Thursday, March 15, 2012

Peregrine Falcon FAQ

While we wait for eggs to hatch in Decorah, Valmont, and Fort St. Vrain, I thought I would talk a little bit about Peregrine falcons. Prior to the Decorah Bald eagle cam, Peregrine falcon recovery was what we were known for, to the extent we were known at all.

In Flight
The Peregrine is the fastest animal in the world, diving or stooping at speeds that can reach over 200 miles per hour. Almost everything about it is built for speed, from the baffles in its nose  to the jagged edges of its slim, stiff feathers and long, pointed wings.

The falcon catches other birds in flight by diving on them from above.  As she begins her stoop, she rolls, cups her wings around her body, and tucks in her feet. This change in shape streamlines her profile, yielding an aerodynamic raindrop that can cut through the air at high speeds.
Photo used with permission of Karen Carroll, http://www.birdsofprey.net
As she plummets her nictitating membrane, a transparent 'third eyelid', protects her eyes from dust and debris in the air and a secretory gland helps keep her corneas from drying up. A special cone or baffle in her nose regulates the amount of air entering her nasal cavity, allowing her to breathe and protecting her from damage. A curved flight path keeps her prey in view and reduces her aerodynamic drag. Before she strikes her prey, she'll experience G-Forces estimated at between 25-27 Gs.

The Peregrine meets her prey feet-first. She slows first, unfurling her wings and tail, and dropping her feet. After striking and stunning or killing it outright, she'll loop around in mid-air to retrieve it and take it to a safe place for plucking and eating.  
Falcon Belinda at Xcel Energy's Allen S. King plant aims at a reporter.
Lifestyles of the Fast and Furious
Falcons are roughly crow-sized. Females are about a third larger than males, although they both have bluish to slate grey backs,  barred or streaked white to rusty underparts, and a black hood. Adults have black beaks and yellow feet, although their babies may initially have bluish feet.  This is natural and not a cause for alarm.

Both males and females are highly territorial. Like eagles, Peregrine falcons are relatively monogamous (polygamy has been documented, but isn't common) and may or may not migrate. Unlike eagles, they are relatively solitary birds.

Traditionally, Peregrine falcons nest on cliffs, laying their eggs directly on a scrape they created in a gravel or sandy substrate.  In the midwest, Peregrine falcons generally:
  • Lay eggs in late March or early April
  • Hatch in late April to early May, or 33 days after the first egg is laid.
  • Begin flying in mid-June or later, or about 40 days after hatch.
Peregrines make excellent, attentive parents. The babies cannot thermoregulate (control their temperature) until they are about 10 days old, so Mom spends a great deal of time huddling over them while Dad feeds everyone. As the babies age, both parents spend time hunting. The eyrie is small and the babies, which have among the fastest growth rates in the animal kingdom, are large and hungry. They eat, sleep, poop, and go from white fuzzballs to sleek brown juveniles in about five weeks.

Once they begin flying, the young peregrines spend a lot of learning how to fly and hunt: something that looks a lot like play to most human observers. Their parents will continue to provide some food for their newly fledged young who are not yet self-sufficient.  Come fall, the adults may or may not migrate, but their children will disperse. In our experience, the young falcons tend to leave in September. Once they are gone, they are gone. If they do come back to the nest, their parents will defend it from them. 

What to expect when falcons are expecting
The new Great Spirit Bluff nest cam wonderfully documented falcon courtship. The falcons engaged in  ledge displays on the roof of the nest box, bowing and calling loudly.


As courtship progressed he made a scrape, digging into the gravel with his breast and pushing with his legs to create a depression (males and females will do this - our video shows the male).


Finally, both falcons bowed and e-chupped over the scrape.


The male also courts the female with food. Our video shows him bringing it to the nest box, but falcons also transfer prey midair. There seems to be a little bit of food fight here as well, but think some courtship was going on.


She will probably lay three to four reddish speckled eggs sometime in March. Peregrine falcons do not begin full incubation until after egg number three is laid, so it is normal for her to spend time - even quite a bit of time, depending on how warm it is - away from eggs number one and two. Her eggs should begin hatching 33 days after the third egg is laid.

Mae's eggs, Xcel Energy Allen S. King Plant.
Some egg color variation is normal.
During incubation, she will experience hormonal changes that help keep her incubating. She may appear sleepy or lethargic, and will spend a lot of time picking at gravel and sitting more or less quietly on her eggs. She does most of the incubation, although the male will spell her briefly. The male is smaller and may have a harder time covering all of the eggs, depending how many are laid. We can also expect to see egg rolling (Brent, at the Allen S. King plant, is well-known for this) and some shimmying. This is not a particularly active time for the falcons: I've heard Bob refer to incubation as the 'egg doldrums'.

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