In the last column, we explored the biology of House Sparrows. This species is dependent on human-altered landscapes for their existence. The abundance of House Sparrows and their tolerance of human proximity make House Sparrows excellent subjects for ornithological research. In today’s column, I will review some of the research on these birds.
House Sparrows can change habitat preferences quickly. Introduced into eastern North American 1n 1851, House Sparrows were most common in cities. Until the turn of the 20th century, urban areas where perfect for House Sparrows. Horses provided the major means of human transportation and the hay to feed to horses had plenty of seeds to satisfy the cravings of House Sparrows. Many seeds pass through a horse gut intact so horse droppings provided good foraging as well.
As automobiles replaced horses in cities, House Sparrow abundance in cities declined and the birds shifted their preference for agricultural landscapes. The primary food of most House Sparrows is now cereal grains like wheat, corn and oats. Some Argentinian House Sparrows make ends meet in urban environments by feeding on the nectar produced by aloe plants in public parks.
House Sparrows have provided a test of Bergmann’s Rule. This rule states that the size of members of a species (or related species) should increase as one goes from the equator to the poles.
The reason is related to the challenges of maintaining a constant body temperature at colder temperatures. A larger animal has a lower surface to volume ratio. Heat is lost across the surface of an animal but produced by all the cells in the body, hence proportional to volume. In seasonal environments where food abundance is highly variable, a larger animal will be able to tolerate lack of food longer than a smaller animal.
Studies of the geographic variation in size of House Sparrows in North America provide support for Bergmann’s Rule. From an initial introduction, House Sparrows have spread broadly throughout North America. Size is negatively correlated with average January temperatures and size is positive correlated with latitude. In Europe, the pattern is murky. No strong pattern of increase in size occurs with increasing latitude. More work is needed.
Male House Sparrows have a black bib. Animal behaviorists call such a feature a badge. The extent of the black is an advertisement for the quality of the male; females choose a mate, at least in part, based on the size of his badge.
We know that males with larger birds acquire a mate earlier than small-badged males. Large-badged birds also usually have superior nesting territories.
We think of House Sparrows as monogamous birds. From DNA fingerprinting, we know that cheating on a spouse is common in House Sparrow communities. About 20% of nestlings are sired by a male other than the female’s mate.
Research in Sweden indicates that large-badged males are received more frequently in extra-pair dalliances than small-badged males. The tables can be turned. The mate of a large-badged male is often cheated on by his mate.
Some House Sparrows in New Zealand are clever birds indeed. In Hamilton, House Sparrows fly into the bus station when the automatic glass doors slide open, activated by an electric eye. The House Sparrows find plenty of food to eat from the crumbs that humans drop from their breakfasts and lunches purchased inside. The Hamiltonians are very tolerant of the scavenging House Sparrows.
A hungry House Sparrow needs to wait for a human to enter or exit the bus station so the doors slide open. However, some House Sparrows have figured out they can perch on top of the small metal box above the door that houses the electric eye. The birds lower their head to break the laser beam and, voila, the door opens when the sparrows want to get in.