Whooping Crane Eastern Partnership logo
Non-profit organizations, individuals and government agencies joining forces to bring a migratory population of whooping cranes back to eastern North America


Operation Migration Crane Camera logo



Whooping Crane Reporting Website logo


Visit with us!


Facebook logo


Flickr icon


YouTube Icon


Twitter Icon



Whooping Crane Nest Productivity Studies

Black Fly Suppression Study – Bti Treatments


Whooping crane eggs covered with black flies.

Black flies on whooping crane eggs.

Photo by USFWS; Richard Urbanek

To test the hypothesis that black flies may be partly responsible for whooping crane nest abandonments, WCEP’s Research and Science Team recommended a 2-year black fly suppression study.


Treating black fly breeding (larval) sites with Bacillus thuringiensis israelensis (Bti), a biological control agent, is the most common, environmentally safe way to reduce adult black fly numbers.   


The black fly control study began in 2009 when researchers began sampling to pinpoint potential black fly breeding sites within 6 miles of Necedah National Wildlife Refuge.  Sampling continued through 2010 and provided the information needed to identify specific locations for treatment and also helped determine that the ideal time for Bti application is in late March to early April.  The two primary black fly species of concern were identified: Simulium annulus and S. johannseni.  On Necedah NWR itself, black fly breeding sites were not found or were so small that treatment was not necessary.  Specific breeding sites on the Yellow River, Lemonweir River, South Branch of the Yellow River, and Cranberry Creek were found and were treated with Bti in 2012.  Larval populations on Beaver Creek and Necedah NWR were too small to warrant treatment.  Black fly larval sites in the Yellow River were also treated in 2011.


Before any sites were treated in 2011 and 2012, pretreatment population assessments were conducted to determine if enough larvae were present to warrant treatment.  The treatments followed  requirements under all permits, including the new “General Permit to discharge under the Wisconsin Pollutant Discharge Elimination System (WPDES)” granted by the State of Wisconsin Department of Natural Resources.


Bti Treatments


2010 – A trial application of Bti at one site on the Yellow River demonstrated the successful potential to suppress populations of two target black fly species.  These data helped determine both practicality of treatment and demonstrated the lack of impact of treatment on non-target species.  Based on the results of this trial, WCEP decided to conduct a 2-year refuge-wide black fly suppression study.


2011 – Researchers applied Bti at selected sites in the Yellow River in early April.  Each site received a one-time application of Bti.  Follow-up assessments found that the treatments effectively reduced black fly numbers during the whooping crane nesting season.


2012 – Researchers applied Bti at selected sites on the Yellow River, Lemonweir River, South Branch of the Yellow River, and Cranberry Creek during mid-late March.  Beaver Creek and Necedah NWR had black fly populations that were too small to warrant treatment. Each site received a one-time application of Bti. Follow-up assessments are on-going but results so far indicate that the Bti treatments successfully reduced black fly numbers.


Determining Bti Treatment Effects

Adult Black Fly Numbers


Researchers are using several assessment techniques to determine if the Bti effectively reduced black numbers:

Seven carbon-dioxide traps have been placed at the same sites on the Necedah NWR that were used in 2009 and 2011.


1. Carbon-dioxide traps, designed to attract female biting flies, help estimate adult black fly numbers.


2. At four carbon-dioxide traps, artificial nests were created with a plastic whooping crane decoy and a plaster-filled whooping crane egg.  The white bird and oil on the whooping crane egg are attractants to black flies.


3. Glue boards are set out along with decoy cranes, for five minutes, at recently abandoned nests and at nests where eggs recently hatched.


4. Broken eggs, along with black flies entrapped in the contents of the eggs, are collected from abandoned nests.


Whooping Crane Nesting Success

Researchers are using airplanes, augmented by observations from the ground, to monitor whooping cranes nesting in and around Necedah NWR, a 3,000 square kilometer area.  During twice-daily flights (weather permitting) new nests are located and known nests are observed to see if the pairs remain on the nest, if and when the pairs lay eggs, and if and when eggs hatch.  The flights allow close nest monitoring, even with the most remote nests, while ensuring that nest monitoring does not disturb nesting pairs and is not a factor in nest abandonment.   See the daily nest monitoring results.


The suppression program is a temporary measure to reduce black fly populations for experimental purposes only. Treated areas will recolonize with black flies in subsequent years and are expected to return to original population levels.  Reducing black fly numbers and monitoring nest success will help us evaluate whether black fly abundance affects nesting success and to what degree. It will also help us to identify other factors, like winter habitat conditions and predation,that may be important to nest success.  WCEP’s ultimate goal is a self-sustaining population of whooping cranes.  To achieve that goal, we must ensure that the whooping cranes we are releasing as part of the reintroduction project can reproduce.  The black fly suppression study will provide answers to help us achieve that goal.


Solving the Current Challenge: Working for Successful Whooping Crane Nesting in Wisconsin - A Summary of WCEP's ongoing research to ensure a self-sustaining population of whooping cranes.