I24 Thayer on Protective Coloration. L April 



1889, I found a nest in a small oak, containing two eggs. May 4, 1894, 

 I found a pair brooding. May 16, a pair were building in an oak, fifteen 

 to twenty feet above the ground. May 2S, the birds seemed to be through 

 building and were flitting about warbling and apparently taking a rest 

 before time to begin brooding. May 31, after a Blue Jay had created an 

 excitement in the oak, the Gnatcatchers began taking their nest to pieces, 

 and went to work putting it up in a low oak a few rods away. June 7 the 

 birds were still building. June 11 they were brooding, changing places 

 in the nest. June 25 the young were being fed. July 4 the young were 

 out. being fed in the brush. From May 16, or more accurately May 14 — ■ 

 for the nest had been begun at least two days before I found it — from 

 May 14 to July 4, those birds were working to get one brood launched. 

 The first nest took them two weeks, the second one about ten days. Their 

 method of work was interesting. The nest was laid on a horizontal 

 branch. Their plan seemed to be twofold, to make the walls compact and 

 strong by using only fine bits of material and packing them tightly 

 together — drilling them in — -and at the same time to give the walls form 

 and keep them trim and shipshape by moulding inside and smoothing 

 the rim and the outside. Sometimes the builder would smooth the brim 

 with its neck and bill like a Redstart, as a person sharpens a knife on a 

 whetstone, a stroke one way and then a stroke the other. The birds 

 usually got inside to work, but there was a twig beside the nest that 

 served for scaffolding, and they sometimes stood on that to work on the 

 outside. They both worked, flying rapidly back and forth with material. 

 The second nest rested lightly on a horizontal limb, but was supported 

 mainly by two twigs which forked so as to enclose it. It was a beautiful 

 nest, covered with lichen and lined with feathers. The birds were not 

 at all shv. They let me come so near that 1 saw the black lines bordering 

 the blue forehead of the male. 



Sialia mexicana occidentalis. Western Bluebird. — Mr. Merriam 

 told me he had seen the Bluebirds build in the mud nests of Swallows in 

 trees; but most frequently in knot holes and in the abandoned nests of 

 the small Woodpeckers. 



THE LAW WHICH UNDERLIES PROTECTIVE 

 COLORATION. 



BY ABBOTT H. THAYER. 



This article is intended to set forth a beautiful law of nature 

 which, so far as I can discover, has never been pointed out in 

 print. It is the law of gradation in the coloring of animals, and 



