When using bird deterrents in sweet cherries makes sense
In early varieties, small blocks and in years when sweet cherry yields are expected to be low, losses by birds are expected to be higher and protecting fruit from birds may make good economic sense.
Whether and how much to invest in bird management in a given year will depend on the costs of bird management versus anticipated fruit losses. Michigan tree fruit growers are not likely to forget the 2012 season when weather conditions caused extensive fruit losses and very low yields. These very low yields in 2012 followed by two seasons of normal to high yields in 2013 and 2014 provided an unexpected opportunity to learn about how fruit losses to birds change with the amount of fruit present in a given orchard.
Our research group conducted bird damage assessments in sweet cherry orchards in northwestern Michigan in all three years. We counted the number of cherries per 1 meter of branch length from 60 trees per block at six sites each year. Cherries along each branch were categorized as intact, bird-damaged or missing (fresh pedicel present, but fruit missing). We were careful to distinguish bird damage from mammal damage. Because we sampled the same number of branches each year, the total number of fruit sampled provides an index of fruit abundance for each block each year.
We found that the highest percent bird losses occurred in 2012, when fruit abundance was very low. Conversely, when fruit abundance was much higher in 2013 and 2014, percent fruit loss to birds was much lower (see figures).
These findings along with some of our previous work suggest there are two main principles to successful bird management:
- When there is less fruit in a given area, there will be a higher percent loss compared to areas with more fruit. Thus, expect a higher proportion of damage in low-yield years, early-ripening varieties (birds will have few alternatives) and small blocks.
- Blocks near resources important to birds are at higher risk for damage. For example, bird damage is expected to be higher in blocks under wires, at the edges of blocks, near night roosting sites and in isolated blocks with little human activity.
It is also important to note our results suggest bird deterrent techniques like various types of scare devices may have little impact in large blocks when yields are high, as they were in 2013 and 2014.
When planning a bird management strategy, consider the following:
- Each year and farm is unique and should be assessed for potential risk factors (see “Sample Bird Management Plan”, pages 211-218).
- Using multiple types of deterrents, deploying them early in the growing season and moving them frequently should enhance their effectiveness in deterring birds.
Thanks to the Specialty Crop Research Initiative of the U.S.D.A., the Cherry Marketing Institute, the Michigan Grape and Wine Industry Council and the Michigan Apple Committee for funding and support. We are very grateful to the many Michigan fruit growers who have spent their time with us and provided access to their fields.