In 9 of 16 Seasons, Illinois River Mallards Peaked Within a Week of Thanksgiving

IPicking Days

Every Season's Mallard Peak Came Between Nov 8 and Dec 12

The peak fell after Thanksgiving in 10 seasons and before it in 6, and across all 16 seasons the median came 5 days after. Ten seasons had their peak in November and six in December. In 2025-26 the peak landed on Nov 28, one day after Thanksgiving.

Each fall INHS flies the river about once a week and lists a mallard count for every survey site. The counts are in its aerial inventory reports such as the August 31, 2023 flight report and the December 2009 flight report posted by the Illinois Department of Natural Resources. We have 237 survey flights in our files from late August through January in the 2009-10 to 2025-26 seasons, with 2017-18 missing. Adding the site counts matches the printed river total on 235 of the 236 flights we could check.

Seasonal peak counts swung widely. Peaks in the series ranged from 96,690 mallards in 2010-11 to 488,570 in 2012-13. The 2012-13 peak also shared the latest date of Dec 12 with 2016-17. The earliest peak fell on Nov 8 in 2013-14 at 329,590 mallards.

IICloser Lately

Seven of the Last Eight Peaks Came Within a Week of Thanksgiving

Peaks in recent seasons have stayed nearer the holiday. Only 2 peaks fell within a week of Thanksgiving in the first eight seasons in our files (2009-10 through 2016-17). Those eight peaks ranged from 20 days before the holiday to 20 days after. In the last eight (2018-19 through 2025-26) the count was 7 of 8. The range was 8 days before to 6 days after, with 2018-19 the one miss at 8 days before.

Eight seasons on either side makes a small sample, and the flights are about a week apart. These counts cannot explain why peaks have bunched near the holiday.

IIIStaying High

Counts Were Highest From Mid-November Through Mid-December

A single survey at the peak leaves a narrow target. For planning use the half-peak window from the season's first survey with at least half its peak count to its last such survey, though counts can dip between. In the 16 seasons the median first survey at or above half the season's peak count was around Nov 12, and the median last survey at that level was around Dec 22.

Averaging the seasons with a survey in each half-month puts surveys in the first half of October at only 6% of the eventual peak. Counts reached 21% of the eventual peak in the second half of October and 56% in early November. Counts in the second half of November reached 79%, the best half-month of the season. Counts in the first half of December stayed almost as high at 75%. Counts then dropped fast to 52% in late December and 31% in the first half of January.

Any one season can have a tighter or looser window. The half-peak window in 2012-13 covered only Dec 6 to Dec 19, and in 2013-14 it ran from Nov 8 to Nov 27. The window in 2019-20 stretched from Oct 28 to Jan 2.

IVHolding Spots

Five Site Rows Held About Half of the Counted Mallards

INHS repeats two site names in its tables. The Upper block has Goose Lake twice and the Lower block has Big Lake twice, so we kept the rows separate in the order INHS prints them. In the Upper block the second Goose Lake row appears between Douglas Lake and Upper Peoria. That row held 15.6% of all mallards counted over the 16 seasons, the largest share of any site. The next shares were Chautauqua at 9.9%, Douglas Lake at 9.3%, Duck Creek at 8.1%, and the single Emiquon and Spoon Bottoms row at 6.4%. Together those five rows held 49.3% of mallards counted on the survey.

With two of the top five rows in the Upper block and three in the Lower block, neither end of the river holds a lock on the birds. The blocks did not follow a north-to-south order in their peaks either. In only 3 seasons did the Upper block peak first, while the Upper and Lower blocks peaked on the same survey flight in 5 seasons. The Upper block peaked a median of 4 days after the Lower block.

VSurvey Timing

A Peak Date Is Accurate to About a Week

These aerial counts of mallards on survey sites do not record harvest and miss birds elsewhere in the valley. With flights about a week apart, the true peak could come a few days before or after the peak survey. Some top sites are refuges or closed water, so not all birds counted there are huntable. The half-peak window reached the last flight in 2016-17, 2023-24 and 2024-25 so birds in those seasons may have stayed longer than the table shows. Flights stopped in late December in two seasons, which would have left a January peak uncounted. We left 124 rows out of the site shares because INHS printed them for a combined Illinois River Valley block in 2021-22. The counts tell us when mallards were on the river without explaining why one season peaked early and another late. Our field guide on cold and snow looks at the weather side, where mallards on Missouri public ground stayed until cold and snow stacked up.

VIChoosing Your Week

Begin Your Week on Thanksgiving Day and Leave Early December Open

Our rule for an Illinois River hunter taking one week is to begin on Thanksgiving Day. The week includes the median peak 5 days after the holiday, and it covered the peak survey in 6 of the 16 seasons and 5 of the last 8. If you can divide your days, use a few in mid-November and hold the rest for the first two weeks of December. Look at the latest INHS flight before using scarce days in October or January.