Wednesday, March 21, 2012

More on Egg #3 and will there be a fourth egg?

Tuesday was the day that our regular-as-clockwork formel was due to lay her third egg.  As the morning fog lifted over the city, she was sitting comfortably on her two eggs.

Every so often she stood up and stretched, allowing the camera viewers to do a quick count, but only two eggs each time.

At around 10:00 AM there was a changing of the guard and the tiercel settled in on the eggs.

He does not have the staying power of the formel, and soon got restless and started to preen.

He stood up, climbed to the front of the nest and appeared to be looking for his mate.

She was nowhere in sight, so he stepped back into the nest bowl and rolled the eggs

Finally the formel returned, settled back onto the eggs...

... and now seemed ready to lay that third egg.

Right around 11:30 AM, she appeared to rise up a little, looked tense and uncomfortable, and over the course of the next few minutes looked as if she might be laying her egg.

At this point, the camera watchers were in a frenzy waiting for her to move to the side a little to see if there were indeed a third egg.  But she sat right back down, and there followed a most frustrating hour when she would stand, stretch and move, but never enough to allow a clear confirmation of the third egg.

We needed dad to fly back in with food or an offer to spell her on the eggs, and finally he did.  She stood up and slowly moved, and tantalizingly the eggs came into view... one... two ...

... and then the glorious moment...THREE!

Mom wasted no time and was outta there after her arduous morning, leaving dad to inspect the latest addition to his family...

... and then get them covered up.

The formel eventually returned, ready to resume her nesting responsibilities, but the tiercel was not about to give up his spot.

He stolidly sat there as if he did not notice her looming over him!

Finally, he got up and we saw those gorgeous eggs again.

He took off, and left her gazing down at the eggs, perhaps with her three years' previous experience realizing that she was now about to settle in for the long haul of incubation.

She moved down to cover them up...

... and this final view of her early this afternoon is almost a mirror image of where she was first thing this morning, but now with three eggs safely underneath her.

There has been much speculation from Franklin Institute hawk fans about whether there could be a fourth egg, given this pair's experience and the incredibly mild winter.

Here's John Blakeman's take on that question:

The possibility of a fourth egg, at either The Franklin Institute or the New York University nests, would have been entirely dismissed by me, until last year. An experienced formel nesting at Fordham University in New York, incongruously laid, hatched, and fledged four progeny last spring. I was astonished.
Here are the cogent factors.
Much of the literature on red-tails states, with authentication, that this species can produce between one and five eggs and fledglings. Those of us who study red-tails in the Midwest and East always swallow hard when reading this datum. None of us has ever seen more than three eggs or eyasses in the wild nests we study, and we understand exactly why.
Egg production, along with successful eyass fledging, depends critically upon ample food - abundant prey animals to kill and eat. The records of four and five eggs and eyasses are primarily from the West, where the prey situation is very different from the East, South, and Midwest. In the Rockies and more western areas of the continent, there are a number of ground squirrel species that are extremely abundant in the first half of the year. These are easily captured by red-tails, allowing for maximum egg and eyass production.
Here, in the East and Midwest, the red-tails have no ground squirrels to sustain high reproductive rates. Our rural hawks mostly depend on the gerbil-sized meadow vole, Microtus pennsylvanicus. There are ample, but not abundant numbers of these. Consequently, our wild red-tails most commonly produce just one or two eyasses; occasionally three, in prime meadow habitat areas in years when the vole populations are at a cyclical high (about every 4 to 7 years).
But an Eastern nest with four eyasses? Not possible when parents depend upon voles as the prime prey species.
But in New York and Philadelphia, the red-tails that have learned to nest in cities that no longer depend upon voles. Manhattan simply doesn't have any, and only a very few  (if any) are available to the Franklin Institute hawks in the more open, grassy meadow areas within a mile of that nest.
Instead, these urban red-tails have learned to exploit new prey species, primarily the urban rat and pigeon. Yes, a moderate number of tree squirrels are taken, but the prime prey species are rats and pigeons, with rats predominating.
And that's what happened at Fordham last spring. The haggards simply loaded up on abundant rats in the area and the formel was able to produce a whopping four eggs. Subsequently, and equally remarkable, the parents were able to find and kill enough rats to keep all four eyasses in good growing health, allowing them to fledge - a remarkable achievement, afforded only because of the abundance of rats in the area.
So, yes, four eggs and eyasses are possible, but only under the most ideal conditions. First, the parents must be accomplished, experienced hawks. They can't be making any hunting mistakes while learning to provide the requisite resources for four eggs or eyasses. Secondly, the required resources - the rats in this case - simply must be open, visible, and captured. Clearly, all of this aligned at Fordham last year. But all and all, that was an anomaly. I wouldn't expect it to recur.
And I would hope that it wouldn't. Although four eyasses fledged at Fordham and could be seen parked around the area in early summer, their fates, although successfully fledged, were diminished by competition for food, especially in the last half of the summer. Lots of eyasses are not always best. All four may have starved in late summer.
Such is the fate of Western red-tails, where abundant ground squirrels produce giant broods. All is well for them until mid summer, when the vegetation in those arid regions goes dry and dormant. The ground squirrels then go into estivation  or summer hibernation. They crawl into burrows, curl up, go to sleep, and wait for cooler, moister conditions in autumn.
But this leaves large populations of young red-tails without ample prey to capture. The vast majority of the young hawks simply starve to death in the last half of summer. A few learn to hunt and kill voles (as in the East), and eke out a meager existence. After a year of this, those become accomplished hunters who can survive the seasonal loss of easy prey. But the vast majority of young red-tails simply starve. Life is tough for them, once off the nest.
So let's not wish for four eggs or eyasses at the Franklin Institute or at New York University. Two or three will be fine.
It's a spectacle in any regard, and we are so blessed to observe the hawks at both of these fine institutions.
And now that we know a bit more about their biology, their stories are even more intriguing.
--John Blakeman


  1. I bet the formel would say "Three is quite enough, thank you very much."

  2. Reading John Blakeman's post about the effects of egg-laying on the formel made me think that a fourth egg would take too much out of her. So I hoped she would not lay another. Today's entry gave me another reason to hope that she will not lay another. Three is great, I agree.