64 U.S. NATIONAL MUSEUM BULLETIN 22 3 



niche may be inhabited by more than one species concurrently. It 

 seems, in the absence of definite interspecific competition, that the 

 number of similar species temporarily coexistent in a given niche is 

 not subject to a predictable limit, and also that mixing of organisms 

 between niches increases the frequency and the complexity of such 

 natural coexistence. 



Perhaps even more pertinent as comparable material, because of 

 its avian natm-e, is the case of the two species of Sturnella that Lanyon 

 (1957) recently studied. The two are very similar morphologically 

 and in their breeding behavior, but where they overlap, they seem, 

 nevertheless, to be effectively isolated reproductively. The slight, 

 differential ecological preference shown by them hardly constitutes 

 more than a partial isolating mechanism, but, similar to the combas- 

 sous, what else serves to keep them apart is unknown. Lack (1947) 

 discussed a fanly comparable situation in the finches of the genus 

 Geospiza in the Galapagos Islands. 



In most of Kenya and Uganda, areas from which observational 

 data can be expected, only the black-wiuged combassou occurs, but 

 in large areas of Africa the situation is otherwise, and it is hoped that, 

 in them, observers will determine the degree and the manner of 

 coexistence of these closely aUied species. Coexistence raises the 

 question of the applicability of Gause's principle (see Gause, 1934; 

 Crombie, 1947; and Mayr, 1947), which states that generally two or 

 more closely similar species with similar ecological requirements 

 cannot live sympatricaUy indefinitely because one of them will 

 probably prove to be more efficient and will eventually outbreed and 

 replace or supplant its competitors. 



AvicuLTURAL DATA ON LIFE HISTORY: If OUT knowledge of the life 

 histories of the various combassous were greater, we possibly would 

 sense differences in habits and behavior of species that are not now 

 noticeable. Unfortunately, so little is known of any of the species 

 that the full value of some of the published observations cannot 

 be elicited because they cannot be identified to species with certainty. 

 As all the included forms probably differ only in relatively minor 

 ways, however, a few notes not definitely referrable to particular 

 species are worth recording here as contributing to the general pic- 

 ture of the biology of the combassous. 



At this point it is necessary to anticipate the largely unwarranted, 

 but recurrent objections that many field naturalists raise against 

 observations of birds living under the limiting conditions of captivity. 

 Undeniably, the observer must be very much on guard against easy 

 acceptance and uncritical transference of such data into the more 

 arduously pieced-together fabric of the ethology of each species, but 

 the restrictions of captivity enable us to make observations that 



