Crane drain?

sandhill crane migration

Sandhill cranes in hiding.

(Reposted from last year.  I meant to be there this weekend, but alas, snow.)

I had it planned like a cat burglar: where would the Sandhill cranes be? when would they be where? how should I get there? when should I leave the house?  This was overkill.  It was like plotting out where in the city  I might find the rare and exotic pigeon.

I traveled out into the Sandhill crane flyway this week and realized I’d over thought it.  My first clue?  I pulled up at a highway rest stop to use the facilities and gather my bearings, and there were 30 or so in the farm field beside the rest stop.  Another twenty across the highway.

The migration paths of somewhere on the order of 500,000 cranes intersect for about a month every spring along the Platte River in central Nebraska.  The flat farm fields are littered with spilled corn and grains from last year’s harvest, and the most beautiful cleanup crew on the planet has arrived to fatten up before traveling north to nest and raise up a new generation.

Half a million sounds like a lot of birds, and it is: the shy birds scatter if you step out of the car, but treating my little coupe like a rolling bird blind worked fine (on the backroads! On the road shoulders!  Nobody is impressed with a bird blind in the middle of a major thoroughfare.)

two sandhill cranes in flightThe delight of sitting quietly and through my binoculars watching a hundred birds flying and another 50 in the field eating, field after field after field, well, I can’t share that, but I did take some videos that captured the sounds well (half a million birds make a lot of noise); I’ll postASAP.

Half a million sounds like a lot of birds, and it isn’t.  The numbers have been falling again, after decades of revival.  Though it is illegal to kill them in Nebraska, they are hunted elsewhere, (Kentucky, North Dakota, Kansas, Texas, Tennessee, New Mexico, and now Wisconsin is considering it).

The kill rates are about the same as the hatch rate.  It’s a given that the human hunters aren’t the only ones killing these birds, but adding their rates on top of what nature already had choreographed is pushing the population numbers downward again.

There’s the temptation to think “oh well, we’ll do something different when the numbers get much lower” but the latest understandings of what happened to the Passenger pigeon indicates there may be a threshold below which the birds just fall through a metaphorical trap door and disappear.

North America’s passenger pigeon once numbered in the billions, no exaggeration. Small and fast (flying up to 60 mph / 96 km), clouds of passenger pigeons would travel hundreds of miles to find the next “patch” (30 to 80 square miles was normal) of forest ready to proffer nuts and acorns and other tasty treats.  They stripped areas bare and then took off again.  Their migrations were so erradic that they wouldn’t return to a past feeding ground for decades.

As they flew overhead, in a ribbon from horizon to horizon, a person standing below had merely to point the gun up and pull the trigger: dinner.  Dinners for a month of Sundays. How could any one person do harm to such a phenomenal congregation of life?

One? No. One person couldn’t.  Every third person out there?  Yes, at that rate, harm could be done.  What really cooked their collective tuckus, however, was the commercial hunting.  Folks started following their migrations from place to place, relaying information via the fledgling telegraph service, killing, freezing, and shipping the birds to distant cities.  Kill rates jumped from 30 to 300 to 3,000, per hunter, per day.

Surely it was clear this was a bad idea, and I don’t think people are talking about commercial hunting of Sandhill cranes, but do we know enough about this bird to really say with any humility that we know enough to protect it from our collective hubris?

Group Evolution

At the same time as herding animals, flocking birds, and schooling fish use their identical markings to confuse predators (hard to focus on a target while charging), they also use their sheer numbers to protect their birthrates.

Yes, Darwin’s theory says ‘survival of the fittest’ (and he meant apt-est, not necessarily most muscular or fastest; the herd member with the wonky markings would be the one least apt, even if not the slowest), but these animals are surviving as groups, not as individuals.

As long as the collective birthrate exceeds the number of individual birds dying each year, the passenger pigeons were fine.  They lacked some of the stealth and trickery of wilier cousins and instead counted on sheer numbers.  The foxes gorged themselves, the panthers ate with abandon, the hunters shot to stuff their larders, each until it was sick to death of eating pigeons and simply moved on to other targets.

At some point, as the number of birds dying was higher than those surviving to breeding age, a crucial threshold was reached.  The population hit a nasty spiral- there weren’t enough passenger pigeons to provide cover for each other.  It became easier for hunting animals to focus on one and seize it, and harder for the flock to maintain sheer numbers past the time their predators were gorged and bored.  Re-bounding stopped being an option.

Even if they’d had little birdy orgies, the protection that the sheer numbers had provided, the capacity to produce the flip-side of mass hysteria, it was gone.  The record shows that the hunters, commercial and individual, were callous to the end, but the threshold of irreversible damage was way higher than that.

sandhill cranes cleaning the fields of waste grainIs that in the middle of happening to the Sandhill cranes?  Not quite.  They don’t have the same strategy, but their numbers may lull the same complacency from us people.  If the replacement rate is lower than the birth rate, it’s time to curb the hunting again.  It’s not about sheer numbers, it’s about change over time and our capacity to be responsible stewards of the life around us.  I think we can do this.

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