Dates are important. Always have been; just ask Julius Caesar about the Ides of March. Whether to recognize birthdays or anniversaries, or to memorialize an event for a specific reason (eg. June 6, 1944, D-Day), people all over the world have long looked at certain spots on the calendar as being significant.
Sometimes these days evoke sadness, as in the anniversary of a loved one's death; sometimes joy, like on the birthday of a relative or friend; other times it might signify nothing more than the time of year to set out tomato plants. It should come as little surprise to learn birders revere such a date too, a date on which the occurrence of rare bird sightings in the state appears to surge. Only there seems to be some dissent as to exactly when that date is.
Nearly a year ago a friend was mentioning the significance of May 23rd and all the rare bird records which seemed to be found in North Dakota on this particular day through the years. He rattled off an impressive list to back up his claim: Kentucky warbler in Grand Forks County, 2011; Lazuli bunting, Cass County, 2002; Louisiana waterthrush and worm-eating warbler, Ransom County, 2007; MacGillivray's warbler in Menoken, 1960; prothonotary warbler, Grand Forks, 1987...and the list went on. Maybe he was onto something. Maybe the birds really are calendar readers. Maybe we could make some money betting on the day of rare bird sightings.
Last weekend I happened to be out with one of the state's top birders from the Minot area, Ron Martin. After viewing a yellow-throated warbler (there are less than 10 records for North Dakota) just south of Fargo which had been discovered earlier in the day, Martin turned to me and said, "There's that May 20th thing again, everything happens on this day." Wait a minute, I thought it was the 23rd?
Corey Ellingson, another of the state's ace bird watchers, hails from Bismarck. I seemed to remember him telling me of an important May date as well so I called him Monday. "I'd say it's the 21st of May," said Ellingson, although he hedged his bet a little by adding, "There's something magical about the 20th through the 23rd of May, and I don't know what it is."
The disparity of opinion regarding this wondrous May day is telling. Certainly something is happening, why else would there be such a tight grouping to this sample size?
This year the trend has continued. Last Friday (18th) a flock of over 20 whimbrels, a rather large shorebird which nests on the tundra but is rare in North Dakota, was found in Sargent County. On Saturday (19th) a garganey (an Old World duck) was seen in Kidder County, less than five records exist for North Dakota. Sunday (20th) was the rare songbird--yellow-throated warbler--discovered just south of Fargo.
There are a couple things playing out regarding this matter in my opinion. First, the migratory birds--at least the songbirds--are at the top of the bell curve right around this time. That's backed up by another statement from Ellingson, who said, "The diversity of warblers (small, colorful, neotropic songbirds) seems to peak around this date."
Secondly, I know of some pretty accomplished birders who rarely get out much otherwise but make a big effort during this time of year. In other words, there are quite a few more practiced eyes out there seeking those rare birds.
The bottom line is this: At this particular latitude in North America there is an apparent peak of songbird migration which hasn't gone unnoticed by the local birders. With a mass of birds such as this it is not odd to locate a rarity or two in the crowd. It should nearly be expected. A particular May day might not be the definitive answer but certainly a range of days is, something like 18-25 May, give or take a few days.
Here's another tidbit to consider: Last year a small team out of Grand Forks set a record for the highest number of species seen on one calendar day in North Dakota with 168. The date? May 24th. For the chance at spotting a rarity or for just the sheer diversity of species, you might want to call in sick tomorrow. And next year plan on taking the 18th through the 25th of May off. Rest assured someone will find something rare. It might be you.