranes from Florida to Louisiana to give the flock a little jump start?

    • Heather Ray May 18, 2013 5:23 pm

      Sandhills (and Trumpeter swans) tend to nest a bit later, after black flies have dissipated. Now that the whooping cranes in Florida have established territories, moving them would do little. They would likely just return to Florida.

  2. Heather Ray May 18, 2013 6:00 am

    Posted on behalf of Ed Kahler:
    Black flies may be responsible for a high number of whooping cranes abandoning their nests in the core reintroduction area in central Wisconsin. ” May be responsible? I have been following OM for years. Each year the black flies drive the birds crazy and the birds abandon their nests. The problem was so bad that OM had to leave Necedah. How much proof does a person need? Causality seems to have been established.
    Then the magic bullet was found, Bti. “Follow-up assessments found that the treatments during the two-year study significantly reduced black fly numbers during the whooping crane nesting season.” “ This spring, no Bti treatment was applied, allowing researchers to differentiate between the increasing experience of the nesting birds at Necedah NWR and the effect of black flies.” “Twenty whooping crane pairs have initiated nests this spring so far. Seventeen of those nests were abandoned during a four-day period, from May 4-7. ” Now another season has been lost because the abandonment rate is 77%. I realize that the researchers are following the rules of the scientific method to ensure a high quality conclusion but, are we trying to save a species or impress our Bio 101 profs? Has the following option been considered: use Bti for the number of years needed to increase the Whooping Crane population to a point that the population is so large that Necedah is no longer needed. Then decide what to do next. The approach puts the birds first and science second, an acceptable deviation considering that the survival of a species is hanging in the balance.
    Finally, put the situation in human terms. You are in your house and trying to raise your children but you are being terrorized day and night by gangs. See, the decision is simple.

  3. Kirsten Akse May 16, 2013 9:26 pm

    Are black flies native to Wisconsin or have they been introduced? Why are there so many of them and do they effect other birds/animals?

    • Heather Ray May 17, 2013 7:49 am

      Black flies are native to Wisconsin. There are two species (of Black fliy) that specifically target birds. Simulium annulus and S. johannseni. Both of these have been found in Juneau County – the core reintroduction site. Black flies deposit eggs in fast moving water and there are two such rivers not far from the nesting areas: The Yellow River and Lemonweir River. As weather warms in the spring the black flies emerge and seek out birds to feed upon.

  4. Claire DeLand May 16, 2013 4:51 pm

    How do you go about rescuing the eggs from abandoned nests? Sounds kind of tedious . . .

    So MUCH to learn!!!!!

    Thanks, Heather!

    • Heather Ray May 17, 2013 7:42 am

      Refuge staff and project partners visit each nest, either by foot or canoe to retrieve abandoned eggs.

  5. Karen Anne May 16, 2013 11:26 am

    I’ve forgotten – is this the new area where there are supposed to be fewer blackflies, or the previous area?

    • Heather Ray May 16, 2013 12:03 pm

      its the previous area Karen.

  6. Chris Cranefan May 15, 2013 9:10 pm

    If whooper pairs lose nests due to blackflies, do they relocate in later years? Or are they locked in to breed in a region close to where they grew up?

    • Heather Ray May 16, 2013 5:11 am

      Nest locations from year-to-year change to some degree but they do tend to stay within the territory they have selected. If a first nest attempt fails they may re-nest shortly afterward.

  7. Margie Tomlinson May 15, 2013 9:00 pm

    Thank Goodness they rescued the eggs! Those Black flies are real monsters! They bite humans, too, and it hurts and it’s bloody. Poor birdies, no wonder they abandoned their nests. I sure hope they will resume treatment for next year’s nesting season.

  8. Karen Anne May 15, 2013 2:31 pm

    How big a clue do they need? Is it too late for BT treatment now?

    • Heather Ray May 15, 2013 4:26 pm

      yes Karen, BTi must be applied during the larval stage of the Black flies so that they ingest the bacterium