Thursday, February 23, 2012

Dan brings a mouse to SnowflakeWhile we wait to see whether M/D Decorah will lay a third egg, I thought I would blog a bit about one of our other nests. The owls at Valmont, Dan and Snowflake, nest in a nest box 260 feet up a smokestack at Xcel Energy's Valmont generating station in Colorado. Owls have big wide heads that swivel almost 360 degrees, huge forward-pointing eyes that excel at gathering light, compact beaks, plump bodies, facial disks, and wing feathers with loose barbs that allow them to fly very silently. Owls swivel their heads because they can't (unlike us) move their eyes.

The tufts of feathers on top of Dan's head are neither ears nor horns. Dan's ears are located under his feathers, at the side of his head, and the right ear is usually set a little higher than the left. Sounds from below reach Dan's left ear first, while sounds from above (including echoes) reach his right ear first. The difference gives him aural 'depth perception', which allows Dan to map sounds three-dimensionally.

Humans don't do this very well. If I'm at a concert, I know the direction the music is coming from, but not the height of the stage the band is playing on. Is it three feet high or five feet high? I need my eyes to tell me. Dan, however, can pinpoint the exact location of the band, or his prey, just by listening. Owls swoop down on their prey from above. Dan's ability to hear and map objects in three-dimensional space helps him catch his quarry in low light, heavy brush, and under snow cover - places where eyes aren't much help. Academically speaking, owls accurately localize both the azimuth (horizontal plane) and elevation (vertical plane) of the sound source. If you like to read about geometry, sound engineering, owl hearing, or awesome stereo setups, google that last phrase.

In addition to offset ears, Dan and Snowflake have facial disks. This concave collection of feathers acts somewhat like a parabolic microphone to direct sound to their ears. In the post on feathers, I mentioned that some birds use them to aid hearing. Owls and Harpy eagles both have facial disks and both hunt under limited visibility. Like other many animals that live in limited or low visibility conditions (catfish and star-nosed moles, to name two) they have developed ways to compensate.

So what is Snowflake and Dan's domestic life like? She incubates the eggs and he brings the food - primarily mice, voles, rabbit, rat, and bird. Although he catches it with his talons, he always carries it in his beak. We've seen Snowflake 'incubate' prey in cold weather, presumably to keep it from freezing, but they don't larder up like the eagles do. They lay two to three round white eggs and begin incubating them immediately after laying - in theory. Snowflake does seem to spend more time off the eggs before all of them are laid. When the babies first hatch, Snowflake and Dan spend a lot of time caring for them. However, as the babies become bouncy, rambunctious 'teenagers', both parents will spend more time out on the perch. The teenage owls act a lot like Sarah, Percy, and Bill in the book 'Owl Babies' - "...and they flapped and they danced and they bounced up and down..."

Like the eagles, owls mate for life - but, like the eagles, mates that die will be replaced. Owls are very territorial and will defend their territory against intruders. Several years ago, the nest box at Valmont was invaded by a strange owl. The two females fought quite viciously before one of them - we think the intruder - was vanquished. Dan and Snowflake have also driven off ravens, which can interrupt nesting, and incubated eggs through thick snowfall and icy rain. Like Bald eagles, they are well adapted to cold weather: they even have feather feet to help protect against cold weather and possibly to sense prey.

2011: The Owls Face A Crow

Dan and Snowflake laid the first egg on 02/13/2012. I estimate first hatch on March 10, although it could be a little earlier or a little later. Xcel Energy has still photos of the pair now and should have the streaming cam back up shortly. You can watch them at our website: http://www.farmyou.com/falcon_cams/index.html (click 'Xcel Valmont Owl Cam') or at Xcel Energy: http://birdcam.xcelenergy.com/owl.html

Information from this post was taken from Collin Tudge's 'The Bird' and the following websites:

6 comments:

Katharine said...

Thank you, Amy, for all the great info.

DotK said...

Great info, Amy. First egg for Snowflake this year is 2/11.

Penny said...

Thanks, Amy! I loved the read.

Bob said...

Great blog on the owls Amy. I have a pair of GHOs nesting in my backyard and my observations of them confirm your info except that my owls do "larder" prey items in trees near the nest when the owlets are growing rapidly and retrieve them to feed owlets during daylight hours.

Keep up the good work.

Bob in Alberta, Canada

Amy Ries said...

Thanks, Dot - keep meaning to change that! Bob, that is interesting information. These guys are on a smokestack, but there are still places they could stash prey out of sight.

Dot said...

Hi Amy - I think the oldest owlet - who we called Meester Beeg - fledged on 4/30 - at exactly 6 weeks old.