Bird watching has been popular for a long time. It goes back at least as far as the 1780 bird-listing song so popular with carolers, The Twelve Days of Christmas. Certainly only birders would count 7 swans (a-swimming), 6 geese (a-laying), 5 golden rings (evidence of historic bird-banding practices), 4 colly birds (blackbirds), 3 French hens, 2 turtle doves, and 1 partridge (in a pear tree).
Even further back, roughly in the year 0AD, odds are pretty good that at least one of the three wise men in the manger was a birder. It was exactly 1,900 years later in the United States when Frank Chapman turned a traditional Christmas Side Hunt into an event for counting birds and pooling their numbers instead of their carcasses. In so doing, he cultivated Christmas spirit towards sharing knowledge instead of consuming resources. Even more, he anticipated that the shared knowledge would be put to use towards conserving our feathery companions. The Christmas Bird Count, now run by the Audubon Society, is an iconic example of citizen science. To this day, many say “bah-humbug” to their holiday shopping list in order to make time for their species checklist.
And for many bird lovers, one annual tradition is not enough. People extend the Christmas spirit of the Audubon event by sharing their observations in other programs. These include Project FeederWatch (November through early April) run by the Cornell Lab of Ornithology and Bird Studies Canada, and the Breeding Bird Survey (summer) run by the US Geological Service’s Patuxent Wildlife Research Center and the Canadian Wildlife Service.
Several years ago, I realized that data from the Christmas Bird Count might shed light on a fundamental issue in ecology: competition between species in the wild. With enthusiastic colleagues, we analyzed trends of two very common species in Christmas Bird Counts for a research paper in the journal Ecology.
The hypothesized competitors were House Sparrows and House Finches. If you watch a bird feeder, you may even see these two common birds interact in ways that generated this initial hypothesis of competition. These two species fight for the same food.
House Finches are small, brown streaked birds, and the males, when on the right diet, have lipstick red feathers on their heads and upper bodies. They are native to the western US and were introduced to the eastern US in the 1940s. House Sparrows are native to Europe and only introduced to the US in the late 1800s. You are probably familiar with them as they hop around to eat crumbs in parking lots or under tables at any outdoor café. These are rough-and-tumble little birds that don’t just challenge birds their own size: they also can out-compete their much larger cousin, the Eastern Bluebird, in battles over nestboxes.
We confined the study to the Midwestern US, where neither House Finches nor House Sparrows were in their native range, neither holding a home-field advantage.
For ecologists, seeing two species fight doesn’t qualify as sufficient evidence for competition; we need to see a population-level response. In captivity, researchers can see when two species of fruit flies cannot coexist, but how relevant is that to how competition influences wild populations? In field studies, when similar species are able to co-exist, the differences in their niches are often interpreted as evidence of past competition. Ongoing competition is hard to show in the wild because it requires experimentally altering one population and looking for a response in the other and then vice versa to validate. Thus, only through field experiments that manipulate populations can we find reliable evidence of competition. After the introduction of House Finches to the eastern US, researchers began to make a case for competition by noting subsequent declines in House Sparrows. But the vice versa was needed to confirm.
Opportunity for this confirmation presented itself when House Finches declined dramatically in 1994-96 in the mid-western US due to the spread of a conjunctivitis eye disease. The spread of the disease was tracked through citizen science efforts in the House Finch Disease Survey, and continues to be tracked directly through Project FeederWatch. The rise and fall of House Finch populations from invasion and then disease, in areas with House Sparrows, created a natural experimental test of competition. There are few opportunities to look for evidence of competition among wild birds, especially at such large scales. We couldn’t have taken advantage of this opportunity without citizen science.
The long-term monitoring in the Christmas Bird Count revealed the vice versa: House Sparrows increased soon after House Finch declined from disease. And we found the same support from observations contributed to Project FeederWatch and the Breeding Bird Survey. This means that House Finches are the competitive winners, giving House Sparrows their come-uppance, except when other factors, like eye disease, turn the tables and decrease the House Finch populations.
Science is based on observation, as is bird watching. No wonder science and birding have been united by citizen science for over a century. Over 70,000 people participated in the Christmas Bird Count last year. I’m sure there will be even more this year. Let’s celebrate the holiday season with good will towards all birds.