[TN-Bird] Loons Species Size Differences

From: OLCOOT1@xxxxxxx
To: tn-bird@xxxxxxxxxxxxxx, albirds@xxxxxxxxxxx,ARBIRD-L@xxxxxxxxxxxxxxxxx, HapC1@xxxxxxx, roseanna@xxxxxxxxxxx,dlroemer@xxxxxxxxx
Date: Tue, 9 Mar 2004 18:57:39 EST
Chatters,
There has been some discussion as to the size differences of the various 
loons that are present at this time at Pace point. I thought the following 
statistics might be interesting.

I gleaned most of this from a couple of books some time back when I was 
interested in the size differences I was seeing in Common Loons while looking 
for 
Pacific Loons. It seems a lot of small Common can be as small or even smaller 
than a Pacific Loon, so a very small loon needs to be checked out for other 
indications of species before jumping to Pacific due only to size. 

The average sizes by weight listed for the species in Sibley's (the best part 
of his book is that he gives weights!) is really great, from 3.1 pounds for 
the Red-throated, to 3.7 pounds for the Pacific, to 9 pounds for the Common, 
and then 11.8 pounds for the Yellow-billed. 

I had often run across variances in Common Loons in the field time and time 
again and 
found that they vary really big time according to literature with some male 
Commons almost triple the weight of the smallest female. Male Common Loons 
average 30% larger by weight than female and even overlap some small female 
Yellow-billed Loons, although the avg. YBLO female is larger than the avg. male 
Common Loon by about 35%.

There is no doubt that our immature Yellow-billed at Pace is large and does 
overpower the Common Loons it is with but you should have seen the 2nd winter 
bird, it appeared at all times much larger than any of the many Commons it was 
seen with. Everyone that has seen the two birds agree that the first bird was 
huge. Even those that had seen the bird in Georgia said our bird appeared much 
larger. The YBLO evidently takes at least 2 years to mature and that may 
explain a lot of the apparent size differences.

I pulled out some old figures that I looked up some while back on Common 
Loons and found some interesting results. Large male Common Loons can be 77% 
larger than the smallest males and large females can be almost 4 TIMES larger 
than 
the smallest adult females by weight, but the difference between the avg. 
sexes has the male only 30% larger than the avg. female but that is still a big 
difference.

In Yellow-billed Loons the largest males are 80% larger than the smallest 
males with the large females larger than the smallest males by up to almost 10% 
and these females are 57% larger than the smallest females. The avg. male 
Yellow-billed is only 5% larger than the avg. female.

If you have the smallest female Common Loon next to the largest male 
Yellow-billed Loon, he could be an amazing 4-1/2 times as large by weight!!!!!!!


Good Birding!!!

Jeff R. Wilson
OL'COOT / TLBA
Bartlett, TN


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[TN-Bird] Loons Species Size Differences

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