This past weekend, New Hampshire Public Radio, my preferred news venue, wrapped up their fall fund drive. I listen even during the drive, possibly out of a self-flagellating penance for not actually donating. There’s something satisying about the guilt. During the fund drive, the announcers were pushing their drawing for a free trip to Costa Rica. “Unbelievable! The biodiversity is higher than anyplace else on Earth!” You’ll get no argument from me on the merits of a Costa Rican getaway, nor on the diversity of species to be found there. But for certain species groups, the highest biodiversity comes not down near the tropics, but near the poles.
I’ve just been reading a report on Arctic seabirds from the Conservation of Arctic Flora and Fauna (CAFF) group. In it, the authors point out that the cold (though ever warming) waters of the northern oceans have historically been a nutrient bonanza on which these birds can rear their young. Now though, the convergence of the mutliple evils we’ve managed to work on our oceans appear to affecting many of these species quite profoundly.
Seabird populations are challenging to study and count. Aside from the breeding season when they come onto land, many of these long distance seafarers lead a nomadic existence and pinning down their numbers is difficult. For some species, we don’t have reliable census data even for the breeding colonies, or, if we do, only for the past few decades or so. These limitations make it hard to pick up on anything but catastrophic population crashes.
What researchers are finding now, is a disconcerting emptiness on many of the colonies. In Iceland, historically a hotbed for seabird breeding, scientists now find empty puffin burrows, eggs or dead chicks rotting in abandoned tern nests, and entire swathes of islands devoid of much bird life at all for several years running. Seabirds tend to long lives, and one or two bad breeding seasons are easily borne. But as more and more years like this pass, where the adults either return to the colony and fail to rear any chicks, or simply don’t attempt to breed at all, the consequences for the future grow more grim. These adults will continue to age and will ultimately die, even if they live 30 or 40 years before that happens. If there have been no young birds coming up to take their places, the results are clear. What still isn’t clear is why these breeding collapses are occurring. The CAFF report points to changes in sea ice, altered prey distributions, and increasing frequency of extreme weather events as possible players. A 100 year storm, after all, can wipe out many adults in a breeding population. When those 100 year storms are coming every four or five years…a population only has so much resilience.
We do know that seabirds will respond to prey availability changes by altering their foraging behavior. This graph depicts the type of prey brought back to the nest by thick-billed murres. Looking at the blue and yellow sections of each bar, we see the shift beginning in the 1990’s from the ice-associated polar cod to capelin as ice breakup came earlier and earlier in the season.
Whether or not an alternative prey is equally appropriate for rearing nestlings varies with the prey. Such shifts seem to coincide with decreases in chick survival in some species, so it does appear that one fish is not necessarily as good as another.
Pollutants in the foraging waters and in the prey are still an issue, with mercury levels in some seabirds high enough to affect breeding success, and persistent organic compounds like flame retardants and pesticides in eggs at concentrations high enough to make them unfit for human harvest and consumption. Some researchers even point out that warming oceans boost the metabolisms of the fish swimming in them, which could make them able to swim just a bit faster and evade their avian pursuers. For birds already on the thinnest of margins of survival, even an effect so slight would be piling on their troubles.
One thing is perfectly clear in reading through all these reports and into the research itself; while empty-headed commentators on the pretend news try to drum up paranoia and conspiracy theories about the existence of climate change, the scientists are keeping their heads down, scanning for the few eggs or chicks still viable, certain in the knowledge that climate change is wreaking havoc already, and we may be watching these birds disappear.