Field notes: August

Not one or two missing. All twelve, gone at the same time, in every one of the thirteen species examined at Powdermill, a bird banding station in western Pennsylvania. Mumme, Mulvihill and Norman went through fifteen seasons of records there, 1,289 captures, and published what was in them in 2021. A warbler at the peak of its annual molt is replacing between half and two thirds of its forty-eight flight feathers at once. The tail is bare. Six to ten of the long feathers on each wing are missing or half-grown. The bird holds that condition for two to three weeks, sometimes longer.

It does this in the weeks before it migrates.

The paper is careful and so should we be. A molting warbler is not grounded, it is compromised. The authors write that flight in this state is "likely to present numerous challenges." But it answers a question a lot of people have in August without quite asking it, which is where the birds went. The woods are not empty. They are full of birds with very good reasons not to draw attention to themselves, staying low in the cover until the feathers come back.

The part that surprised the researchers was the timing. You would expect the species that start late to hurry, having less of the season left. They do the opposite. Late molters grow their feathers more slowly than early molters, and the explanation the authors give is this: a feather is built out of food, food has to be found in daylight, and by late summer there is less daylight to find it in. The day length is setting the pace at which the feather can grow.

And the day length is moving faster than it was.

An hour and five minutes has gone since the June solstice at forty degrees north. Almost nobody noticed it go, because through early July it left at about a minute a day. Today it is leaving at two minutes and fifteen seconds a day, and that rate keeps climbing until the equinox.

Which makes the arithmetic run the opposite way from how the season feels. More daylight will disappear in the forty-four days between today and late September than disappeared in the fifty days since the solstice. Sixty-five minutes went slowly. A hundred and ten more are going faster, in less time.

The end it goes from has changed too. Through early July the shortening was almost entirely in the morning: the sun rose later and set at nearly the same hour. Over the next ten days the sun will rise about ten minutes later and set about thirteen minutes earlier. The evening is the end that is closing now. That is probably why late August feels like a different season from early August, when the calendar says almost nothing has happened.

Lower down, in the tall weeds at the edge of any field or parking lot, the spiders have reached full size.

The black and yellow garden spider, Argiope aurantia, is the one whose web you walk into in August. The females are large by now and hard to miss, and their webs carry a heavy zigzag of white silk down the middle. You have probably been told what it is for. The usual explanation is that it reflects ultraviolet light and draws insects in.

In 1999 Blackledge and Wenzel tested that on this species directly, and got the opposite. Webs with the zigzag caught almost thirty percent less prey than webs without it. The band is not a lure. Their reading, and the one their data supported, is that it is a warning sign, a marker visible enough that birds do not fly through the web and wreck several hours of work.

So she pays close to a third of her catch to advertise the web to the animals she does not want, in order to keep it intact for the ones she does.

That was twenty-seven years ago and the question is still open. Other Argiope species do appear to draw prey with theirs. Another line of research thinks the band is about vibration rather than vision. After decades of argument about a piece of silk anyone can find in a hedge in August, it is not settled. That is not a failure of science. It is what an unfinished question looks like from the outside.

And then the water.

The ocean runs weeks behind the sky. Along most of the open mid-Atlantic coast the sea is at its warmest now, not in July. At Cape May the water averages seventy-four degrees in July, seventy-six in August, and is already falling back by September. The warmest month in the water is this one, roughly two months after the longest day, at the point in the calendar when the light is going faster than at any time since spring.

So this is the week. Birds in the cover that are compromised in the air, growing feathers at a speed the daylight is setting. Evenings closing thirteen minutes at a time. A spider paying a third of her catch for a warning flag nobody has explained. And the sea at its warmest on the way down.

The molting warbler is in whatever cover is nearest to you. The spider is in the weeds at the edge of the parking lot.

What have you noticed changing this month, before anyone told you it had?