It's winter in North America, but you wouldn't know it in Southern California. In many Los Angeles backyards, Allen's hummingbirds bask in the sunshine as they prepare their nests. To the north, in Seattle, backyards are blanketed in a layer of fluffy white snow. The trees have shed their leaves. Most of the birds that call this city home are hunkering down, waiting for springtime warmth.
This meteorological mismatch means that birds in Southern California are ready to reproduce many weeks before their counterparts in cooler climes even begin to scope out the avian dating scene. A new study suggests that this discrepancy could explain why some conservation groups report massive population declines while backyard birdwatchers record those very same species showing up in record numbers.
A recent report produced by a conservation organization called Partners in Flight lists the Allen's hummingbird as a species of conservation concern. It indicates that the species is suffering especially from restrictions in both its breeding and wintering ranges and has undergone a population reduction of 83 percent. Determining which species are in need of protection is not a trivial matter. Given limited resources, not every species will be able to reap the rewards of human assistance, so some method of conservation triage is necessary. Indeed, federal agencies like the U.S. Fish and Wildlife Service rely on reports like these for determining which species recovery efforts to focus on.
UC Riverside ornithologist Chris Clark thinks that the Allen's hummingbird is not in need of protection. Quite the opposite, in fact. "I had told [Partners in Flight], behind the scenes a couple years ago, that this made no sense at all. Their population model was obviously wrong, it made no sense," he says.
Clark should know. He's been studying hummingbirds for fifteen years, the last four in Southern California. "When I arrived here, I was blown away by how many Allen's hummingbirds there are here. Every ornithologist in Southern California knows the story: Allen's hummingbirds used to not be found on the mainland in Southern California at all, and in the last fifteen years or so they started appearing everywhere." But when he voiced his concerns, he was told that his observations couldn't be confirmed by any peer-reviewed scientific papers. So he wrote one. Originally drafted in just five days, Clark's argument was published last week in the peer-reviewed journal The Condor.
To understand what's going on here requires a bit of ornithological explanation. There are two types of Allen's hummingbird. The migratory sub-species breeds along the California coast from near the Oregon border to Santa Barbara. The sedentary sub-species was once limited to the Channel Islands, and at that time represented perhaps four percent of the entire species. But in the 1960s, they began populating the mainland near Rancho Palos Verdes. And while the migratory birds in the north stick to relatively undisturbed, natural landscapes, the sedentary ones down south have made themselves at home in urban areas.
This explains part of the problem. Formal breeding bird surveys and Christmas bird counts, from which groups like Partners in Flight derive their population estimates, stick to natural habitats, all but ignoring urban backyards and parks. "So the surveys are not measuring where the birds actually are, at least here in Southern California," says Clark.
Then there's the timing mismatch. Most birds in North America breed in June, so that's when the annual breeding bird surveys are conducted. Birds are easier to observe during breeding season, when they tend to stick to one territory and belt out their songs. But because birds in Southern California breed so much earlier, they're a lot quieter and harder to spot by the time June rolls around. According to Clark, "they would find more birds if they looked earlier."
Together, the habitat mismatch and the timing mismatch suggest that the standardized surveys aren't optimized for Southern California birds, making conclusions drawn from them misleading. But it's one thing to say that the breeding bird surveys are suboptimal; it's another to say that the species in question is actually thriving. For that, Clark turned to eBird.
A citizen science initiative based at the Cornell Lab of Ornithology, eBird allows avian enthusiasts to record their bird watching observations throughout the year, and from any location, including backyards and urban parks. While it doesn't have the rigors of a more standardized survey, it offers a far wider perspective on avian biodiversity.
The data confirmed what Clark knew to be true: Allen's hummingbird observations increased dramatically in Southern California starting in the early 1970s, following the sedentary sub-species' incursion onto the mainland. From their initial introduction on the Palos Verdes Peninsula, they have since expanded. Today, they range from Santa Barbara to San Diego and as far east as Riverside. Kimball Garrett, ornithology collections manager at the Natural History Museum of Los Angeles agrees. "I think he's right on. Most birdwatchers in this area have seen the absolute explosion of Allen's hummingbirds."
Using some back-of-the-envelope mathematics, Clark points out that this represents a range of around 13,000 square kilometers of land. Even if Allen's hummingbirds only use half of it, that leaves 6,500 square kilometers. That's a range increase over the last 45 years of 9200 percent for the sub-species, and an increase for the entire species by nearly a quarter.
Clark then argues that a highly conservative estimate would suggest that there are perhaps seven Allen's hummingbirds per square kilometer, though there could be as many as 60. That would mean there are at least 46,000 sedentary Allen's hummingbirds in Southern California today, with an annual population increase of around ten percent.
Conservationists say the Allen's hummingbird is in trouble. But are they looking in the right places at the right times?
The fact that such a relatively simple tool as eBird easily reveals the birds' population growth suggests to Clark that More there's something there. "I think the population trends are so obvious and so clear that even with these really unsophisticated techniques, the patterns pop out," he says. Garrett concurs. "I grew up bird watching in Los Angeles and have been paying attention to birds here for fifty-plus years. It has been so striking, the spread of Allen's hummingbirds and their increase in numbers."
In a sense, this analysis is a call for a more rigorous look at Allen's hummingbirds in particular, and a call to include a more diverse set of sampling techniques than the annual breeding bird surveys and Christmas bird counts more generally.
It also underscores the need to think more critically about conservation triage, or the prioritization of some species over others given limited resources, even while acknowledging potential threats to otherwise common species. "I don't know what kind of actions conservation organizations have tried to implement to help Allen's hummingbirds, but one hopes they didn't spend much effort and money," says Garrett. "There are many, many other bird species that are in far greater trouble that could use that kind of attention."