Thursday, September 02, 2010

Where Do the Young Red-tailed Hawks Come From in Winter? The Views of Readers and Mr. Blakeman

Photo: Donegal Browne
The matter in question is what are the chances of survival for the Riverside young who have fledged so late in the season? Plus just where do all those juveniles come from who winter in Central Park and the other smaller parks in NYC? Are they local? Migrants?

From Anonymous in the comments section—
I'm curious as to why this year's babies would get a migratory urge. Last year's Riverside baby certainly didn't. Even if the birds aren't as adept at hunting as they might be, won't they realize that prey is all around them, and keep trying? Would their instincts tell them to leave an area which is rich in prey?

A happy addition to my previous comment: one of the Riverside babies caught a mouse today. Perhaps we have precocious youngsters.

Everyone is curious as to why Mr. Blakeman thinks these babies will migrate. We are used to seeing juvenile hawks here in winter, and the assumption is they are here because food is plentiful.

From Sally of Kentucky—
Of course I hope Mr. Blakeman is wrong, but of course I also know he is not, especially if the birds migrate. Your question is a good one-does the abundance of rodents and pigeons in NYC year round improve the chances that the young would stay and survive in the city? Rat poison aside that is. :( Not all juveniles leave the city, as you noted. We have seen Pale Male Jr and Charlotte, who appear so like their alleged parents, and we like to think that many of the hawks in the city are progeny of Pale Male. No one knows, obviously, and do we even know if they were born in NYC, did they migrate and return or winter over? Interesting indeed.

From Karen of Rhode Island
I am pulling for the Riverside babies surviving. They have already fledged, according to Lincoln's website.

Remember when their Mom was not supposed to be able to feed them because of her damaged beak? Yeah, Riverside hawks!

From Jeff Johnson

Ms Browne,
It's not such a stretch of the imagination for the late season Redtail fledges to winter in NY and take advantage of their parents continued help while taking advantage of abundant prey during their hunt training. My big fear is that they'll eat a poison tainted rat.

From Erik Sweig of NYC

I submit that the adaptable Red-tailed Hawk as a species, may have more choice in the matter of migration, or be spurred into migrating or standing pat by not only an urge but mitigating circumstances such as hunger or a high prey base.

My question for John Blakeman --

We often have quite a few juveniles overwintering in Central Park, where do you think they come from? Couldn't some be local young that have found the Central Park raisin in the raisin bread compelling and have decided to stay? I suspect rats being rats that there are new inexperienced ones being born just about all the time.

And his response to me--

The question of the origin of winter immatures, whether in Central Park, or here in northern Ohio is has the same unknown answer. I have a sneaking suspicion that these are birds from the north, who found prey on their way south and stayed around for the winter. I really think that the migratory urge is pretty strong for first-year red-tails and they really start to move in late September and all through October.

So in my area, I think most of my winter immatures were hatched in Michigan, or across Lake Erie in Ontario (although red-tails NEVER migrate straight across the lake. They cross the Detroit River and drift down the western shore of Lake Erie and then disperse E and W across Ohio when they hit Toledo.

The Central Park winter red-tails probably drift down from New England, or down the Hudson from Ontario, Quebec, and upstate New York. It's the rats that hold them there, surely.

--John Blakeman

After a good number of years of NYC hawkwatching and then comparing the behavior of urban hawks with those of rural hawks in Wisconsin for a couple of seasons, I've got some thoughts myself but I'm going to delve a little deeper first before expressing them while we all digest today's comments.

Anyone with other thoughts or other information please dive right in.

Donegal Browne

Tuesday, August 31, 2010

Hurrah! Another Young Chipping Sparrow and Blakeman on the Riverside Fledglings Chances This Late in the Year

As you may remember I had been concerned that the local Chipping Sparrows, who raised a bumper crop of Cowbird young with none of the own chicks surviving this year at a certain point, would have nothing at all to show for their hard work when it came to offspring of their own species for the season.
A month ago I was heartened to see a young Chippie being fed by a parent and again today to my relief yet another youngster was out on the feeding floor being fed.
By nesting yet again precariously late in the season for Wisconsin, after the Cowbirds had already left the area, they were able to have success. This juvenile, and likely nest mates I've not seen as I was among the missing for several weeks and Chipping Sparrow fledging tends to be rather staggered here, all will all have lost their baby streaks and will be feeding successfully on their own by the time they'll need to migrate. I believe that abundant food from feeders helps to make this possible.
Next up, longtime reader Betty Jo of California who'd been following the second nest of the Riverside Hawks who are just now fledging very late in the year, sent in a question for Red-tail Answer Man John Blakeman--

"I am wondering how the Riverside babies can learn to hunt before winter sets in.
If they lived in the south I guess it wouldn't be such a problem. What does John have to say about these late bloomers?"
And John Blakeman's answer--


The prospects for this pair of eyasses is extremely low, perhaps close to zero. Everything is against them, particularly time.

They will be off the nest in the next week, it appears. But unlike eyasses jumping off in June, these birds will not be able to find populations of young, weak, and inexperienced offspring of other species to learn to hunt on. By now, all the potential prey animals out there are strong and experienced. Finding enough weak, young, or vulnerable prey is going to be very difficult.

Of course, for a few weeks, the parents will be dropping rats and pigeons they capture for the eyasses. But those provided food items only keep the eyasses alive. They don't allow them to learn how to hunt and kill for themselves. That's the crucial factor, which usually takes all summer to effectively learn. These birds don't have three and a half months of summer hunting to learn to be self-providing predators. At best, they will have, say, six weeks or less to learn how it's done.

By late September, with rapidly declining photoperiods (daylength), the birds will get a strong migratory urge, and get up in a warm thermal and start drifting south at one or two thousand feet. In an hour, they will be south over New Jersey drifting along with the dozens of other red-tails trekking south from New England or the coastal regions.

Then, they will get hungry, and hunting and migrating are two, conflicting urges, ones that they will not much know how to deal with. Mostly likely, they will end up starving somewhere south of New York, perhaps in the Pine Barrens of New Jersey (as this would appear, correctly, from the air as having prey animals), or perhaps much farther south. But even if they could find an area packed with voles or other common prey, these hawks simply have no experience in consistently capturing them. All might be well when the weather is favorable. But what happens when an autumnal two-day rainstorm hits them on their way south? That is likely to start a fatal cascade of events leaving them dead by starvation in a hidden field somewhere to the south.

So, as excited as everyone was with the remarkable re-nesting of the adults of this pair, after the earlier nest and eggs were blown out of the nest tree by some powerful winds, I recognized that the prospects for the eyasses after a late-summer fledging were very poor. I wasn't very excited by the requisite difficulties these birds were to face. Those are now all close at hand.

Even with everything normal, first-year red-tails have at least a 60 to 80 percent first-year mortality. Only one or two out of five will survive the first year---and it's probably even lower than that.

The parent haggards were exceptional in their urgency to re-nest, and they did well. But their eyasses won't, sadly. Time and experience are stacked against them.

By the way, I've never seen a successful re-nesting such as this out here in wild, rural northern Ohio. There just isn't enough prey to support such an effort, not enough proteins and lipids to allow the formel (female) to assimilate a second, complete clutch of viable eggs. In honesty, this all happened because of the abundance of rats in NYC. (No offense intended.)

--John Blakeman

And then I had a question and a thought--

We often have quite a few juveniles overwintering in Central Park. Where do you think they might come from? I’ve always thought they might be local young that have found the Central Park's status of a raisin in the raisin bread compelling and have decided to stay.
I remember Stella and I watching two adult hawks flying with two juveniles, circling together in a friendly manner over the park, very late one year, possibly even early December. I suspect rats being rats that there are new inexperienced ones being born in CP just about all the time.
What do you think?
Donegal Browne

Sunday, August 29, 2010

A Wing-tip Kiss of Newly Bonded Canada Geese?

It began commonly. It began with an event which I've seen many times, often daily during this season, which had never produced anything that I'd not seen many times over--the arrival of a large flock of Canada Geese to forage in a newly harvested grain field.

I watched which field they were circling toward and when I happened to be over that way for a few minutes, there they all were-- eating, taking turns playing sentinels, and all the common things that Geese do in this situation.

I then went off to look for turkeys or maybe cranes. Finding neither, and loosing the light rapidly, I started taking photographs of people working on their machines which took me back toward the south field where the flock had originally lighted.

And what should I find? No flock at all. Just two geese who for whatever reason seem to have stayed behind and not immediately gone with the group. Two geese, who are mimicking in an odd way, the behavior of Spring. The goose is sitting in a somewhat hidden spot while the gander stands tall looking for possible interlopers, raiding raccoons, stupid humans, and all the other things that put eggs in jeopardy. But it is nearly September therefore I can't imagine there being eggs for the goose to sit on. Though in nature one does learn to never say never.and to watch and wait for a possible explanation, one being, though still on the bottom of my list, that there really are eggs over there.

I watched for a few minutes. They watched me and not wanting to disturb them, I walked off to try to get some shots of the setting sun glinting off some steam engines.

If Goose is sitting tight after true dark I'll have to rethink the egg theory positioning on my imaginary list.

Whoosh, suddenly they took to the air with synchronized wing beats and began to fly my way.

The front goose begins to honk and the trailing goose rises and flaps faster.

And then it happened--the lower goose had her wings on the up beat, and the higher goose on the downbeat. The tips of their wings touched, they broke flap stride, took a beat with wing tips just meeting, in a light as a feather, (sorry) moment of unusual glide. Then they separated and flapped off to where ever they were going.
Is this some sort of goose bonding behavior for young unbonded birds in the Fall? An accidental aberration of some kind?
Has anyone out there ever seen it happen?

Donegal Browne