Geography Reference
In-Depth Information
My ancestors crossed the Alps from northern Europe into the lake region
of northern Italy during a warm interglacial period around 1600 BCE. House
sparrows, commensal with humans at that time for about i fty-i ve hundred
years, likely joined the trek. Once across the Alps, house sparrows spread
south and encountered the closely related Spanish sparrow in wilder areas
and especially in wetlands and along stream corridors. Probably because
house sparrows were rare, especially at the fringes of their distribution, they
interbred with the more common Spanish sparrow, creating a hybrid of dis-
tinctive coloration; males had the bright white cheeks and rufous cap of the
Spaniard paired with the clean breast, small black bib, and gray rump of the
northern immigrant. Females of all three varieties are similarly dull and hard
to distinguish.
As human populations in the north increased, so did house sparrow num-
bers. With more pure house sparrow mates available, crossbreeding would
have declined. Hybrids, however, were fertile. So as house sparrows kept to
themselves and stayed mostly around the Alps, hybrids were likely to selec-
tively pair with one another, learning the proper mate by observing the charac-
teristic plumage of their parents. Hybrids may have been especially forced to
mate with their own kind about 350 to 450 years ago when persistent cold
weather closed the passes through the Alps for most of each year and curtailed
the l ow of pure house sparrow genes into Italy. Similarly, the Mediterranean
Sea limited the spread of pure Spanish sparrow genes into Italy from southern
Europe and Africa. Hybrids became increasingly common throughout much
of the Italian peninsula. Today, the Italian sparrow is a recognized species of
hybrid origin that interbreeds rarely with house sparrows in the north and re-
mains genetically pure by a combination of its large population size, preference
for similar-looking mates, and isolated geography. They are the most common
bird species in all of Italy. Some i ve million to ten million pairs live like house
sparrows in all the major Italian cities except those on Sicily, Pantelleria, and
Sardinia, where only Spanish sparrows reside.
