350 BULLETIN 19 6, UNITED STATES NATIONAL MUSEUM 



re-using the materials to build a new nest a short distance away. 

 L. L. Hargrave (1933) has collected and summarized a number of 

 published accounts of this peculiarity, and he concludes that nests are 

 abandoned because of a change of conditions that renders the first 

 site untenable or at least no longer desirable. He cites one case where 

 a pair of green herons started their nest close to a still unfinished 

 gnatcatcher's nest, and other cases where human interference was 

 probably the determining factor in causing abandonment. A nest, 

 once abandoned, immediately becomes the most convenient source of 

 material for another structure. This use of an existing nest is all the 

 more readily understandable when the extremely seasonal nature of 

 desirable nesting material is considered. In the nest that I described 

 earlier in this section, the predominating materials — oak catkins and 

 "wool" from the cinnamon fern — are obtainable in quantity only over 

 a short period. After this critical period, existing nests are the sole 

 source of supply. Besides the nests that are moved by their con- 

 structors in extension of the original building program, I have known 

 nests in which broods had been successfully reared to be torn up and 

 carried off by gnatcatchers, but whether the "wrecking crew" and 

 the original owners were the same or not, I am unable to state. 



Nest-building in many parts of the gnatcatcher's range precedes 

 egg-laying by 10 days or two weeks. C. K. Lloyd (1932) attempted 

 to account for the need of this interval in the more northern sections 

 by stating that the birds "nest early * * * and do not deposit 

 eggs until the trees are well leafed out," but he gave no reason for 

 the practice of "nesting early." In northern Florida, where many 

 nests are built in evergreen trees and where most of the deciduous 

 trees are in full leaf at the time of nest-building, this explanation 

 does not hold good, yet the same length of time elapses between the 

 completion of the nest and the laying of the first egg as in the North. 

 It seems to me that nest-building is best accomplished at the time 

 that the favored nesting material is obtainable in greatest abundance, 

 even though that does not coincide with egg-laying time. Thus, in 

 northern Florida, nest-building takes place early in April when oak 

 catkins and fern "wool" are available with the least labor of search, 

 but eggs are seldom laid before the third week of April. 



Eggs. — [Author's note: Four or five tiny eggs usually constitute 

 the set for the blue-gray gnatcatcher, seldom more or fewer. They 

 are ovate or short-ovate and have little or no gloss. The ground color 

 is pale blue or bluish white. They are rather sparingly and more or 

 less evenly covered with small spots or fine dots of reddish brown, or 

 darker browns; rarely there are a few very small blotches; sometimes 

 the markings are concentrated in a ring around the large end; and 

 very rarely an egg is almost immaculate. The measurements of 50 



