Saturday, May 28, 2011

We have lift-off .... to the ledge

After a couple of days of looking, leaning, but not leaping, two of the eyasses finally got brave yesterday afternoon and made it out to the ledge.  Thanks go to Carolyn Sutton who raced down to the nest to get these pictures.  One small step.....

After about 45 minutes on the ledge, both eyasses safely clambered back up into the nest.

Here are some of Kay Meng's pictures from Thursday in the Board Room.  We are in the midst of summer's first heatwave in Philadelphia with temperatures in the mid-90s.  The eyasses were clearly feeling the heat, panting with beaks agape and tongues held high.

They kept sitting back stretching their feet to gain more surface area to dissipate heat.  Those talons, as yet unused, are already formidable weapons.

Their eyes are starting to turn gold, though it is still more of a gray-gold than the characteristic yellow of fledged eyasses.

The feathers are coming in strongly on the wings, but have a long way to go until they can safely fly.

You can see in the image above how the feathers have not yet fully emerged from the feather sheaths.

John Blakeman shared some information in a previous year's blog post about the importance of feather development for the eyasses' safe fledging when that time comes:

"Everyone has noticed how much time the birds spend 'preening,' tucking their heads down into their feathers. In fact, they are using their bills to strip off the drying feather sheaths, allowing the growing feathers beneath to emerge. The feather sheaths still remain at the base and shank of the larger feathers which are still, as we say, 'in the blood.' As the feathers grow out, they actually have blood vessels within, nourishing the growth of these miraculous body features. So, for a while, heavy blood remains coursing through the big tail and wing feathers. Until this ends, when the bird is 'hard penned,' the wings are a bit heavier."

Here, on the left you can see the sheath at the top of the dark feather.

As always, there were various body parts of prey lying around the nest which, because of the hot temperatures, were attracting a considerable number of flies.  The eyasses were very interested in these flies, watching them intently.....

... and snapping at them when they got close enough.

They also watched Kay with enormous curiosity whenever she changed cameras or lenses!

Much as I love these eyasses, I have to say they are currently in a rather unattractive stage of their development.  Long gone are the adorable white fluff balls.  These guys currently look like badly designed vultures!

But the gorgeous chestnut-peach plumage that will eventually cover their chests is starting to become apparent.

Also growing fast are the white "pantaloons" on their legs.

Here, on the eyass in the background, you can see the 36 hour difference between the third to hatch and its slightly older sibling in front which has more feathers showing on its head.

As the afternoon progressed, the eyasses settled into a panting torpor.

 The haggards never appeared on the nest, though we did see a couple of fly-pasts.

LATE BREAKING NEWS!  The Franklin Institute has switched to their other camera so we can now see both the nest AND the ledge

Thank you, Franklin Institute - you're the best!

Monday, May 23, 2011

Sunday morning with the hawks

On Sunday morning, Kay, Caroline and I met down at the nest to check out the eyasses from the ground up.  It was good to have Kay's trusty lens back in action!

It was pretty quiet at first with only the occasional bobblehead peeking out at us like a fluffy periscope.

Gradually they became more active...

... and we were treated to some vigorous wing flapping.

The formel flew in with breakfast...

...and scrutinized us with that laser stare.

This is a good view of the stripey markings on her chest...

.... in contrast to the tiercel's spots.

The formel then left the nest for their favorite tree about 50 yards away across the Vine Street expressway.  She perched on the topmost twigs which swayed perilously under her weight, but she seemed quite unconcerned.

The tiercel paid a short visit to the nest...

... and then headed out to hunt...

... leaving his offspring to continue their peaceful Sunday morning.

Friday, May 20, 2011

Why don't the eyasses fall off the edge of the nest?

 As the eyasses become increasingly curious about the world out there...

... nervous nest watchers worry as they see the eyasses move closer to the edge of the nest.

Each day, there is more wingercising...

... and scary losses of balance right at the edge of the nest, four floors up from the concrete sidewalk of Winter Street.

Experienced Franklin Institute nest watchers have lived through this twice already, and know that the eyasses manage to stay safe.  I asked John Blakeman why this is, and he shared this fascinating information:

"Actually, the little eyasses have a pretty developed and strong impulse to stay down in the bowl of the nest. They don’t rationally know that they sit precariously at height in a tree or on a ledge. But instinct and natural selection have left them with good instincts regarding the hazards of getting too close to the edge of the nest.

However, Red-tail eyasses do sometimes fall out of the nest, but almost always during defecation. It goes like this - unlike passerine birds (“song birds”), Red-tails and other similar raptors do not excrete fecal sacs. These little bags of feces are lifted out of the nest and carried away by the parents. This keeps the nest clean, and reduces the discovery of the nest by marauding predators such as raccoons who would prey upon the nestlings if discovered by olfactory hints.  But in Red-tails, the little eyasses have an instinct to, as falconers and raptor biologists say, “slice.” Watchers of the eyasses in The Franklin Institute nest have seen this. The little eyass stands and backs its tail out toward the perimeter of the nest. Then, in an instantaneous spurt, the eyass squirts the “slicings” out over the edge of the nest.

But very infrequently, the little eyass backs up too close to the edge of the nest, and simply falls out backwards, all in the good attempt to direct its slicings away from the nest. Frankly, I’ve never encountered this, but it has been reported. I think that when an eyass falls from the nest during slicing, it may have some neuromuscular difficulties. It happens, but rather rarely. We needn’t concern ourselves with it. 
A word about the “slicings.” In defecation, hawks and eagles are said to “slice.” The feces are “slicings,” and the remnants in the FI case are seen as the white stains on the lower edge of the window. Our three eyasses have nicely sliced on that surface.

 They have also sliced on the wall alongside their nest.

But things are a bit different in true falcons. Falcons don’t slice, they “mute.” Falcons are unable to powerfully project their feces (called “mutes”). Instead, a defecating (“muting”) falcon merely drops her mutes beneath her. This has significant results at falcon aeries [nests], which are almost always on a ledge or cliff. 

Falcons are known to occupy aeries for literally centuries. There are Peregrine Falcon aeries in the UK that have been occupied since the Middle Ages. Actually, they have probably been occupied for millennia, since the ending of the Ice Age. 

How do we know this? Well, there is the historical record of falconry, where British and Scottish falconers have been taking eyasses from these nests as long as falconry has been in the British Isles, probably from the ninth century or earlier.  But these piles of falcon mutes tell their own story. The same phenomenon occurs in American Prairie Falcons, in the West. Out there, raptor biologists have bored down through many feet of ancient Prairie Falcon mutes and have counted the layers (a new layer each year). Some of these aeries are centuries old. 

A falcon can get away with this, as mammalian predators of eyasses such as raccoons, weasels, badgers, and the like, can’t climb around on steep, high cliffs. The eyasses are safe, even though their aeries can be easily spotted from afar. Falconers and raptor biologists scan the long streaks and thick deposits of falcon mutes, the “hawk chalk.” I’ve spent five summers in the West studying raptors out there, and finding a Prairie Falcon nest was not very hard. Just scan a long cliff face with a pair of binoculars and look for the white hawk chalk. Very obvious. (And obvious, too, to the falcons. New aeries have been created by merely painting white hawk chalk-like streaks on an empty cliff ledge. Within a year a pair of Prairie Falcons will often take up residence, subsequently creating their own hawk chalk.) 

About raptor feces. Hawk slicings and falcon mutes are predominantly white, with a central blob of darker, more consolidated material. The white, liquidy portion is primarily uric acid, a concentrated form of the liquid, dissolved urea found in mammalian urine, including us. We, like most mammals, both urinate and defecate. Not so with birds, especially our hawks and falcons. Instead of clearing waste proteins and other nitrogenous materials with water and dissolved urea (from the kidneys), birds can’t be carrying around ample amounts of water to make urine. Instead, they further process the urea their livers create into concentrated white crystals of insoluble uric acid. That’s the white part of the bird’s splat on a windshield. It’s concentrated, so as to use very little water. 

The dark part of a mute or slicing is actual intestinal feces. Because raptors very thoroughly digest their food, and there is no “fiber” content, there isn’t much left coming out of the intestines after digestion. Most of what raptors eat is bone and protein. Hawks and falcons (unlike owls) thoroughly digest all bone material, so there is no solid bone waste in the mutes or slicings. The proteins of the prey are completely digested and eventually end up as the white uric acid — except for feathers or fur, which is not digested but vomited up each day as a “casting,” or “pellet.” Castings are the balls of fur or feathers from the previous day’s meals, expelled through the mouth.

Well, I guess I’ve pretty much sliced up all of that. I’ll now go mute.

–John Blakeman

 While John is mute, here are some pictures from this week at our nest.

The eyasses still take long naps, sometimes spread out ....

... and sometimes in a cosy clump.

 When they are awake, they are on full alert.  Here, the tiercel (dad) has just flown off the nest, and they are intently watching him as he flies across the Parkway.

John Blakeman tells us that "honing visual acuity is one of the very important maturation processes that the eyasses are learning while "just sitting around on the nest." This ability to follow distant objects moving in the landscapes these hawks live in is a crucial survival lesson. The FI eyasses are learning those ocular and neuromuscular skills now. They are learning to visually follow food, something that will allow them to follow rats and mice when they start to hunt."

The following are pictures I took through the Board Room window with a point-and-shoot camera, so the quality is nowhere near that of Kay's pictures, but it gives a sense of their growth, and also of the surrounding landscape.

Here's the formel looking out across Winter Street and the Parkway with the Vine Street Expressway running underneath.

She sees everything, and here she is keeping a very close watch on a passing dog walker.  You can see how huge the eyasses' feet are.  They have to keep them arranged out in front so as not to tangle in the nest sticks!

The formel is a very intimidating bird up close.  I was glad the window glass is thick.....

The eyasses' wing feathers are starting to grow through their fluff...

... and the characteristic chestnut and black banded tail feathers are apparent.  The red tail feathers do not appear for the first two years.

That bobblehead has a serious beak!  Their eyes are currently jet black, but by the time the eyasses fledge from the nest, their eyes will be a lovely gold in color.  The eyes turn back to black when they are mature hawks.  Golden eyes are a clear indication of an immature hawk.

The eyasses line up nicely while mom picks off tasty morsels for them...

... and there is no squabbling as she feeds each one.

After eating, they settle down for the afternoon, but it is not long before this eyass decides to play tug-o-war with a rat carcass, yanking on its tail.

They are intensely curious about what is going on behind the window, showing no fear whatsoever.

The tiercel flew in and joined the family for a quick visit.  He is noticeably smaller than his mate, and though he is a stone-cold killer, he has a gentler face than the formel.

 He brought a nestling - looked like a young robin - pulled it apart, and enthusiastically fed the eyasses.

 The nest now has three year's worth of sticks and towers above the wooden frame that the Franklin Institute installed after the haggards' first few attempts at a nest kept blowing off the ledge.

And so ends another great week for the eyasses and their parents.  Let's fasten our seat belts and have the valium on hand for when they start hopping and "catching air" and heading out to the ledge!