Larus philadelphia

Larus philadelphia, or Bonaparte’s gull. We were driving at 60 mph. Looking out the front window of the car, it was possible to see twenty or thirty gulls flying erratically overhead. As we drove forward, those gulls would disappear behind us and more would be visible in front of us. The twenty or thirty gulls probably occurred along a distance of 1000 feet or less, and we could see the gulls at this density for about 10 minutes. So if we saw 25 gulls every 1000 feet over ten miles, then we saw between 1,250 and 1600 gulls swooping and swerving overhead like swallows feeding on insects (but they couldn’t have been feeding on insects, right?) between, roughly, Saint Cloud and Big Lake, along the east (left) bank of the Mississippi River, by Route 10.

Bonaparte’s gull migrates from somewhere up by the arctic to somewhere down by the gulf (and back) every year. This sighting was not at all unusual. Starting in early fall, and again in the spring, we see giant flocks of migrating birds of one kind or another all the time, here along the Mississippi, because the Mississippi river is a major migratory pathway. We consider ourselves lucky!

Migration makes sense for so many reasons, but it is also very mysterious. For instance, migration end-points and migratory pathways may seem logical when you look at them, but when you factor in major climate change … especially glaciations … then one must contemplate a great deal of change in migratory patterns over century- and millennium-long time scales.

Also, there has for decades been evidence, accumulating on a regular basis, for the use of the Earth’s magnetic field for navigation by migrating birds. But we know that the Earth’s magnetic field is sometimes severely disrupted, changes is exact orientation regularly, and every now and then, totally reverses. What happens to migratory birds during reversals? No one knows. But we do know, or suspect at least, that many migratory birds use other information, aside from the compass built into their sensory and neural systems. They use maps burned into their brains as they follow other bird who know the routes, and they use landmarks, etc.

There are probably some very interesting reconstructions of bird migratory histories out there. I know Eton Tchernov wrote a paper on some sort of migratory California bird … an interesting case because the birds migrated from one area they could live all year to another area where they could live all year, and different populations had different start and end points that reflected a history of expanding populations size. But I’m thinking of larger scale stories, like we have with eel. Fresh water Atlantic basin eels all breed in the Sargasso sea. It matters not if these eels live in the Hudson River, the Mississippi, or one of those many European rivers that find their way so often into crossword puzzles. They all go to the Sargasso sea to breed. The thought here is that prior to the formation of the Atlantic Ocean, the vicinity of the Sargasso sea was an inland sea or large freshwater basin (probably first the latter than latter the former). Eels living here swam upstream to grow and feed, breeding in the large meeting ground of the basin that would eventually become the mid-Atlantic or thereabouts (the Sargasso sea is east of Florida, northeast of the Caribbean. Bermuda is in the Sargasso sea. The Sargasso sea is, essentially, an enormous Kelp forest.)

As the Atlantic ocean formed with the separation of the North American/South American plates from the Eurasian and African plates, the eels just kept doing what they were always doing. They adapted to the salt/fresh water boundary problem along the way, presumably.

But enough of eels, I want to return to random thoughts and tidbits about birds and migrations …

Eurynorhynchus pygmeus

There is current news of a bird in trouble in Siberia. It is Eurynorhynchus pygmeus, the Spoon-Billed Sandpiper. Owing mainly to predation on eggs laid in the Russian province of Chukotka (predation by canids) this species has experienced a precipitous drop in numbers. There may be as few as 200 breeding pairs left. You can find out the details of this horrific story here. Is this a case of a bird paying the cost of the downside of migration? Home court advantage often has benefits that are hard to explain but easy to measure. If your breeding grounds are not where you live all year round, maybe you loose this advantage. Things you could be doing year round to increase the security of nesting sites are not possible.

Migration can get you in trouble in other ways. If all the Yahoos living in Big Lake and Becker Minnesota happen to decide to go out shooting during the Bonaparte’s Gull migration, they could have wiped out a percent or two of the species (and expended a lot of ammo doing so). Of course, this would be illegal, and they would get in trouble. But over hunting (for food, mainly) seems to be the best explanation for the extinction of what was once one of the most common bird species in North America, if not the world: The Passenger Pigeon. If hunting regulation and a certain degree of gun control was not in place, species like Bonaparte’s Gull would be cooked geese, as it were.

Well, just the other day, there was a massacre affecting a migratory bird species in Cyprus. This was the gregarious red-footed Falcon of Europe. Being a gregarious raptor is pretty rare. Raptors being somewhat grouped up while migrating is less rare. In this case, 52 of the falcons were shot by yahoos in Cyprus. The bodies of the birds and the expended shotgun shells were discovered last Friday. Details here.

There is something being done in Eurasia to address problems like this:

International awareness of the plight of migratory birds of prey and owls across Africa and Eurasia is set to get a major boost this month. Countries from China to South Africa will gather in Scotland under the chairmanship of the UK and United Arab Emirates, aiming to draw up a new agreement for concerted international conservation action.

This is the first of two planned meetings, at which governments will work alongside key conservationists under the auspices of the international Convention on Migratory Species (CMS).

The process is driven by findings two years ago that 50% of migratory birds of prey in the African-Eurasian region have a poor conservation status and many are showing rapid or long-term population declines.

[source]