montane forests, their distribution pat- 
tern may represent an earlier stage 
in the origin of ground tyrants. When 
it inhabited montane forests, the 
proto -Muscisaxicola of the high An- 
des might have looked and behaved 
like a chat tyrant, and then become 
modified during further evolution in 
the treeless puna and paramos. Even- 
tually only the high-altitude species 
survived. 
Figuring out what direction the shift 
in habitat preference took, however, 
is not as straightforward as it might 
seem. At face value, if there are cur- 
rently more species in one habitat 
( puna or paramo) than the other (mon- 
tane forest), the shift would appear 
to be from puna or paramo to forest. 
But speciation and extinction cycles. 
mediated by the external environment 
and modified by competition, could 
have turned things around so that to- 
day’s lowland, forest-dwelling little 
ground tyrant could be either an eco- 
logical relict of the early forest history 
of the genus or a recent colonist from 
high-altitude, open habitats. Because 
it is almost as highly modified mor- 
phologically as the ground tyrants of 
high altitudes (or high latitudes, in 
Patagonia), I propose that the little 
ground tyrant is more likely to be a 
recent colonist. 
This rough sketch gives an idea of 
the many different ways in which the 
birds of the high Andes may have 
evolved. Some species originated right 
there from ancestors that lived in more 
forested environments when the moun- 
taintops were not so high; some are 
relative newcomers whose ancestors 
came from North America, from 
southern South America, or from the 
dry lowlands at the base of the Andes. 
Complicating the picture, some spe- 
cies are little different in morphology 
and behavior from closely related 
birds found elsewhere, while others 
have had a longer, more complex his- 
tory. Challenged to reconstruct this 
history from often woefully inad- 
equate evidence — involving shifts in 
habitat preference that trail far back 
in time, speciation between isolated 
mountaintops, and morphological and 
behavioral adaptations to the high An- 
des — the biogeographer may occasion- 
ally have cause to envy detective Her- 
cule Poirot. □ 
