Speaking of California Endemics, Here Are Some Yellow-billed Magpies, Found Nowhere Else in the World

The Sierra Nevada is a barrier to more than just humans. Magpies "invaded" the western United States from Asia perhaps 3-4 million years ago, but the populations became isolated as the Sierra rose to higher and higher elevations, separating the Great Valley and Coast Ranges from the rest of the west. Eventually there were two races of magpie, the widespread Black-billed Magpie found across the western states from Canada to Mexico, and the Yellow-billed Magpie (Pica nuttalli), endemic only to California. There is very little mixing of their ranges.

They are entertaining to watch, and are easily seen in my area. I saw these two apparently having a quiet argument on top of a street light ("I'm not speaking to you!") on the west campus of Modesto Junior College (actually, they were just sitting and watching things; I'm not supposed to anthropomorphize animals). Most of the time they are kind of raucous.

They used to be more numerous, at times forming large flocks, but they were decimated, almost catastrophically, by the West Nile Virus. Beginning about 2005, between 50-75% of the population was killed off, until the few resistant ones could begin to reproduce in larger numbers. The birds are making a fairly decent comeback. It would have been a terrible shame to lose them.

Yellow-billed Magpies on the West Campus

One of the few birds that are truly endemic to California, the Yellow-billed Magpies (Pica nuttalli) are an elegant looking species. They have been showing up in larger and larger flocks on our west campus in the last few weeks, and making their presence known in a number of ways. Their squawking has been a nice welcome when I arrive on the campus just after sunrise. One landed this afternoon outside the window of my geology lab.

The Magpies used to flock together in the hundreds, but they were decimated a decade or so ago when the West Nile Virus arrived in California. They were especially vulnerable to the disease, and their flocking nature meant that it was easily passed from bird to bird. The population crashed in just a few years by 50%. Luckily, some birds possessed some resistance to the virus, and their numbers are beginning to recover. It's been obvious to me that the flocks near my house number in the dozens rather than only a dozen, which was the case just two years ago.

California's Endemic: Yellow-billed Magpie on the West Campus, Back from the Brink, Maybe?

California has precious few endemic species of birds. In one sense, this fact seems odd, given the many ecological "islands" in California, isolated environments where evolutionary pressures are the greatest. There are high alpine environments, desert mountain ranges with relict conifer forests, and valleys isolated by high mountain ranges, for instance. I have a feeling that the geology of the state has something to do with it the distribution of birds. There are many environments, but the orientation of the geological provinces is mostly north-south, and routes exist for birds to spread far and wide, crossing political borders into Baja and the Pacific Northwest. There are low exit points from places like the Great Valley and low passes over the margins of the Sierra Nevada. Other vertebrates can't surmount these boundaries the way flying birds can, so the trapped reptiles, amphibians and mammals show a great deal more species variation and endemism (is that a word?).

Endemic species are also vulnerable. Highly specialized species living in a single environment are subject to population disruptions when that environment is altered by the appearance of an invasive species or new disease. We've seen that on a human scale in our state. The indigenous people of the state were almost completely wiped out in the early 1800s by malaria and other diseases, with mortality rates estimated in the range of 90%. Our endemic Yellow-billed Magpies (Pica nuttalli) almost met a similar fate, and only a few years ago.

In 2004, West Nile Virus reached California and the effect on the Yellow-billed Magpie was nothing less than catastrophic. They had almost no resistance to the virus (95% mortality), and their tendency to gather in large flocks made transfer of the virus inevitable. Within two years the population crashed, dropping from an estimated 180,000 birds to 90,000. By 2007, some research suggested that the population had been halved again. Only 5% of the living birds tested displayed any kind of antibody response to the virus. That's an extinction threat.

I have memories of big flocks of the Magpies in our region, and I've not seen anything like them in my travels of the last few years. I was so very pleased to come upon a small flock when I was walking the perimeter of our West Campus on Tuesday. There were a dozen or so birds, and that is probably the largest group I've seen in some time. I saw more of them this evening in my neighborhood as well. I hope it is a good sign. They are gorgeous spectacular birds, and it would be such a shame to lose them.

I can't find any more recent data on their populations. If you know anything, please feel free to contribute to the comments!