Saturday, March 08, 2008

Blakeman says: not quite yet

Pale Male and Lola on nest in early February, 2008
Photo by Bruce Yolton Http://

John Blakeman read yesterday's blog and sent in some fascinating comments:


I seriously doubt that incubation will have started when either of the birds spend the night in the nest. Some observers seem to think the night-in-the-nest behavior indicates that an egg has been laid. I'm not so sure.

I think the formel (the female -- I like that term) begins to spend the night in the nest when she perceives that she's truly gravid, that the first egg is forming and beginning to descend the fallopian tube. It can take several days for complete egg formation. In fact, the formel's behavior may begin to change from elevated hormone levels long before an egg even begins to form.

We know from watching the birds in captive breeding programs that the formel's behavior changes markedly a few days or more before the first egg is laid. She gets a bit sluggish and seems to be in a bit of discomfort. She just tends to stand with a more vacant look on her face. Instead of diligently searching for prey and flying around with the tiercel, she just perches. Physiologically, her system is changing significantly, with notable stresses. Significant quantities of calcium compounds are being extracted from her bones, along with proteins for the embryo and the egg white. Lipids are being drawn from her body and being concentrated in the developing yolk.

Consequently, she has every good reason to rest in the bowl of the nest during the night. She can stay a bit warmer there, insulated by the now-thick nest lining. She can also shape her habits into egg-sitting, not something that she would ever do at any other time of year.

Your dates are very, very interesting. I notice that the first night-sitting dates are near the end of the first week in March, with most of the hatching dates in mid-April. If the first dates are real sitting, incubation-start dates, they put the incubation period in the realm of five weeks. In reality, it's closer to a bit over four weeks. I think this first week of sitting behavior actually happens before a real egg is laid.

I'm sure other observers have seen the following noteworthy behavior at 927. Until the last egg is laid, until incubation begins in earnest, the formel tends to sit just a bit higher in the nest. At times, she will hunker down deeply in the nest, but at most early times she will sit a bit higher at the start. But when the final egg has been laid, she will lay down very low in the nest at all times.
Incubation almost surely would not begin just now, unless Lola is to lay only a single egg this year. That's not likely. She's healthy. There's plenty of food. She will most likely lay two or three eggs this year, as before.

This time, she will not have to contend with the eggs wedged between the pigeon spikes. She will be able to instinctively roll them and keep them warm.

The reproductive season has begun -- with so much better hope than the last three.

--John Blakeman

Friday, March 07, 2008

Lola's first night on nest

Pale Male and Lola on the nest -- March 6, 2008
Courtesy of [click on photo to enlarge]

The date on which Lola first spends the night on the nest, which is also the time she and Pale Male begin to exchange sitting duty so the nest is attended at all times, is a landmark for Hawkwatchers. It may not mean that actual incubation has begun -- there are probably a few practice days that go by before egg laying begins and incubation begins in earnest. But we keep track of that date. It means that real incubation is imminent--will begin within a few days.

Yesterday, March 6, was the day!

Here are some "first night on nest" dates for past years

2007 -- 3/10
2006 -- 3/5
2005 -- 3/8
2004 -- 3/7
2003 -- 3/7
2002 -- 3/7
2001 -- 3/10
2000 -- 3/8

The eggs last hatched in 2004. Here are some hatch dates:
2004 -- 4/15
2003 -- 4/16
2002 -- 4/11
2001 -- 4/18
2000 -- 4/16

Because we can't see into the nest, we get these figures by observing changes in behavior. We assume a hatch has occurred when we see something like feeding fehavior happening: the female stands on the nest's rim and makes up and down movements to the nest's bottom.
It's not exactly rocket science. But still you can see the amazing regularity of the hawks' schedules.

Hurray, the process continues! And this year with a bit more hope.

Wednesday, March 05, 2008

Spring is coming- and so is Starr

Many readers are writing in to inquire about possible bird walks in Central Park during the migration seasons. Starr Saphir has been leading walks for many years, and I always post her schedule when spring is approaching. Well, it's approaching! Here is Starr's schedule:

Starr Saphir's Spring Birdwalks in Central Park

Mon., Tues., Wed., and Sat. mornings from Tues., April 1 through Sat., May 31

Mon. and Wed. mornings from Wed., April 2 through Wed., May 28.
Where: 81st St. and Central Park West, the SE corner
When: 7:30 AM (sharp) until we run out of birds (usually 3-5 hrs.; people leave when they wish)

Tues. mornings, from Tues, April 1 through May 27.
Where: 103rd St. and Central Park West, the Park side
When: 9:00 AM (sharp) until we run out of birds

Sat. mornings, April 5 through May 31
Where: 103rd St. and Central Park West, the Park side
When: 7:30 AM (sharp), ending as above

For further information please call Starr Saphir at (917) 306-3808. No registration necessary, just show up. All walks non-smoking.

Fee: $6 for adults, $3 for full-time students. See you in the Park!

Tuesday, March 04, 2008

Riverside Redtails: Lookin' good

John Blakeman writes:

The posting [yesterday-3/3/08] on of the Riverside Park nest was gratifying. It has reached a much larger size, closer to Red-tail nests that are typically successful.

From the hawk standing on the nest, I extrapolated its size to the nest itself. The nest is presently about 24 inches across the top, which is very adequate. It's about 14 inches deep, which is still a bit shallow. But it's still only the first days in March and more sticks will be brought to the nest in the next two or three weeks, before eggs are laid.

I'm very encouraged by this photo. The pair looks like it's diligently attempting to nest, not just going through the motions as do so many young, first-time Red-tail nesters.

Lookin' good.

--John Blakeman

Monday, March 03, 2008

Bob Levy : the musical countdown [cont.]

photo by Bob Levy 2/22/08
Bob writes: On Friday February 22, arguably the most wintry of days so far this season, as six inches of snow covered Central Park and more was falling I heard a male Northern Cardinal sing. That was the first cardinal song I detected this year and I took it as a musical sign that Spring is near. Since then I have heard other males sing and just yesterday I saw the surest sign that Spring is closing in: I watched a male Northern Cardinal feed his mate. Nest building can’t be far away now. Keep your ears open. More songs are on the way.

Sunday, March 02, 2008


Photo by Cal Vornberger - Turtle Pond 7/1/05
[http://www.calvorn. com]

Every year I wait for it, and yesterday I found it. It appeared on Jack Meyer's e-birds report of birds seen and heard that morning on his daily walk in Central Park:

1 March 2008
Red-winged Blackbird (Several, at least two singing).

Once the other migrants start arriving we stop hearing the red-winged blackbird song--it becomes too common and fades into the background. But now it thrills the ear. The spring countdown has begun.