Woodland Creek Soay Rams

Woodland Creek Soay Rams
Soay Sheep Ram Assortment

Wednesday, March 24, 2010

Soay sheep lamb weights and owl lift capabilities

OK, so I'm an an analytical nerd. I did a quick google search on Soay sheep lamb weights and came up with the following article:


Predictors of early survival in Soay sheep: cohort-, maternal- and individual-level variation
Owen R Jones,* Michael J Crawley, Jill G Pilkington, and Josephine M Pemberton, Proc Biol Sci. 2005 December 22; 272(1581): 2619–2625. Copyright © 2005 The Royal Society
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559978/

Their data set was the 1989 to 2002 surveys of Soay sheep on the island of Hirta in the St. Kildas, so it is "real" Soay sheep.

While not explicitly publishing lamb weights, they reported them in their analysis on survival factors. From their Figure 2a, shown here:


I extracted their data from the figure above and calculated a mean value for weights in pounds.
The weighted average lamb weight in the above set was 3.94 pounds. OK, call it 4.
Although the data reported was categorical rather than continuous, so no proper standard deviation can be calculated, from visual inspection above one can deduce that about 90 percent of the lambs were between 1.7 and 5.7 pounds - quite a large range.
So, if, as reported, the Great Horned Owl can lift 5.5 lbs, there is a fair probability that any given lamb would be small enough to be taken.
Sadly, it was noted in the birding sites about Great Horned Owls that, uniquely, frequently take skunks. Now just think of a white-spotted solid black Soay lamb. Looks a lot like a skunk in the early morning light....

7 comments:

Michelle said...

Certainly sounds feasible, and good to know. We have great-horned owls around here, and Shetland lambs can be in that range. I haven't let any of mine lamb in the open, though. I don't have the coyote-proof perimeter fence you have....

Gevan said...

I think I'll call my fence "coyote resistant" rather than "coyote proof". One did sneak under the fence at the creek outlet last year and snagged one ewe...

TyMarrs said...

But could a 5 oz bird carry a 1 lb coconut?

TyMarrs said...

It could grip it by the husk.

Gevan said...

Oh, yeah, an African swallow maybe, but not a European swallow. That's my point.

Sierra said...

Are you suggesting coconuts migrate?

Gevan said...

Oh my children - what have I wrought...