Thursday, May 02, 2013

New birds and April temperatures

Nice patch of rue anemone

The first wood thrush has arrived, a dim and distant trill somewhere behind my cabin. I knew it was time. The ovenbirds arrived two days ago, and wood thrush are always close on their heels. The ovenbirds are always first, often by just a single day but never more than three days ahead of the thrush. This year the birds are actually later than is typical. My most common arrival dates for them range between April 23-27, so May 1 is a couple of days behind schedule at Roundtop. I’ve been listening for them, too, so the later date isn’t because I wasn’t paying attention.

I also heard the first blue-headed vireo last night. I never did see it. It’s a good thing the bird was nearby, even though still invisible. I have a difficult time differentiating the red-eyed vireo from the blue-headed vireo by their songs as they sound very similar to me. If the bird hadn’t been nearly overhead I’m sure I wouldn’t have identified it as anything more specific than a vireo species. As it was, I was glad the bird sang happily for a few minutes so I could be sure.

Wild turkeys continue to gobble and fly and run and scatter all over the mountain. At the moment they are more common than deer, many of which are hidden away and birthing the first fawns. The turkeys on the other hand are seriously courting, and the toms don’t care who knows it.

On an entirely different topic, last evening I was examining the average April temperatures from Harrisburg since 1935 and found something interesting. In the 1930’s and ‘40’s April’s average temperature varied much more than it has over the past 20 years or so. Earlier in the 20th century, the average temperature often varied by more than 10 degrees from one year to the next. For example the average in 1942 was 55 (high even today) but in 1943 it was just 45. Year to year variability back then was quite often 10 degrees, sometimes more. Over the past 20 years or so, that variability has much diminished and the monthly averages now rarely vary by more than 6 degrees. The temperature average itself is trending higher—certainly those low April averages in the mid-40’s seem to be a thing of the past—but the range is noticeably less.

April 2013 was higher than the average of all Harrisburg April records by nearly a full degree, but only slightly higher than the average from 1981-2010, which are the only years that meteorologists use to calculate what they consider the normal temperature they are always talking about. 2013’s higher result was almost entirely due to 3-4 days early in the month that zoomed near and into the 80’s. If not for those days the monthly average would have been slightly before average, but those days were so extreme they skewed the entire month.


Scott said...

I've never seen (or heard) a blue-headed vireo (of which I was aware), Carolyn. Maybe if I went out with the more experienced birders here in my preserve this month w would hear/see one, and they could help me to distinguish between the red-eyed and blue-headed.

It also bothers me that the "generic" meteorologists only use the last 30 years to calculate the temperature averages they report. I'm not telling you anything when I say that the long-term upward trend is very disturbing and ought to be taken into consideration.

Carolyn H said...

Scott: If you see a blue-headed vireo, it's an easy ID. But those vireos are tough to see. They blend in so much and don't move around like warblers (which makes them difficult to see, too, but in a different way).

I thoroughly don't understand how or why only the last 30 years of temperature data is all that's considered for "normal." No wonder people don't know much or even believe in about climate change. If that's all you're looking at, much of the long-term impact of the difference is already gone.