On 4/14/10 I found my first nest of the season, a blue-gray gnatcatcher nest under construction at Spring Grove Cemetery in Cincinnati. The nest is in a shagbark hickory whose DBH measures 108 3/16 " or 9.016 ft at diameter breast height. The nest is situated on a thin branch with a thicker branch shading it just above. The orientation of the nest from the trunk of the tree is 30 degrees NNE. As I did not have my equipment with me when I found the nest, it being the first of the season, I estimated the height to be about 50 ft. To accomplish this, I imagined copies of myself standing upon my shoulders until I was able to reach the nest. Since my height is 5 ft. 11", I rounded my height to 6 ft. for easier calculation and imagined 8 copies of this 6 ft. person to reach the nest. This is 8x6 = 48 ft. I rounded this to 50 ft. Had I used the 5 ft. 11", my estimate would have been 47 1/3 ft.
 
Today, I went back to the nest with my equipment. Using a 100 ft. open reel tape measure, beginning at the base of the nest tree, I measured out 85 ft. of tape and stood at this mark. With a Suunto Optical Reading Clinometer (PM-5), I measured the percent slope from my line of site to the nest and percent slope from my line of site to the base of the tree. I also noted the degree slope of the ground from my position to the base of the tree to be 7 degrees. The percent slope of inclination to the nest was 62%. The percent slope of declination to the base of the tree was 12%. Adding these, we have 72%. Take 72% of the ground distance from the tree, that is, take 72% of 85 ft. This gives 62.9 ft. Multiply this by the cosine of the degree slope (to correct for the ground distance, since it's not on level ground) and we have the height of the nest. So 62.9 x cos 7 = 47.42 ft. As we can now see, my method of estimation was very close to the true height of the
 nest.
In a similar manner, we can determine the height of the tree. With an inclination percentage of 90%, I determined the height of the tree to be about 65.36 ft.

David A. Brinkman
Cincinnati, OH





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