John Blakeman offers the following helpful advice on this topic, and
asked me to pass it along. How much trouble would it be to report age 
classes of raptors?
Bill Whan, Columbus
p.s. Also below, after his contribution, I send along a recent bird 
report from the UP, which is relevant to the raptor discussion and has a 
lot of suggestive latitude-related information.


As a master falconer (flying red-tails) and life-long Ohio raptor 
student (formerly banded, re-habbed, etc.), I have several observations 
regarding the reported reduced numbers of Ohio winter raptors.

First, regarding rough-legs. Their irruptions out of Canada are almost
exclusively related to the state of lemming and other small rodent
populations.  When these are high, as apparently now, there is no hunger 
motivation for the birds to move to more wooded lower latitudes. This 
year, small rodent populations must be adequate in Canada, holding these 
hawks at higher latitudes.

The converse can be said for red-tails. Now Ohio doesn’t have lemmings, 
but  meadow voles (Microtis pennsylvanicus) are the sustenance diet for 
most winter red-tails in Ohio. Yes, experienced adults can persist on 
other prey, but  the larger portion of the population requires adequate 
voles to survive the  long, cold winter Ohio nights. To the south, it’s 
not as cold, nights are  shorter (allowing longer daylight hunting 
periods), and most importantly as  shown in this year, there is reduced 
or absent deep snow cover.

And that can be the deciding factor retaining or pushing many, perhaps 
most  winter red-tails out of the state. This is particularly true for 
immatures and  unmated, inexperienced young adults, the so-called 
“floaters.” These birds have  not bred and have no mates. They are not 
attached to any particular winter  territory.

All of these birds, immatures and unmated young adult floaters, are free 
to  wonder around the winter landscape looking for good vole habitat. 
That’s exactly  why so many are seen at all the usual spots in winter, 
such as Killdeer Plains,  where voles abound. Likewise when seen sitting 
on fence posts and utility poles  along larger grassed highway margins. 
Lots of voles are easily captured at these sites.

But, in winters like this, where deep (>3 inches) snow persists for 
longer than a week or so, and when nights are particularly cold, winter 
resident immatures and floaters quickly get in trouble. The voles run 
safely in their  sub-snow runways, utterly unseen by any hawk perched 
above. Immature red-tails  are particularly inexpert in capturing larger 
prey, a factor we falconers know  first hand. After a year of chasing 
cottontail rabbits, they become expert in taking these larger animals. 
But a new immature red-tail sitting out on an Ohio Interstate looking 
for snow-obscured voles gets hungry in a few days and must  then start 
chasing what few larger animals it can find.

Most learn quickly that this won’t keep them fed, and two things can
happen. A good number become migratory once again and start
drift-hunting on the way south, looking for some non-snow vole habitats 
somewhere to the south. Sadly, a good number simply starve to death. 
Once adequate fat reserves have  been depleted by a week or so of the 
very cold weather we had in late December  and early January, the 
now-weak hawk can persist only by metabolizing muscle. That’s a 
metabolic cascade that in a few days ends in death.

Falconers are familiar with all of this, and take exquisite pains to 
keep their birds from ever approaching this lethal weight-loss 
precipice. Wild winter  red-tails have no such nurses or hunting 
mentors, causing the large winter die-off of these young birds.

I would add parenthetically that the birding community could contribute
markedly to a quantitative understanding of this phenomenon, if they
were to be diligent in tallying both adults (with red tails) and 
immature (with non-redtails). Sadly, only total numbers of these hawks 
are commonlyrecorded, presuming that a hawk is just a hawk.

That’s not so this winter. The adult red-tails I study in my area of
northern Ohio (Erie and Sandusky Counties) have not declined this
winter. They can handle anything nature offers here. But yes, most of 
the immatures hanging around the Sandusky Bay habitats (Resthaven 
Wildlife Area, Pickerel Creek Wildlife Area, Willow Point Wildlife Area, 
Blue Heron Reserve, many others) are depleted. The deep, persisting snow 
and cold have killed them off, or moved them (probably only a few) way 
to the south.

Biologically (Do birders do biology? Sorry for asking that contentious
question—just for prompting in this particular matter.) it would be so
wonderful  to have adult to immature red-tailed hawk ratios in autumn
migrations and winter residencies, compared to those in the spring 
migrations. The helpful statistical analysis that such data would 
provide is too detailed to describe here. But a  few years of such 
tallies would allow a very accurate understanding of the age  structure 
dynamics of red-tails in Ohio. From these birder-provided data, we 
could begin to quantitatively understand what ratio, or even pure 
numbers, of red-tails die each winter. Simply compare autumn and spring 
migration adult to immature ratios. Right now, these numbers are
meager, if non-existent.

And the same thing should happen with bald eagles. The ratio of adults 
to immatures is markedly changing as the population expands and adapts 
to new habitats and prey. But mere specimen counts lend no information 
to answer these biological questions. Expert birders could provide 
helpful information if they’d start listing both immatures and adults of 
raptor species for which this can be  so easily determined. Just how 
difficult is it to see a red or brown tail, or a white or black head?

–John Blakeman

+++UP Rare Bird Report for January 15, 2009

The month of December was mild, and many bodies of water remained open,
allowing a number of lingering waterbirds including ducks and grebes to 
be recorded later than usual this season. It has been a decent winter 
for over-wintering hawks in the UP. More Cooper's, Sharp-shinned and 
Red-tailed Hawks than typical have been reported in recent weeks, mostly 
concentrated along Lake Michigan and the eastern Soo area. Northern 
Goshawks have been regularly seen, and there have been 3 Red-shouldered 
Hawk sightings in January! Surprising, Rough-legged Hawk sightings are 
average, if not a little low this winter. Multiple species of of 
white-winged and dark-mantled gulls were observed in December, but as 
expected, the number of gulls wintering in the UP drop rapidly in 
January. It has been an excellent season for Northern Hawk Owls with 7 
birds reported this winter so far. Snowy Owl numbers, while not has high 
as last winter are present in decent counts. However, Great Gray Owls 
remain scarce for yet another winter. While the numbers of Black-capped 
Chickadees are very good this winter, numbers of Boreal Chickadees have 
not corresponded. Red-breasted Nuthatches are present in very low 
numbers. Bohemian Waxwing may be the only irruptive passerine
that is regularly being seen this winter with flocks reported across the
peninsula. As expected over-wintering sparrows are rare, though 2 
reports of January Fox Sparrows from Lake Michigan is notable, but 
decent counts of Snow Buntings have been made in the eastern and 
southern UP. Finally there is a real lack of winter finches in the UP 
this season. Pine Grosbeaks are scarce, Purple Finches absent, Pine 
Siskins seen primarily as accessory's to moderate-sized goldfinch flocks 
present, and there have barely been any reports of Redpolls. There have 
been several sightings of Evening Grosbeaks from rural village 
locations- small towns with feeders seem to be the preferred site for 
this species. Red Crossbills have been reported in low numbers north of 
Marquette and in the west unit of the Hiawatha National Forest, and 
there have been a few reports of White-winged Crossbills in the
upper Keweenaw. I have posted photos of the Yellow-billed Loon and one 
of the Audubon's Warblers in the 2009 photo gallery at www.upbirder.org

Highlights

*YELLOW-BILLED LOON*
"AUDUBON'S" YELLOW-RUMPED WARBLER**
Cackling Goose
Ruddy Duck
  Spruce Grouse
Golden Eagle
Iceland Gull
Thayer's Gull
Lesser Black-backed Gull
Snowy Owl
Northern Hawk Owl
Black-backed Woodpecker
Boreal Chickadee
VARIED THRUSH
Bohemian Waxwing
Palm Warbler
ROSE-BREASTED GROSBEAK
unidentified ORIOLE SPECIES
*Exotics*
*Eurasian Siskin*

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