4S DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. 
Much the same, though with certain obvious limitations, may be said 
of the species that are disseminated by the agency of birds. The well- 
known fact that some birds migrate practically the whole length of the 
American continent, from beyond the Arctic Circle to Patagonia and 
return, indicates the possibilities in this direction. 
W. E. D. Scott has named 248 species of birds as occurring within 
the region extending 80 miles north and 40 miles south of Tucson, of 
which, aside from those ranging through the whole region, “common 
on the plains” or “among the giant cacti,’ and therefore to be counted 
in, no less than 69 are specifically mentioned as found in the vicinity 
of Tucson. (See Bailey, 1902.) 
When it is considered that this list includes ducks and other aquatic 
birds, doves, woodpeckers, jays, crows, and many other birds whose 
efficiency as distributors of seeds is well known, it is seen at once that 
the birds which visit Tumamoc Hill and the adjacent valleys are both 
numerous and active enough to count as a factor of prime importance 
as an agency of dissemination. Exact observations of species known 
to be introduced by their means are not easily made, but from what has 
been seen of the feeding on cactus fruits and mistletoe berries by wood- 
peckers, and the extent to which the seeds of various crucifers, plantains, 
and other annuals are eaten by various small birds common about the 
Desert Laboratory, it is perfectly certain that many species of plants 
now growing here are carried year after year, often to long distances, by 
birds, and presumably found their home here originally by the same 
‘agency. According to Tuomey, “nearly a half hundred birds feed upon 
the fruit of the giant cactus, the list including all our thrashers, wood- 
peckers, finches, and pigeons.”’ 
But while birds function most conspicuously as disseminators of seed 
to the advantage of the species thus distributed, their relation to the 
vegetation of Tumamoc Hill is, in some few cases at least, unequivocally 
destructive. Thus the Gila woodpecker, Melanerpes uropygialis, makes 
large holes in the giant cacti by which the natural protection of the soft 
parts within is so far destroyed that decay, often involving the destruc- 
tion of the plant, ensues. 
A considerable number of mammals, conspicuous among which are 
jack-rabbits, squirrels, rats, and gophers, make their home on Tumamoc 
Hill or in its vicinity, and are in close relation to the vegetation either 
as active agents of seed dissemination or as destroyers, some of them 
playing a double réle very effectively. Squirrels here, as elsewhere 
(compare Bailey, 1905), fatten on the fruits of the bisnaga (Echinocactus 
wislizent), and these and other rodents are doubtless responsible to a 
very large extent for the transfer of various edible fruits and seeds to 
limited distances, and very likely assist materially in carrying from one 
point to another seeds that are provided with hooks and similar appen- 
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