We got a nice, long look at Mom on Tuesday, which led to a lot of worried questions about her appearance. What was that dark mark beneath her chin? What’s going on with her face? Is she going to leave her territory? Here’s what we know.
What’s going on with Mom’s face?
In a word: Blackflies. John Howe and Neil Rettig captured several flies from Red-tailed Hawks near Neil’s home in Prairie Du Chien, Wisconsin. A professor at Clemson University identified them as Simulium Meridionale, a notorious pest of birds and mammals.
What do we know about S. Meridionale? The species produces two generations or more in a year. Females can travel up to 18 miles/30 km to take a blood meal and have been reported at heights of nearly a mile above ground. They probably deposit their eggs in running water. At our latitude, larvae hatch within a month after ice-out, usually by early May. Depending on water temperatures, pupation occurs 18 to 25 days later and adults emerge not long after that. Females require a blood meal to provide the protein necessary for egg development. Males do not take a blood meal.
Adults in our region of the Driftless are on the wing from May to October, representing at least four generations. The last generation lays eggs that suspend under the ice until the following spring. While black fly numbers will diminish as summer goes on, they won’t entirely go away.
What is that dark mark beneath Mom’s chin?
S. Meridionale females feed on blood and skin. The dark mark beneath Mom’s chin is a combination of scabs and dried blood stains caused by biting flies and scratching.
Watchers know we haven’t seen much of our eagles. They are probably spending as much time as they can on the wing and in areas with fewer flies, including open, windy areas and (possibly) sheltered areas near the ground. Based on what we know, S. Meridionale prefers to feed in the low canopy, which could make hidden low spots attractive.
Could the bites kill them?
It’s extremely unlikely. All of our eagles are healthy adults. They live in well-established territories with ample food supplies and don’t have fledglings to care for. Having said that, S. Meridionale deaths have been recorded in adult chickens. We’re doing our best to follow them remotely and we have a lot of eyes on them in Decorah. At his point, all four adults are healthy enough that we couldn’t capture them on the ground – a very good sign!
Death may be caused by exsanguination (blood loss) and/or a parasitic alveolate called a Leucocytozoon. Click here to learn more about them.
Will the eagles abandon their territories?
To us human-types, the situation looks intolerable. Young are abandoning their nests early and adults are suffering from painful bites. Their responses – scratching and twitching – don’t seem to do much to get rid of the flies. Why wouldn’t they leave for an area with less flies?
Let’s consider it from an eagle’s point of view. Blackflies lay their eggs in cold running water, which means that any territory with an ample supply of fish will most likely have at least some blackflies. Abandoning a known good territory in search of an unknown territory carries a lot of risk. An eagle will either need to drive off its counterpart from an existing territorial pair or pioneer a new territory and attract a new mate. Attacking an established pair can result in serious injury and/or immediate death. Pioneering a new territory is also risky. Our eagles know their territories. There are no guarantees that a new territory would be better than or as good as their current territory, and they wouldn’t have an established mate to help them learn the ropes.
Our answer is a cautious ‘No’, but we’ll be consulting our features database when the eagles start working on their nests again this fall.
What are you going to DO about it?
We have two options: preventing hatch and controlling flies at the nest.
The Great Spirit Bluff falcons and the Wisconsin kestrels both have the entire Mississippi River at their doorstep, which makes preventing hatch pretty tough. The steps that Laura took to control flies worked very well this year (you can read about them here) and we’ll be adopting them at GSB, with a few changes.
We might look at options to prevent or decrease hatch in Decorah and at Decorah North. Treating streams with BTI helped control flies at the Necedah Wildlife Refuge in 2010 and 2011. If we go that route, we’ll need to talk with the city of Decorah, the Iowa DNR, and blackfly control experts before we act. We’re also considering traps in the area of the nest. Female blackflies dial in on C02, which means we could set dry ice traps to draw flies away from our eaglets.
Followers are asking about dragonflies, bats, purple martins, and other means of bio-controlling insects. For a whole lot of reasons (see Did you know?) we would prefer a natural solution. We’re looking into natural controls, but we need to make sure that their lifecycle and habitat requirements are appropriate to the areas we are trying to protect.
In short: our eagles are unlikely to die or leave their territories because of the blackflies. We’ve identified at least one species of blackfly and are taking steps to protect our eagles and falcons, although the problem is complex and unlikely to be solved by one silver bullet solution at our eagle nests. We’ll be documenting and sharing successes and failures with other bird people, since bald eagles, peregrine falcons, kestrels, and red-tailed hawks are not the only bird species impacted by black flies.
Thanks for caring, watching, and learning with us – and please cross your fingers, talons, or whatever you have for drier weather!
Did you know?
Blackflies are a problem in their adult stage, but beneficial in their larval stage. Trout (and other fish) eat blackfly larvae, although studies (and opinions) differ about their importance as a food source. Like trout, blackflies benefited from the Clean Water Act, since reduced pollution means more habitat for both species (and many others). I don’t like blackflies, but find the physical and ethical challenges of dealing with them quite fascinating.
- H. Adler, Peter & Currie, Douglas & Monty Wood, D. (2004). The Black Flies (Simuliidae) of North America.
- Laura Johnson and Neil Rettig, personal communication.