Do Very Young Red-tailed Hawks Get the Migration Urge? For That Matter, What About the Adults?

Photo: July 24, 2005 D.B.


Little on fledge day-- one of a pair of young from Charlotte and Pale Male's second clutch of that season.


An Update from Riverside Hawkwatcher Pam Langford--

More good news -- one baby caught a pigeon today! The worrier in me hopes it wasn't an easy catch because of disease. Interesting discussion about migration.


Pam,

Many thanks for the update.

Indeed, one hopes it wasn't disease though disease isn't as likely as it might seem. Except for frounce which doesn't really affect an infected pigeon, many common pigeon diseases, such as polymiosis virus (PMV), which adversely affects a pigeon's nervous system making them easier to nab, aren't communicable to hawks.

From my contacts with the pigeon folks in NYC, there is some PMV birds out there right now. It's most common in warm weather. On the other hand, the Riverside parents may just have trained their youngsters well and this fledgling is an ace.

Best regards,
Donna

And the next day a second email from Pam concerning John Blakeman’s prognosis for the Riverside young--

Mr. Blakeman said that the urge to migrate in juvenile hawks is triggered by shorter days. Do we know how a juvenile hawk's age might affect this response? After all, the Riverside babies are younger than most Red-tails are when September rolls around. I wonder if their age means they won't respond to the same cues that motivate older juveniles because they are at a different developmental stage. Since what happened at Riverside this year is unusual, it's possible that no one knows the answer to my question.

Thanks again for this interesting discussion. By the way, hawk watchers at Riverside yesterday were treated to the sight of a visitor. A swan was making himself at home in the marina! I've never seen that before.

Pam





I've done some searching and haven't found a study on late second clutch fledglings and migration so we'll have to go with the limited anecdotal information we have from observation and possible comparisons with other species.



By the way, one or both of the Riverside Fledglings appear to be precocious hunters-first a well hunted mouse and then a pigeon. We've rarely seen this much successful hunting this early in maturation in a young urban Red-tail's life.



John Blakeman has told us about the phenomenon in rural hawks when the young are sometimes chased from their parent's territory. The thought is that the young are pushed out of their natal territory when the prey base has become thin or when it is time for the parents to begin their yearly courtship behavior.



As far as I know, we've not seen this in an urban environment and I've only seen one case in rural Wisconsin. Some years ago in mid-winter I saw a pair of Red-tailed hawks chasing a brown-tail, who looked remarkably like them, (albinistic characteristics) in circles through the trees in a small area. Finally the young hawk was chased and knocked off branches enough times that he at least flew across the road into dense branches, followed closely by the adults, where I could no longer observe their behavior


Though I can't absolutely swear that this young hawk was the progeny of the adults of the territory, I would argue strongly that they were the parents of the young hawk from the observations of their physical characteristics. Therefore we could hypothesize that this young hawk had not migrated in the Fall and it therefore follows that not all first year hawks do migrate or at least don't go very far from their natal territory.



And if that is the case we've no absolute reason to believe that hawks that are so endocrinalogically immature would absolutely respond to the shorter photo period hormonally produced migration urge and whip off to parts unknown.

And another point for thought from NYC Bill from the comments section--
As an ex-NYC tour guide who used to ride around on a double-decker bus pointing out the sights, I was often impressed by the fact that the 927 hawks (PM and Lola) never seemed to go anywhere except across the park to the Beresford (next to the AMNH) for the winter. And that was to the west. I guess I supposed that RTHs didn't migrate very far at all... if ever.



Previous hawkwatchers have reported that some earlier mates of Pale Male had "disappeared" in the winter and returned in time for the yearly courtship and bonding rituals of Red-tailed Hawks. In one mate's case, if the person who purportedly found the deceased mate and her band is believed, she'd only gone across the river to New Jersey, conceivably back to winter in her natal territory.



Pale Male has been closely watched since he arrived and doesn't appear to go anywhere in the winter and never has. He hasn't migrated, even as a Brown-tail. He did have to come from somewhere though as there were no observed nesting Red-tails in Manhattan previous to his nest for a hundred or so years. (Unless of course some pair nested off the birdwatcher radar in Manhattan or he only made a short hop across the river from Jersey, hardly counting as a migration from my definition.)Though as was said, some of his mates seem to have left for the winter. Lola on the other hand, no matter the behavior of her predecessors bides her winters with Pale Male in Central Park.

But what about all those hawks that fly by Hawk Mountain every year?

This is when I had to go back to do even more delving. Sorry it's taking so long. There is a lot out there, but very little of it specifically pertains to the question that we have on the table--specifically urban hawks and migration habits.

It hit me. Wait a minute-- I think I know the definition of migration but let me look that up.

Ah ha! From The Earthlife Web--What is Migration?
"In everyday speech migration is regarded as the mechanism behind the seasonal appearance and disappearance of some species of birds, mammals, fish and insects. To most people migration is birds, and perhaps mammals. Though in fact many insects, some mites and spiders, some reptiles, amphibians and even plants migrate regularly. Here we are concerned with the migration of birds.

A more exact definition of migration is the mass intentional and unidirectional movement of a population during which time normal stimuli are ignored. This allows migration to be distinguished from dispersal. Dispersal is multidirectional, often only involves part of a population and does not involve the ignoring of normal stimuli."

And there we have it.

Red-tailed Hawks, at least the Red-tailed Hawks I'm familiar with do not migrate. They disperse. And then only sometimes. When it comes to dispersal there is a choice and various stimuli can affect that choice. For instance your parents run you out as food is getting scarce. I've seen it in Wisconsin but never in NYC.

Plenty of food, plenty of unclaimed territory near by? Why go further?

There is also the possibility that one of the reasons that individual hawks become urban hawks and start a line of urban hawks is because they have a low urge to disperse, perhaps we could say, they genetically just have less wanderlust as adults and therefore may have less as immatures. Plus they are genetically capable physiologically of becoming human habituated.

A little like the wolves ages ago who were capable of becoming human habituated genetically and eventually evolved into dogs. And at least with dogs it's believed that taking this path had much to do with their endocrine systems. Hmmm.

And the endocrine system in birds has much to do with migration.

Of course even rural Red-tails sometimes stay around as they are responding to normal stimuli. "Lots of food, not that cold, snows not deep, guess I'll stick around."

Red-tailed Hawks can make a choice. Therefore my hypothosis is that some of those juveniles in Central Park are local.

In order to prove my hypothosis, the young urban hawks would have to be banded and itb is my understanding that at least in Central Park and perhaps any number of other NYC Parks there is no banding allowed.

Donegal Browne

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.
Jeff

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--
Donna,

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

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--

Donna,

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