Cooper's Hawks Update 3: Winnowing

To see earlier posts on the Cooper’s hawk project, see these links:

This third update recounts events starting on June 18, 2016.

June 18:

The larger of the young are just at that tween stage, where they are about to look more like hawks than hatchlings. It happens, very, very rapidly, and is all the more stark when you have a clutch such as this, with three very different size/maturity stages.

This picture is of one of the two largest chicks attempting to call through the forest to the mother after a feeding. Note the full crop.

The feedings in the past few days have generally taken place out of sight, behind the main tree trunk, so I have few useful observations about the ongoing drama of whether or not the fifth and sixth chick are getting enough food – and by what mechanism. I can say that the smallest one does not look like it has been growing at nearly the rate the others have, and that it is inordinately sleepy.

Soon, the mother will want to leave food for the larger chicks to pull apart, and it will be an interesting issue for the younger chicks, who don’t have that capability.

It has been several days since I’ve seen all six young in the same picture, which makes me think that there’s a possibility one didn’t make it (I thought this incorrectly several times last year). I suspect that the sixth chick we saw in just one image may not have made it through the day it hatched. The second to last hatchling looks like it is continuing to go downhill.

The parents appear to have been hunting the mixed stand northwest of the nest, which extends up Hubbard Hill and has perhaps 20 acres of mostly hemlocks. I surmise this from the location from which I hear calling, as well as the direction of flight to and from the nest. It is rife with red squirrels, and has a few hundred feet of old stone wall that is likely better than most areas to find chipmunks. [Update from July: around this time, Forest Metrix co-founder Donn Downey, who lives about two miles in that direction reported seeing a Cooper’s hawk returning from his woodlot in the direction of this nest. It is possible that this is one of the parents, although that would be a slightly lengthy commute for most Cooper’s hawks between nest and hunting grounds. The literature shows that this is more often one half to a full mile.]

June 21:

Feeding of the chicks has not been consistent from day-to-day, with one day showing a feeding every 40 minutes for a long period of time, and the last couple of days showing feedings every few hours. I’m not sure if this is a product of the size of the prey brought, or – as I suspect – the varying difficulty of finding any prey at all.

As the smallest failed, the others found it very curious

The littlest one (of 5 apparently remaining) looks like he’s on a downward trend, and I think he will very possibly starve. I also suspect he has a tick on the back of his neck, which is interesting in that a researcher from West Virginia asked me to look out specifically for them on the hawks. She was thinking more about them lodging on the periorbital area. It is also interesting because I wonder if that sort of explains some of the “pecking” I was seeing. It may be that the siblings were eating ticks off the little ones, which would be a much more generous interpretation of their actions. The less generous one is that I’m not seeing a tick, but rather a wound created by a sibling. Having seen a chick scratch his own neck with a talon, it could also be that a chick could wound itself while trying to remove a tick.

I can say – to my surprise – that there are ticks on the trees up at 75 feet. Previously, I’d assumed any tick seen on a bird would have been from prey. My tick tree inventory for the 2016 season: I’ve seen two ticks on branches, both very close to the trunk of the big tooth aspen used to climb next to the nest subject tree.

The littlest bird was drooping his head over the edge of the nest so frequently, that the other chicks stood around him at times and just stared, as in the picture above. I wondered if they were wondering if he was going to become food. I have not seen his crop full at any recent feeding.

I am getting more and more evidence that the adult female is deliberately gaming the feeding order by giving large, awkward pieces to the biggest young (legs with claws, furry tails, etc) and then getting choice meat parts and handing them to the smallest bird, giving him about a one-in-three chance of keeping it. I have three different photo series of this behavior – enough so that I think it’s less and less likely to be coincidental.

Incidentally, today (2 weeks after the first hatch), the largest bird did his first hop. Preceded by a bit of experimental flapping. Last year, there was more of a flapping hobby for a few days before everyone got hoppy.

Grooming or coercion? These beak holds happened throughout the nesting period, and sometimes caused visible, bleeding scratches.

Branching should be happening not long after (the young hang out on nearby branches). This will force me to use a wider lens to capture all the limb activity, and will result in poorer close-ups of the growing hawks.

As seen at left, one bird would sometimes be seen to exert what seemed like a dominance display over another bird, holding the other bird’s beak in its mouth. Because our data is in the form of still pictures, it is difficult to know how gentle or violent it was, but we can say that it sometimes resulted in bleeding wounds. The bird that appeared to be subdominant would not make much attempt to escape and would generally stay very still.

Perhaps the funniest series caught in the entire nesting series was the time that the largest bird decided she’d grown up and wanted to sleep standing up, like the adult female. That series is reproduced below, starting with the young bird proudly roosting, looking out from the nest as would an adult… and then very slowly collapsing over a period of a few minutes.