NO. 2298. THE GUANO BIRDS OF PERU—COKER. 473 



eggs are present the parent birds will, after some threatening croaks 

 or whistles, fly when the observer is within a few feet; but they will 

 cover the small young, or stand by the larger nestlings, and often 

 vigorously defend them with their bills. When first examining the 

 nests, it was necessary sometimes to push the bird from the nest to 

 discover the young occupants. Once separated from the nest, the 

 bird gives up the fight and flies away some little distance to remain 

 until the mtruder departs. The gallinazos, however, are usually 

 even more prompt than the parent to find the exposed nest and 

 eagerly devour the eggs or young. On a later page it is told how a 

 gallinazo or a gaviota will provoke a gannet to attack in defense of 

 its home, while other birds will then ravage the nest. As with the 

 other gannets and the pelicans, it is the habit of the nebouxi to dis- 

 gorge the fish from its crop before startmg in flight, presumably by 

 way of "throwing over ballast" to facilitate escape. 



There are very evident sex distinctions. In every pair, one has 

 a large black pupil and narrow yellow iris and quawks vociferously 

 when an intruder approaches the nest; the other has a smaU pupil 

 and broad iris, manifests a darker ground color of head, and utters 

 only a hoarse whistle v/hen approached. The supposition that this 

 distinction corresponds to sex was not verified at the tune by kiUing 

 the birds for examination of the gonads, but I find that, of the pair 

 which I killed and sexed on another occasion, it is the male which 

 displays the darker ground color on the head, with more sharply 

 contrasting white streaks, and the same is true of other specimens in 

 the United States National Museum. Of 23 nests in which the parent 

 birds were carefully noted, 11 were covered or guarded by the male 

 (whisthng parent with darker head, etc.), 8 by the female (quawking 

 parent), and 4 by both. The immature but grown young are much 

 darker than the mature males or females especially as to the head, 

 and they show no yeUow in iris. All the young seem to make the 

 quawking sound. 



The season of breeding seems to be uninterrupted. When the 

 Lobos de Ticrra Islands were first visited, March 29 to April 6, 1907, 

 nests with eggs, with newly hatched young, or with feathering birds, 

 were found in nearly equal proportions; and this was also the case 

 at the second visit in early December of the same year. 



In spite of its habit of nesting upon the level and accessible places, 

 this species does not seem to be of high relative importance for its 

 guano production. Its guano is so widely scattered over the ground 

 as not to be readfly appreciable in a season, but undoubtedly, in the 

 long run, the production of guano is of distinct value. 



