ANNA'S HUMMINGBIRD 385 



sufficient to distinguish it from Anna's at any time. Both sexes of 

 Anna's can be separated from the rufous, Allen's, and broad-tailed 

 hummingbirds by the entire absence of rufous or brownish coloring 

 in the plumage. The male differs from the black-chinned and Costa's 

 in the color of its throat and crown and in the fact that the gorget is 

 bordered below by gray, instead of white. The adult female usually 

 has a central patch or scattered spots of luminous red on the throat; 

 otherwise it can generally be distinguished from Costa's by its larger 

 size and darker underparts, and from the black-chinned by its stouter 

 form. In size and general appearance, including the color of the 

 throat, Anna's is probably most like the broad-tailed, but the normal 

 ranges of the two species are entirely separate. 



Enemies. — The hummingbird is one of the most notable exceptions 

 to the rule that smaller animals must be more prolific than larger ones 

 in order to compensate for an inherently higher mortality rate. Nev- 

 ertheless, the eggs and young of hummingbirds seem to be subject to 

 more than ordinary vicissitudes. The small size and fragility of the 

 nest, together with its usually exposed situation, make it liable to 

 destruction by storms or accidents, w^hile the long period between the 

 laying of the eggs and the fledging of the young increases the pos- 

 sibility of loss. The eggs are said to be often taken by the California 

 jay {Aphelocoma calif ornica)^ and quite possibly they may be eaten 

 by the banded racer {Bascanion later ale) and the alligator lizard 

 {Gerrhonotus scincicauda), as these reptiles are frequently seen 

 climbing through the foliage of shrubs and trees. In some cases, 

 also, one of the eggs will fail to hatch, even though not disturbed. 

 In their earlier stages, the young are probably threatened by the 

 same enemies previously mentioned, while the spotted skunk {Spilo- 

 gale phenax) is always a definite peril if the nest is within its reach. 

 Another source of danger to the young birds is mentioned by Mr. 

 Anthony (1923) : 



The ornithologist visiting San Diego is usually impressed with the surprising 

 scarcity of nesting birds in Balboa Park, though the surroundings seem to be 

 ideal. It was not until I had been at the San Diego Museum of Natural History 

 a year, that the possible explanation was presented. A swarm of bees that bad 

 been installed as an exhibit in the museum was destroyed in a few days by an 

 insignificant ant. This ant, I was told, had in all probability reached our 

 shores with some of the trees or shrubs brought in from South America. It 

 was known as the Argentine Ant. * * * 



If bees were killed by ants, why not young birds? Several nests of the Anna 

 Hummingbird {Calypte anna) were located and kept under observation and in 

 every case the young were killed and eaten within two or three days of the 

 time they hatched. 



Dependence upon one parent alone w^ould also theoretically increase 

 the chances of failure. All in all, it would seem that the number of 

 young fledged could not represent a very large proportion of the eggs 



178223—40 31 



