House sparrows (Passer domesticus) are one of the most familiar birds in the world, easily recognized by even novice birders. How much do you really know about house sparrow history, however, and how did these little brown jobs become the most abundant songbird in the world?
House Sparrow Origins
The house sparrow is an Old World sparrow believed to have evolved in the Mediterranean region centuries ago. As human civilizations spread across Europe, so did these little birds, and they are rarely found away from human habitation. All modern house sparrows are descendents from that original European or English sparrow, but today they have spread around the world.
House Sparrows in the New World
House sparrows were first introduced to North America when a few dozen birds were released in Brooklyn, New York, in the fall of 1851 and spring of 1852. Gradually the population grew and was augmented by additional releases because settlers then believed that these birds would help control insects on crops. House sparrows were released in many places in the New World in the next few decades, including…
- Portland, Maine: 1854-1858
- Hawaii: 1871
- San Francisco, California: 1871-1872
- Brazil: 1872
- Salt Lake City, Utah: 1873-1874
- Bahamas: 1875
Unfortunately, it wasn’t realized initially house sparrows only eat insects when their nestlings are very young, and during the rest of the year the birds fed on the very grain crops they had been imported to protect.
How House Sparrows Spread
House sparrows are hardy, adaptable birds that were able to spread very quickly from their introduction points. Several factors allowed the birds to spread phenomenally fast:
- Early Breeding: House sparrows begin their nesting season as early as late February, allowing them to claim prime nesting spots before native birds arrive during spring migration.
- Multiple Broods: A mated house sparrow pair may raise up to four broods of nestlings annually. Each brood typically contains 4-7 eggs, causing exponential population growth from even just a few initial birds.
- Few Predators: Because house sparrows are most comfortable around human habitation, there are fewer nearby predators that can keep the bird population manageable. Furthermore, many hunters were killing the very birds of prey that might have helped control house sparrows when they were first introduced.
- Varied Diet: House sparrows eat a wide variety of items, including seeds, insects and grains. The spread of agriculture helped encourage the birds’ population growth since there was more grain for food and horse-drawn transportation in urban areas ensured spilled grain from feedbags and grain in horse feces for the birds to feed on.
- Year-Round Range: House sparrows do not migrate, which allows them to stay in the same breeding ranges when other birds relocate to warmer winter climates. This is another way house sparrows are able to breed earlier than many other bird species.
- Varied Nests: House sparrows aren’t picky about where they build nests, which gives them many more potential nesting sites to use. Furthermore, they may reuse nests for different broods and in consecutive years, further shortening the time between each clutch of eggs and allowing faster population growth.
Changes in House Sparrows
Because house sparrows are widespread and abundant, and because they have little fear of humans, they are perfect for ecological studies. To date, there have been more than 5,000 studies using house sparrows as subjects, and a great deal is known about these birds.
For example, it has been discovered that not all house sparrows are the same. European house sparrow populations contain 11 distinct subspecies that have discernable variations in size, with smaller birds with shorter legs and wings found in cooler climates and larger birds better adapted to warmer climates have better heat dispersal through longer limbs. This is proof of these birds’ adaptability and evolutionary success, and that is part of what makes them such a widespread species.
House Sparrow Threats
Today, house sparrows are seen as pests and invasive birds in many regions, with good cause. They can crowd out native birds, disrupt food supplies, damage crops and transmit diseases. As early as 1883, conservationists were urging people to eradicate house sparrow populations through trapping and killing the birds, and bounties were offered on dead house sparrows. While cookbooks no longer print sparrow recipes and contests aren’t held to reward winners with the most carcasses, lack of protection for these birds in many areas is having an effect.
Because of concerted efforts to control house sparrow populations, the overall numbers of these birds are now declining around the world. Threats to house sparrows include:
- Efficient agriculture with less wasted or spilled grain
- Pesticide use that eliminates insects as a food source
- Individual efforts to discourage house sparrows from feeding or nesting
- Feral cat populations that prey on these ground feeding birds
Can these threats, along with dedicated efforts to reduce house sparrow populations, completely eliminate the birds from large regions? While such consequences are theoretically possible, it is unlikely because the extreme measures necessary to do so would likely have adverse effects on other bird species long before house sparrows disappeared.
The Future of House Sparrows
Today, the house sparrow is the world’s most abundant songbird and it can be found on every continent except Antarctica. Despite that abundance, however, dislike of the house sparrow’s aggression toward native species has made it one of the world’s least popular species, and the birds face many threats. While there are still hundreds of millions of house sparrows successfully foraging in cities and towns around the world, it is possible, if unlikely, that one day these little brown birds may become threatened or endangered. By understanding the house sparrow’s long and adaptive history, birders can better appreciate the hardiness of this species and work to manage its population without eradicating it entirely from areas where it is one of the most familiar birds.
Photo – Male House Sparrow © Keith