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Tracking Blackbirds With Radar

Monday, February 1, 2021
filed under: Birds

        Weather radar isn’t just for forecasting the weather.  Researchers also have figured out how to use Next Generation Weather Radar (NEXRAD) to track blackbirds — and that could lead to better yields and more profit for sunflower producers.
        Using Weather Surveillance Radar (WSR) data from 2012 to 2019, University of Oklahoma graduate student Bonne Clark, in collaboration with the USDA Wildlife Services-National Wildlife Research Center and the University of Notre Dame, monitored one large roost near the McKenzie Slough, just east of Bismarck, N.D.  This study comprised the first time weather radar had been used for evaluating uses of radar for monitoring agricultural damage from birds. 
radar showing blackbirds leaving roost

        Clark notes that the main objective of the study was to present a method for estimating sunflower damage using radar-derived bird abundances.  Her team used radar as a method to count blackbirds at this roost, coupled with economic damage estimates.  They hoped to collect new information about when damage to sunflower from blackbirds is the most severe, which in turn is reliant on when the birds arrive, when the roost population reaches peak numbers, and when they depart.
        She found that at the mega-roost in the McKenzie Slough, blackbird numbers routinely peaked in mid- to late October — around the same time that the peak of mature sunflower remained unharvested. 
        North Dakota producers lose an estimated $3.5 million to blackbirds every year.  Bird damage to sunflower takes place over an eight-week period from mid-August until mid-October.  Crop damage is the greatest within approximately 10 km — about six miles — of roosts, where damage often exceeds 20% yield loss.
Bonne Clark
Bonne Clark

       Clark was able to identify biological scatter detected by WSR as blackbirds. While meteorologists scrub out the biological data from radar to forecast the weather, she did the opposite — scrubbing out the weather data to focus on biological data.
     “Radar is used primarily for forecasting weather, but it is a great tool that is free to use,” Clark explains. “There is archived data available for the past 25 years.”
        Clark’s research also included ground observations at the McKenzie Slough.  In 2019, teams of two observed the blackbirds from mid-September to late October.  They estimated the number of birds per minute as they departed the roost in flight lines or flocks.  Observations began near sunrise, when the first flock emerged.                                                                                          
        Their observations added up to a lot of birds: the number of maximum blackbirds estimated with radar, per day, ranged from nearly 347,000 to more than a million.  Those maximum counts typically occurred in mid- to late October, or occasionally the first week of November — and one year in early August.  In 2016, they recorded an estimated 1,076,140 blackbirds on a single day in late October.
        All those blackbirds can cause significant damage to sunflower fields.  Clark’s estimates of damage to sunflower from blackbirds during 2012-2019 was greatest in 2015, when potential losses were more than $41,000 for sunflower fields near the roost due to the early arrival of blackbirds that stayed throughout the fall.  Other years had damages totaling anywhere from $12,000 to nearly $21,000.
        “Blackbird numbers routinely reached large numbers when the mature, yet unharvested, sunflower remained. ?We determined that if producers could harvest their sunflower two weeks earlier, they could save as much as $1,800 year around this single roost,”?Clark states.  “This means that if you have several fields around large blackbird roosts, you may evade even more damages.  Those two weeks could make a big difference in bird damage.
        Planting early, choosing early maturing varieties and desiccating the crop could lead to an earlier harvest and put more money in producers’ pockets.”
        Clark emphasizes that a coordinated harvest effort among neighbors would be vital to an earlier harvest approach.  If one neighbor harvests early but others don’t, the birds will still find the isolated sunflower fields, and those producers may suffer severe bird damage.
        Clark stresses this isn’t a cure-all for blackbird issues.  She says it’s still important to use a combined approach with other management tools.
        She reiterates that radar can be used to help predict bird movement, much the same way that meteorologists use radar to predict weather events.  Knowing when the birds will be arriving can help producers plan their planting and harvesting dates to avoid large flocks of blackbirds, and to implement management tools prior to the arrival of large blackbird flocks.
        Clark says this project is only the beginning.  “It has definitely sparked some more ideas,” she says. “I am interested in looking at how weather and landscape factors correlate with trends in blackbirds and migration timing.”
        There currently only three NEXRAD radars in North Dakota, located in Bismarck, Minot and Grand Forks.  But Clark says other radars have the potential to monitor known blackbird roosts. 
          Along with sunflower, she says the methods in her research could be expanded to other crops also damaged by blackbirds, such as corn and rice. — Jody Kerzman
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