28 U.S. NATIONAL MUSEUM BULLETIN 265 



evidence that the more meridional breeders are ecologically or geo- 

 graphically separated from the more northern ones, it is not possible 

 to assume that they are isolated into nonintercommimicating gene 

 pools. Because of this it becomes necessary to describe migratory 

 behavior in these species as partial. As pointed out in my earlier 

 study of a very similar situation in the crested cuckoos of the genus 

 Clamator (Friedmann, 1964, p. 76), partial migration is a term used 

 originally for European and North American species in which some 

 individuals are regidarly migratory while others, breeding in the same 

 area, are nonmigratory, resident birds. Strangely enough, the tendency 

 toward migratoriness is not necessarily constant throughout successive 

 years of the life of an individual bird, and apparently it is not necessar- 

 ily an inherited character. This opens the way for a species to increase 

 its range by the migratoriness of some of its members, who the follow- 

 ing season or in the following generations become sedentary in their 

 recently established areas of occupancy. 



The above considerations lead directly to, and help to elucidate, 

 the situation as we find it in the first species to be examined, C. 

 malayanus. This cuckoo, mth 11 subspecies, ranges from the Malay 

 peninsula, from Patani southward, Sumatra, and the Philippines 

 (Negros, Mindanao, Basilan, Tawi Tawi, Bongao), Java, Borneo, 

 Celebes, the Lesser Sunda Islands, Babar Island, Biak, the western 

 Papuan Islands (Weigeu, Misol), New Guinea, the Aru Islands, 

 Vulcan, Dampier, and Fergusson Island, to the Moluccas (Hal- 

 maharea, Ternate, Buru, Ceram, Goram, Amboina), the Tenunber and 

 Kei Islands, to northern Australia (Cape York peninsula, Arnhem 

 Land, the Kimberly district of northwestern Australia, and northern 

 Queensland) . In most of that range it is, so far as known, nonmigratory, 

 but there is some reason for thinking that one population, the race 

 minutillus (northwestern Australia, Arnhem Land, and northern 

 Queensland) may be partly migratory. Mayr (1939, pp. 128-129) and 

 Deignan and Amos (1950, pp. 167-168) have shown that specimens 

 obviously referrable to minutillus have been taken on the islands of the 

 Lesser Sunda and the Molucca group (where there are resident races), 

 riifomerus in the Lesser Sundas, and crassirostris in the Moluccas. 

 It is known that minutillus is present throughout the year in its 

 known breeding area of northern Australia, where specimens have 

 been taken in all months of the year except August and September, 

 and there is no reason for doubting that, if search were made, they 

 would be found in those two months also. The existence of minutillus 

 specimens from the Lesser Sunda Islands, taken in February, April, 

 May, August, September, October, November, and December, raises 

 a question as to what evidence there really is for migTatory behavior in 

 this race. It cannot be resident in these islands sympatrically with 

 rujomerus, or in the Moluccas along side of crassirostris, and still be 



