Yesterday was day 31 of the Cooper’s hawks’ first hatching. A lot has happened in the past 7 days, since the last update. As I suspected, soon after the last update, they fledged.
I was up in the tree when I believe it first happened, although it could be that this was just a reprise of an earlier flight. One launched for a tree and seemed to miss the mark and either A) plummeted fairly quickly to the ground or B) was doing one of those drop flights that the Coopers do, and evened out, buzzing the ground before alighting elsewhere. It looked like the former, unfortunately, and that night I was worried for it, until I saw all four back in the nest hungrily tearing up a bird the next morning. The other three had short, clumsy flights to the nearby white pine.
Last night I spent 20 minutes in the observation tree just enjoying the canopy, observing what I thought was an empty nest. Through this quiet enjoyment I realized there were two young in the tree just south of the observation tree. They sat probably 10 yards away from me, more concerned with rustling of squirrels down below than with their serial voyeur. I watched one of the two has it became antsy, appearing to wish to fly down and eat the noisemaker. After swapping feet a few times on the branch, it leapt off and by the angle of its head looked as though it intended to stoop down to the squirrel, but its body decides instead to drop rather alarmingly at about a 90-degree angle to that desired path. Much flapping through leaves and branches ensued, and it would up catching itself and landing on a branch of another tree about half-way to the ground. I am not sure, but I think this was a practice attempt at hunting, as miserably poor as it seemed. Cooper’s generally nest about 1/2 of the height of this Cooper’s nest (75’), and I’m not sure if that is an advantage to these fledglings. It had plenty of altitude to burn in order to catch itself, but then again, its target was a long ways down through lots of branches, and gravity by itself provides a velocity of 11 meters per second in a free fall from that height.
The four surviving birds are large, looking like real hawks, although they show to be roughly 1/2 the size of the mother when she lands among them. One is on the nest at almost all times, and I suspect it is a single individual who holds vigil for parent-borne food. It works pretty well for her, as she winds up winning the first part of the feast for perhaps a minute before the others start arriving once some prey is brought. Two siblings come about a minute apart, and the fourth one sometimes comes and sometimes does not. That fourth one is probably the best flyer, landing nimbly, without the desperate stumbling that the others show.
Here (left) is a picture from July 1 that shows the three who consistently show for feedings. The one in the back left is a female, I believe. The others appear to be male, although either could be a male from the first hatching, or a female from one of the later hatchings. It is muddled.
Here (below) is an image from a week prior to show the amazing growth spurt that happens starting after week 3. The growth in that week is startling, although some of it is deceptive. Like the shaggy dog who gets the bath, these birds “growth” is largely do to feathers coming out and obscuring their still somewhat scrawny bodies.
I note that, while the birds fledged earlier than the chicks last year, the parents are bringing food to the nest more consistently post-fledging, for a longer period of time. I wonder if it has to do with this reluctant fledger who is not following the pack of siblings to the lower altitude butchers block trees, where parents appear to start to tempt the young to do more of the work themselves. As it is now, the mother is still stripping meat in the nest for a time before leaving about half the carcass to be processed by the young.
A few researchers have expressed interest in the data collected. I’m starting to better document the methods and limitations of this data collection so as to be more usefully applied. Yesterday we passed the 220,000 photos mark, and I expect we’ll top out at around a bit over a quarter million before the birds become too mobile to keep tracking.
One of the researchers is interested in creating a growth guide to help other researchers age Cooper’s chicks. This is proving slightly problematic, as I’m finding that in this wild-grown bunch, their inconsistent nutrition means that their growth rates are wildly volatile between birds and stretches of time, and that even basic development milestones are completely deferred when the chick isn’t getting enough food. The chick at left above (the now-deceased “fifth” chick) looks about a week old, where his siblings look more than twice that. This itself is interesting, as the age progression images I’ve seen in the literature were made with hand-raised birds, which probably gives a superior average in sizes and development milestones, but may also exaggerate growth, and not reveal the amplitude of the variance. It doesn’t help that it is extremely difficult or impossible to tell birds from one another at this stage, barring some unique characteristic.
The fur bearing food supply has kept up, after a period of more birds taken to the nest. More red squirrels than birds in the past few days, with a couple chipmunks thrown in as well.
On Sunday the 3rd, the 30th day, the chicks all made adult calls for the first time. In the morning one chick did this as I climbed up the ladder. The mother was ripping up a red squirrel, not noticing, and the chick gave an alarm call that caused the mother to look and take off. Later in the afternoon as a I climbed again to swap cameras, all of the chicks gave little protest calls from their various perches, all within about 50 yards of the nest.
When the young fly, they tend to fly over toward the same area the previous year’s litter did, near a particular butchers block tree. When the adults fly, they appear to move over toward the site of last year’s nest, or perhaps the tree I instrumented to climb and photograph from in 2015. It is difficult to tell when up in the canopy, as the old nest site is about 150 yards away.
The literature gives a likelihood of a given couple of birds to renest in the same place the next year. But the way biologists have calculated this in the past isn’t by whether a bird uses the same nest, but rather whether the bird uses a nest within an arbitrary distance of the older nest; often 100 feet. Technically, this year’s nest could be a renesting by one standard, but outside by most others. Incidentally, the figure for renesting in a subsequent year is about a third of the time, using what I’d consider a generous radius for the standard.
On July 3, I witnessed some interesting behavior between two of the young. They appeared to be socially preening for about 4 minutes. They sat on two parallel branches and took turns gently inserting their beaks into the feathers on their chests and wings. Picture below. It appeared to be done with gentle care. I have plenty of pictures of the hawks “pecking” each other, but the because my data is in still photographs, this may hide a more gentle purpose. What is a peck and what is simply social grooming is very hard to determine with a still. I wouldn’t have quite appreciated that had I not witnessed this up there in realtime.
“Crop Limited Feeding:”
- The pattern by which the birds decide precedence in eating is difficult to determine, especially given the difficulty in consistently identifying which one is which. But there are some interesting observations still to be made:
- The turn a bird takes at feeding appears to be limited by crop size. A certain amount is eaten, and then the bird will – sometimes seemingly reluctantly – retire to the side unable to eat more. That is when another bird will hop over to partake.
- That transition is often done with seeming respect, with the next bird not immediately jumping into feeding, but moving carefully toward the prey item and waiting for the fed bird to move off a distance before eating. Once all birds have filled their crops, the prey may sit on the nest untouched for some minutes before one or another bird will decide they can take another morsel. Those post-feeding feedings are brief. See the 10 a.m. feeding on July 2 on what appears to be a woodpecker.
- Crop fullness is more difficult to determine as the birds age. When young, they are quite distended from the normal body shape, but as they age, this difference seems less.
- Barred owls can be heard calling in the past few nights. It’s been a while since we heard them around (briefly this winter, but with a dry spell of about 24 months prior to that, ever since the locals probably starved in the deep snows 2 winters ago).
- I’ve been shooting with a wider lens in the past few days, as focusing on the nest isn’t too fruitful, now that the chicks are flitting from branch to branch. For three days I shot at about 200mm (full frame), and today I put up a crop sensor with a 100mm lens (160mm full frame equivalent). That means that the resolution available per bird is decreasing, as I have to have the images cover more real estate. Most of the people reading this email aren’t equipment geeks, so I’ll spare everyone, but I will separately write up a post of some best practices I’ve discovered (by doing everything various wrong ways the first few times).
- While the pictures show the fledglings conducting adult-like sleeping behavior at night, standing on one foot, with head tucked back, when they tire during the day, they like to lounge prone in the nest. I find that a little odd, and wonder if
that is a camouflage tactic that changes with the light.
- The fledglings do not have the same eating pattern as the adults. When left a largely-intact bird, they do not eat the head prior to the chest meat.
- Mantling in this nest wasn’t seen until July 2 (Day 30), where it occurred earlier and more frequently with the 2015 nest.
- Interesting behavior 11:58 7/2, fledgling drops food item to lower layer of nest, seemingly caching, although future access is doubtful. (Perhaps intended to drop completely out of nest? Or not to drop at all?) Then the bird proceeds to sleep above it.
- Six minutes after that, mother comes with more food, and this time carves it up. Odd that one item left uncarved, then one completely carved up. Different skill levels of fledglings?
- Flies cover remnant meat in lower layer of nest within an hour.
- Mother is coming with food about every 2 hours.
- Post prandial hopping and flapping/posturing is still prevalent, even as they’ve all fledged. This suggests it may have more to do with posturing than the flight preparation theory from the literature.
- Feedings are not identical times from day to day, or quantity of times.
The full Cooper’s series: