ing, often come out on the birdhouse 
porches. Since in many martin houses 
all rooms on a tier are connected by 
the same porch, the young may mix 
extensively and move between nearby 
compartments. Older nestlings cause 
much disturbance among the birds 
nesting on a tier, and when they try 
to enter nests containing eggs, they 
are often knocked off the porches by 
the occupants of these nests. These 
older nestlings sometimes successfully 
intrude into neighboring nests and 
usurp most of the food brought by 
parents of the younger nestlings. On 
one occasion, one of us observed a 
nearly grown nestling from one nest 
enter an adjacent room in which the 
young had just hatched. The pair in 
that room promptly abandoned their 
newly hatched young, which later 
died, and fed the intruder, which rap- 
idly gained weight and remained in 
the nest for four days until it fledged. 
Young birds from adjacent-nesting 
pairs are most frequently involved in 
these disruptions, but all pairs that 
use rooms opening on a common porch 
are affected. 
Besides providing nesting sites, peo- 
ple have also provided martins with 
some exotic nesting-site competitors. 
House sparrows and starlings were un- 
wisely introduced into North America 
and have spread phenomenally from 
coast to coast. Both species use holes 
for nesting sites and appear to relish 
martin houses. Rarely is a martin 
house not also occupied by house spar- 
rows, and starlings are a problem in 
some areas. These species fill martin- 
house rooms with bulky straw nests 
and sometimes actively chase purple 
martins away. Bluebirds and wrens 
also often usurp birdhouses erected 
for purple martins. Some people assist 
martins by destroying sparrow and 
starling nests as they are built, and 
others resort to shooting or trapping 
these interloping species. 
The purple martin, regarded by 
some as the premier backyard dweller 
in North America, actually has been 
nesting in large colonies only a short 
time. People have provided martins 
with an abundance of new nesting 
sites; they have also provided pest spe- 
cies that compete for those nesting 
sites. The purple martin thus presents 
an opportunity for evolutionary study: 
over time, we can observe whether 
these birds adapt further to a colonial 
life style. □ 
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