Wednesday, June 30, 2010

Why Do Bobolinks Stop Singing In Early July?

As a kid growing up in Northern Wisconsin I remember always looking forward to the days between May 1 and May 5 when, just like clockwork, Bobolink's returned from their winter habitats on tropical and subtropical grasslands of Argentina, Bolivia, Brazil and Paraguay. Their return was exciting for me because I got to listen to their nearly-indescribable voice each time I was anywhere near a grassy field.

Bobolinks always livened up summer days whether it was as a kid in Wisconsin, or later while living in North Dakota or Nebraska. I remember quite well in the early 1980s doing breeding bird censuses on native prairie plots near Woodworth, North Dakota, that Douglas Johnson had maintained for many years. Plot number 11 was always the one where you could be assured that you would have to scratch your head for awhile trying to figure out which male was singing on whose territory and how do you map all of that on an 8 x 10 piece of paper. In Nebraska we found Bobolink's to be quite common in the eastern half of the Platte River Valley, where they especially liked wet meadows along the river, and nearby alfalfa fields for nesting.

In the summer of 1978 Hal Kantrud and I were able to listen to Bobolinks singing on native prairie research plots all over both Dakotas and Montana and even a few in Wyoming. In 1980 and 1981 I remember finding them on native grasslands and in domestic hay fields throughout west central Manitoba and east central Saskatchewan.

Still, no matter where I was looking for them when July 1 came on the calendar it seemed like some switch went off in the head of Bobolink's and they stopped singing. At least they greatly reduced their song output. Go out on a patch of prairie on the Mormon Island preserve south of Grand Island Nebraska this evening and if there are no tornadoes around, you will hear a feast of Bobolink voices. Go out to Mormon Island in 24 hours and you'll hear 1/4 the voices you heard today. Go there a week from today and you'll be telling yourself you have to wait until next year to hear them again.

In fact, the latest day on which I have ever heard a Bobolink singing anywhere was July 7, 2007 when I found one bedraggled male still singing from the grasslands adjacent to the Halifax International Airport in Nova Scotia, Canada.

Why Bobolinks abruptly cease to sing on July 1 is one of those ornithological mysteries that will always be a mystery. Mourning Warblers return to northern Wisconsin about the same time as Bobolink's return and like the Bobolink's they beginning singing the moment they alight on their territory, but Mourning Warblers keep singing, at least occasionally, through July and into early August. Northern Parula start singing here in late February and continue to do so well into mid-August. But for Bobolinks, its a two month show and then its over.

This past spring I found Bobolink in abundance on the Kissimmee Prairie Preserve State Park in Okeechobee County Florida in late April. A week later I found several migrant Bobolink in Glades County near the southwest shore of Lake Okeechobee. There were also a few along the beach at Lido Key in Sarasota, County. Luckily for me at least some of the birds in Okeechobee and Glades Counties were singing. I listened to them and wondered where they would be a week from that day.

However despite where they were going, in all likelihood the song fest that is a Bobolink is going to substantially shut down beginning tomorrow morning at sunrise on July 1.

I always knew there was a reason I didn't like July.