NORTHERIvr BLACK SWIFT 265 



He tells me that this swift has a complete molt during summer 

 and is in full fresh plumage before leaving in fall. 



Food. — The northern black swift feeds entirely on the wing, where 

 it is very successful in catching the flying insects, on which it feeds 

 exclusively; it captures a great variety of insects, and anything in 

 the way of aerial insect life seems to be acceptable to it. Mr. Rath- 

 bun (1925) publishes a detailed list of the contents of six stomachs, 

 collected by him near Seattle between June 22 and September 7 and 

 reported on by the Biological Survey. The list is too long to be 

 included here. The stomachs were reported as all full and all 

 containing 100 percent animal matter. Prominent among the con- 

 tents were caddisflies, Mayflies, crane flies and various other flies, a 

 variety of beetles, many termites and flying ants, numerous plant lice, 

 leafhoppers, treehoppers, wasps, and a few moths and spiders. 



Clarence Cottam has sent me the following notes on the contents 

 of 36 stomachs of this swift, as analyzed in the laboratory of the 

 Biological Survey: 



"Both in frequency of occurrence and in total percentages o'f 

 volume, ants, bees, and wasps (Hymenoptera) appear to be the 

 dominant food items taken by the black swift. Ants of the genus 

 Lasius were consumed by 6 of the 36 birds here considered and com- 

 prised 90 to 100 percent of the total content, averaging about 150 

 individuals per stomach. The paper wasps (Vespula) were ingested 

 by one-sixth of the birds and formed 51 to 87 percent of the food. 

 Traces or small percentages of the Ichneimionidae, or parasitic wasps, 

 occurred in the majority of the stomachs. 



"Flies (Diptera) were a close second in importance and formed at 

 least a trace in most of the stomachs ; in many they made up 70 to 95 

 percent of the total content. The principal types met with were the 

 long-legged flies (Dolichipodidae), flesh flies (Sarcophagidae), root 

 maggots (Anthomyiidae), crane flies (Tipulidae), midges (Chirono- 

 midae), Ephydridae, and the grass-stem maggots (Chloropoidae). In 

 a series of six birds from King County, Wash., flies of nine genera 

 made up 100 percent of the contents. 



"Many species of beetles (Coleoptera) were encountered in the food 

 items, but most of them made up only minor percentages or traces, 

 and in only a few cases did they amount to as much as 6 percent of 

 the total. The chief families of Coleoptera taken were the ground 

 beetles (Carabidae), rove beetles (Staphylinidae), weevils (Curcu- 

 lionidae), leaf beetles (Chrysomelidae), click beetles or wireworms 

 (Elateridae), and scarab beetles (Scarabaeidae). 



"Large termites, or white ants {Thermopsis angusticollis) , also 

 known as Isoptera, were the principal items consumed by four of 



