Ornithology, Evolution, and Philosophy 123

168 4 Ornithologist and Zoogeographer
and rejoining of populations in the Philippines and Solomon Islands (Delacour
and Mayr 1946k, Mayr and Diamond 2001g: 7–9); tectonic uplift in southern Central
America led to faunal interchange between North and South American faunas
(1946h, 1964c); continental drift caused the separation of North American and
European faunas during the early Tertiary (Mayr 1990b). Until the concept of plate
tectonics was accepted during the 1960s, zoogeographers like Mayr, Darlington,
Simpson and others, did not consider continental drift to explain extant distribution
patterns in birds. This is understandable, because the evolution of most extant
groups of birds and mammals took place during the Tertiary after Gondwana had
split into the series of southern continents.
Speciation models reflecting the processes of jump dispersal and vicariance are
the founder model (peripatric speciation) and the dumbbell model (dichopatric
speciation), respectively. Modern authors occasionally call the leading zoogeographers
of the 1930s to 1950s “dispersalists,” thereby overlooking the fact that their
theoretical framework included various types of vicariance which they proposed
had an effect on faunal differentiation (Table 4.1).
North and South America
Most of the North American families and subfamilies of birds are either Old
Worldinorigin,SouthAmericaninorigin,ormembersofanautochthonous
North American element. This latter endemic element developed during the period
of geographical isolation of North America during the Tertiary, when the
southern half of North America (from about Honduras to the present Canadian
border) had a tropical-subtropical climate. During that time, most of northern
Middle America was a southern peninsula of North America. The tropical North
American element includes the Mimidae, Vireonidae, Parulidae, Troglodytidae,
nine-primaried oscines, and Momotidae. Mayr (1946h, 1964c) identified the following
components (elements) in the North American bird fauna: Unanalyzed
(oceanic, shore and freshwater birds, hawks, eagles, and others), Holarctic (Pan-
Boreal), Pan-American, Pan-Tropical (trogons, barbets, parrots), South American,
North American, Old World (Eurasian). The North American element comprises
up to 50%, or even more, of the North American bird fauna in all habitats except
the arctic. Therefore the North American bird fauna cannot be included in
a “Neotropical” or in a “Holarctic” region. The South American element increases
gradually southward. No boundary line separating North American and South
American bird faunas can be drawn in Panama, because they were mingled in
Pliocene time. Many more Palearctic birds immigrated into North America than
in opposite direction (e.g., the wren colonized Europe). Several North American
groups had secondary radiations in South America (Parulidae, Thraupidae) and in
the Old World (Emberizinae). The suboscines with 10 families are clearly of South
American origin, and only the Tyrannidae and the hummingbirds had secondary
radiations in North America. Faunal interchange between North and South America
occurred mainly toward the end of Tertiary, when the last gap between Panama