Natural Fly Control on Rotational Grazing Silvopastures

Final report for FNC21-1281

Project Type: Farmer/Rancher
Funds awarded in 2021: $5,866.00
Projected End Date: 01/31/2023
Grant Recipient: Harmony Hills Farm
Region: North Central
State: Missouri
Project Coordinator:
Brian Keeter
Harmony Hills Farm
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Project Information

Description of operation:

Harmony Hills Farm is a 43 acre farm approximately 1 hour west of St. Louis, MO. We purchased this farm in 2019 and are a team of two farmers who live here and are working to build a multispecies silvopasture grazing system. We started grazing South Poll cattle and added Katahdin sheep in 2021. We use portable electric fencing and move the animals frequently. Depending on many factors including weather, forage available, and time of the year, the animals are rotated between twice a day and weekly. We are working to convert this property to silvopasture by planting native trees in open pasture areas and selectively removing trees from an overgrown and previously unmanaged woodland. We experienced extreme fly pressure on our cattle herd and the only remedies that we were able to locate included pesticides which we were unwilling to use on our property. One of the goals that we are working on with our local NRCS office is increasing the dung beetle population on our farm and so we sought a non-chemical alternative to fly control.


Fly pressure is responsible for millions of dollars of loss in the cattle industry through stress, blood loss, decreased grazing efficacy, reduced weight gains, and diminished milk production in mother cows.   We would like to demonstrate an easy, low labor, and low cost method of controlling those flies.  Reduced fly pressure will allow us to have healthier animals and by using lumber from the property we will increase the acres of grazable land allowing us to increase our herd size in future seasons.   

Project Objectives:
  1. Identify the appropriate number of tree swallow houses to that will be needed to maintain a healthy population of tree swallows and minimum number of flies on the farm.
  2. Harvest red cedar lumber on the farm to expand our available pasture land. The harvested lumber will provide raw material to construct tree swallow houses to be used on the farm and sold at local farmers’ market and through our website to generate an extra income source.
  3. Evaluate health of cattle utilizing tree swallows as fly control method 
  4. Share findings through organizing an on farm field day, website/social media, instructional videos


Materials and methods:

The birdhouse design that we will be using was created by Cornell University as part of a study on Tree Swallows that they conducted in 2003.  Please see the attached pdf of their design:

nest box design Cornell oct 2009 (1)

Each of the pastures that we will be sampling from averages 10-15 acres. We will be monitoring the fly population using fly paper mounted near the cattle water trough.  Numbers will be tabulated weekly on the flies that are caught on the fly paper.  

By using red cedar from the property, we will build birdhouses that will last for many years and prevent us from having to rebuild or replace them due to wood rot.  Using lumber from the property also allows us to limit outside inputs and open up an additional pasture for future grazing.

We have planned a collaboration with Earthdance Organic Farm School to host a field day during the late summer in 2022 to demonstrate our project to local farmers and apprentices.  We will have printed material available for the participants at the field day in addition to a display board with pictures documenting the progress of the project.  We will be able to utilize this display board at local farmers markets as well.  In addition to documenting this project with pictures, we will make a video showing the completed project and how to assemble the birdhouse if someone wanted to make their own.

Update mid-project:

I have had to make a small adjustment to the Cornell birdhouse design.  The original design assumes that the lumber is purchased from a retail location and has nominal measurements which do not measure true.  We milled our cedar lumber to measure exactly 1" thick instead of the standard 3/4" thickness of a 1x4 purchased retail.  This caused our birdhouse to be off by 1/2" total and so the width of the front and back of the birdhouse were both increased 1/2" to 7" from the original planned 6.5".  

We have utilized the distance measuring tool on Google Earth to plot out exactly where each of the birdhouses will be placed in the two pastures.  We are currently finishing the construction of the birdhouses and will install them in the pastures in February 2022 before the spring migration of the tree swallows.  

We removed 21 cedar trees in October 2021 to be milled into lumber.  While removing these trees opened a nice path into the woods, it hasn’t yet provided enough open space to allow for livestock grazing.  We are working closely with our local NRCS office to seed a cover crop to serve as forage for local wildlife for the next several years while we work on continuing to open the canopy enough to allow for grazing of livestock.  As we develop our silvopasture, we are selecting several large healthy trees to remain in the space we are opening to provide shade for our livestock in the future.  By removing trees individually and not with heavy machinery, we are able to maintain the health of the trees that will remain and not disturb the current ecosystem. 

Additionally, we did some testing of the fly paper setup with our cattle in the summer of 2021 to work out any kinks in that setup prior to the research we will be conducting in the summer of 2022.  I had originally proposed that we would change the fly paper weekly and we now plan to change the paper with greater frequency.  In my tests, I found that once the fly paper was filled with black flies, they attracted small birds who would get stuck to the fly paper.  In order to prevent this from happening, we found that by changing the fly paper every 1-2 days prevented the birds from being attracted to it and getting stuck.  

Final Project Update:

At the end of February 2022, we installed the tree swallow bird houses in two of our three pastures.  In pasture "A", we installed the bird houses 100' from each other.  They were also at least 100' from the tree line and a small gravel road.  In pasture "B", we did not install any bird houses.  In pasture "C", the bird houses were placed 200' apart.  The cattle are moved twice each day and they spend approximately 3 weeks in each pasture.  Each morning and each evening, we move the cattle to the next paddock and refill their water trough.  While we waited for the water to fill, we logged on a Google Sheets document the number of tree swallows that we could see flying around the cattle.  Tree swallows are a very distinct bird and have a very characteristic "dive bombing" flight pattern as they fly around the cattle eating flies.  They are very entertaining to watch!  Prior to the summer of 2022, we had not ever seen a tree swallow on our farm. 

During the paddock moves twice a day, we would also move and reset the fly paper traps and document the number of flies on each trap.  As we experienced in the summer of 2021, we discovered that our original proposed setup of fly paper next to the cattle water unfortunately attracted small birds to the flies, resulting in two birds being stuck on the fly paper.  This was very distressing to us and we worked continuously to develop a fly trap setup that allowed it to be moved easily twice a day, could fit between the water trough and the side by side vehicle with the water tank, and prevented birds from getting stuck.  We tried building a wooden frame and adding a screen of chicken wire in front of the fly paper, but determined that it significantly reduced the number of flies that were able to catch, resulting in inaccurate data.  In the end, we determined that it was best to just change the fly paper every morning so that we did not allow a build up of flies, which would look like a tempting treat to a small bird.  The fly paper was also sometimes ineffective when it was extremely rainy or windy.  Because we were unable to be completely consistent with tracking the flies on the fly paper, right from the start we added a secondary method of tracking the flies.  In reading previous research done at commercial scale cattle operations, they count the number of flies on the face and a foreleg of a select number of animals to provide an average of the herd fly pressure. 

Each morning and each evening, we logged five things on our Google Sheet - the paddock they were currently in, the number of visible tree swallows flying among the herd, the average number of face flies and foreleg flies, the number of flies on the fly paper, and the weather that day (temperature and precipitation).  

In pasture "A", where we had 12 bird houses spaced 100' apart, we observed 3 of them were habited with tree swallows.  The number of swallows that we spotted each day averaged 4.  The average number of flies on each animal when they were in pasture "A" was 12.  

In pasture "B", we had no bird houses.  There is a tree line separating it from pasture "A", but there isn't a great distance between them.  When the cattle were in pasture "B", we observed almost no tree swallows around the cattle.  I could sit at the tree line and see the tree swallows in pasture "A" to my left flying around and when I looked just a few hundred feet away to pasture "B", the tree swallows just didn't fly over to where the cattle had been moved.  The average number of flies on each animal when they were in pasture "B" was 32.  

In pasture "C", we had 8 bird houses and they were spaced 200' apart.  Pasture "C' is separated by a tree lined creek from the rest of the farm.  When the cattle were in pasture "C", we observed 6 of the 8 bird houses were habited with tree swallows.  The average number of tree swallows that we spotted each day was 8.  The average number of flies on each animal when they were in pasture "C" was 6.  


Research results and discussion:

Portable sawmill set up at the farm and milled the cedar trees into lumber.
Cattle in August 2022 with face flies, after tree swallows migrated away
Cattle in August 2022 with face flies, after tree swallows migrated away

fly paper tracking fly count in the summer of 2021

Cedar trees were cut and stacked with the grapple tool. The tree tops and limbs will be shredded and used for mulch in garden walkways this summer.

We are on track for our project as of this progress report in January 2022. We removed the cedar trees and had them milled into lumber.  We used the lumber to construct the birdhouses and are installing them into the pastures now.  We will begin monitoring fly population this spring and will track that data through the summer of 2022. 

Participation Summary
2 Farmers participating in research

Educational & Outreach Activities

1 On-farm demonstrations
3 Webinars / talks / presentations

Participation Summary:

18 Farmers participated
22 Ag professionals participated
Education/outreach description:

We have scheduled a field day for a group of local livestock farmers in collaboration with Lincoln University and the NRCS that is scheduled for September 20, 2022.  We had presentations by the NRCS on soil health, a demonstration by the small ruminant specialist from Lincoln University on using the NRCS grazing stick to track forage, and a presentation by Harmony Hills Farm on the results of this SARE project.  We also included a tour to show our rotational grazing system.  

We had two neighboring farmers interested in our project early in the spring 2022, and they purchased bird houses from us and we followed along with the activity that they observed at their bird houses through the summer.  We hosted a group of farmers from our region to share about our project and our silvopasture system.  It was an opportunity to share information not only on our tree swallow project, but our moveable electric fence system and pasture tracking map.  I shared our research at two separate events to livestock and agricultural extension specialists in Missouri.  Finally, I was asked to share my experience with a SARE Farmer/Rancher grant at a grant writing workshop for 32 participants in November 2022 sponsored by Lincoln University.  

We had a table dedicated to our tree swallow project at our farmers market booth each week, which allowed us to not only sell some of our bird houses to the public, but we were able to share about our research and about SARE with our customers and members of our community. 

Learning Outcomes

8 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Lessons Learned:

The research that we had read from Cornell University before beginning our project stated that tree swallows were territorial birds.  Our experience with observing them this summer confirms this.  When the bird houses were very close together, only a few of them were habited.  When the bird houses were spaced out, almost all of them had tree swallows take up residence.  This was a case of "less is more".  More bird houses did not equal more tree swallows and we plan to remove several of the bird houses from pasture "A" before the spring 2023 and move them to pasture "B" and continue monitoring their effectiveness in reducing fly pressure.  

In the summer of 2021, before we had installed our bird houses, we purchased 9 steers.  They arrived with a very large swarm of flies and we were never able to get on top of the problem before the frost in the fall finally gave them a reprieve.  The average number of flies on each animal was 42.  This number was consistent through each of the pastures and throughout the summer, fluctuating only when there was severe weather.  We could not have been more pleased with the benefit that the tree swallows brought to our farm in the summer of 2022.  While the birds were here, they provided an excellent option for reducing the fly pressure on our cattle.   Even comparing pasture "B", which had no bird houses and by far the most observed flies - the number of total flies on the farm while the tree swallows were present was significantly reduced from the previous summer.  

However, tree swallows are a migrating bird and they don't stay in Missouri until the frost.  At the end of July, we had a week of very severe weather.  Temperatures were consistently over 100 degrees and we had over 8" of rain.  Once the weather broke and we had a mild day, we noticed that we didn't see any tree swallows.  We watched for the next week and never saw another tree swallow for the remainder of the summer.  Two weeks after the tree swallows migrated away from the farm, our average number of flies increased significantly.  There was not a noticeable difference in fly count between the three pastures and the average number of flies per animal increased significantly.  On 8/12/22 we spotted horn flies for the first time that summer and fought them until the freeze in October, 2022.  

We can conclude that, when present, tree swallows were amazing at reducing the fly pressure for our cattle.  Unfortunately, because they migrate earlier than our fly season ends, additional methods need to be put in place to prevent the fly population from exploding after the birds leave.  

Tree swallows are known to be territorial and return to the same place they nested the previous year.  We are hoping that each year we will continue to have returning birds each spring.  

Project Outcomes

3 Farmers changed or adopted a practice
1 Grant received that built upon this project
1 New working collaboration
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.