A Q&A with Jerome Jourdan of the Detroit River Hawk Watch
Every fall, billions of birds migrate south for the winter in a display that can be breathtaking to witness. Some do it every day.
That includes the people who run the Detroit River Hawk Watch, an annual survey of raptor and turkey vulture migration patterns as they pass over Lake Erie Metropark. For the past 38 years, at least one person has been counting hawks at the site to track the population, see variations in numbers, and feed them into a national database that analyzes trends and the health of hawk populations across North America.
Every day between Sept. 1 and Nov. 30, one paid worker and a rotating group of volunteer assistants sit at the same place in the Metropark and count how many hawks pass overhead. In some years 18 different species might migrate. In total, these citizen scientists spent 568 hours counting 72,585 hawks in 2020.
To learn more about the Detroit River Hawk Watch, what trends have been noticed over the years, and what they indicate about the state of Michigan’s environment, we spoke with Jerome Jourdan, a bird hobbyist (he also runs a website on bird photography), member of the watch’s advisory committee, and the primary author of the project’s 2020 report.
Planet Detroit: How exactly is the Hawk Watch conducted?
We have a contract counter, Kevin Georg. He’s been doing the seasonal count for four years now but has 35 years of experience from other sites across Michigan and Pennsylvania. Then we have a group of volunteers that assist him. We’re a volunteer-driven organization. The success of the program really is due to the dedication of volunteer hawk watchers, coming out here every day for three months, rain or shine, and counting for eight hours a day for nothing. They deserve a whole lot of credit.
We then post the daily results, seven days a week, for the entire 90 days in the fall on our Facebook group. I publish the results on hawkcount.org and another volunteer writes the narrative summarizing the day’s experience. We also make predictions about what we expect to see based on prevailing winds, weather, and barometric readings.
Roughly 15 to 18 species of hawks can migrate through the Detroit River. But the main ones are turkey vultures, broad-winged hawks, red-tailed hawks, and sharp-shinned hawks.
Counting hundreds of birds individually at once seems impossible. How is the counting actually done?
One of the skills of counters is the ability to estimate big numbers of birds. Turkey vultures tend to kettle, or form big swirling groups, over Canada. You’ll see a small tornado of several hundred birds rising up over the horizon, and they have a tendency to drift over the count site and then stream across in a straight line.
Counters will count in clusters. They’ll count 10 birds, measure that space, and then have an idea of how much area 100 birds is. Then they’ll add those areas up to get a total. A lot of times, the birds come over in low enough numbers that they can be identified and counted individually. But for broadwing hawks or turkey vultures, when we get big kettles of thousands of birds, they’ll cluster count.
This is also part of a scientific study, so we have specific protocols for counting birds. You can’t use a binocular greater than 10 magnification power. If you’re using a spotting scope, you can only use it to identify birds, but not count birds. Otherwise, you might be expanding the count area and technically be outside it.
What trends have been spotted over the 38 years that this project has been running?
Our numbers are compiled along with some 200 other hawk watchers across North America. Scientists and academics use the data to compile the raptor population index (RPI), which gives a screenshot of individual species populations at each of the sites They plot the trends of the seasonal counts over those time periods, which gives us a screenshot of the health of the population.
For instance, for many years in the Great Lakes region, bald eagles were practically extinct because of DDT. But the population rebounded in the 1990s after Lake Erie was cleaned up and we got rid of DDT. The RPI shows that the health of the bald eagle improved greatly over that time period. Now there are other species, like sharp-shinned hawks, whose numbers have been steadily declining over the past 10 years. There are a number of factors involved, like the weather. But much of it might be due to reduced habitat, predation by larger hawks, and lack of insects as a food source. Insect populations have been declining drastically, which means less food for birds.
What does that say about the health of the environment?
Well, over the last 10 years, only one species, the bald eagle, has shown a meaningful increase in population. Whereas 15 of the 18 species that we monitor have all shown moderate to severe declines.
We’ve been looking at causes for the population decline. Habitat destruction is certainly a big one. We’re paying more attention to insect populations. There are concerns about the number of windmill farms going up — a lot of these tend to pop up in major bird flyways and might be affecting populations.
Many factors can contribute to fluctuations like these. Interestingly, over the past 25 years, we’ve also seen somewhat cyclical trends in populations. It’s kind of like a roller coaster — for several years the numbers will be going up, peak, then go back down. But in the last 10 to 15 years or so, the rate at which these peaks and valleys are occurring is more frequent.
What interesting results are in the 2020 report?
Last year we were on trend to have a record year for the number of birds passing through the site. But one of the things that prevented that were unusually high winds in the middle of September, which pushed a lot of these birds south of the count site.
That was especially true in September for broadcasting hawks, which come through the count site all at once. In 1999 for example, on Sept. 17, the Detroit River counted 500,000 broadwing hawks in a single day — that was a North American record. It’s one of those species where over a three to four day period, you can get anywhere from 30,000 to 50,000 per day if the weather is good. But this year on the 17th, the winds were too strong at our site, which pushed the birds over Lake Erie, and we counted only 400. For that reason, September ended up being a low count month for us.
But we had a banner year for turkey vultures migrate through. We ended up with 69,727 in the month of October. That was one of the highlights of the year.