When the mercury dips, people who have the option head inside. It’s fairly obvious other animals don’t have that choice quite so readily available to them. Sure, I’d be happy to share my room with a menagerie of critters in a snow storm, but I have an inkling the Steller’s Jays and Northern Goshawks wouldn’t get along so well. Communicating my willingness to share a warm room would be difficult enough, let alone trying to keep the peace.
Birds can be hard hit by bad weather. Many are well equipped for extremes, more adept at staying alive in a bad storm than you or I. A Golden-crowned Kinglet (Regulus satrapa) lives its winter on the edge of existence. To not give up the ghost, they have to constantly forage, literally right from dawn to dusk. To save time, they stop where they end up at night and huddle in a group to survive the night.
There are plenty of wonderful examples of adaptation but what happens when those behaviors aren’t flexible enough?
I haven’t forgotten we are moving ahead from Winter, but maybe you have noticed that in much of the US, we’ve had a rocky start to what people who eat food call the growing season. A little over two weeks ago here in the Sierras, the first arrivals of Wilson’s and MacGillivray’s Warblers and the typical representatives of flummoxing Empidonax flycatchers appeared. It appeared that they were in full tilt arrival and passage just as the low pressure system decided to started lobbing moisture our way.
Can you imagine a fellow running a marathon, expecting to cross the finish line to warmth and platters heaped with gluttonous portions of chocolate cake, instead finding freezing weather and hardtack? That’s how I think it might have felt to be a Wilson’s Warbler last week.
Even at 4000 feet, the Northern Sierras had snow. What exactly, does a bird who leaves here in the fall, largely to avoid nasty weather, do? Having taken a stroll to see, swaddled in garb that would have simultaneously kept the entire Shackleton Expedition warm, I can tell you one thing – they don’t bother singing.
Male birds are so hopped up on testosterone this time of year and their sole purpose is the make sure they have the best territory. The best assurance of continuous ownership is to sing incessantly. That takes care of most competitors looking to secede your land – the rest you can chase off flaunting your fitness with bright, fresh plumage, and possibly superior bulk. When birds aren’t singing at the usual times or at all, one can presume they’re otherwise occupied. Besides eating and mating, singing is the only thing a typical male songbird should be doing this time of year.
A side note: even dainty, florid warblers will occasionally resort to physical aggression when a border cannot be properly established. I watched a rival MacGillivray’s Warblers (Oporornistolmiei), chase each other over a half an hour period until they finally started making colliding. Looking exhausted, their struggle culminated in a Manzanita; wrestling with splayed wings and clacking bills. The victor flew out and immediately started singing – the loser crept out, bedraggled, retreating to what I presume was inferior scrub. Resolved.
I don’t have an answer as to what these birds are doing besides trying to hold on. When birds get desperate for food or water, either during migration or a cold snap they’ll show up out of their normal habitat and make use of unusual food sources. Here, they likely arrived with low fat reserves and found little to eat – I can’t imagine insects do much better in freezing weather but maybe that’s conjecture. Food was still around, (how do you think the Kinglets survive?), but I have no doubt there was less of it.
I found some old communications (anecdotal briefs in scientific journals) circa the 1920s, suggesting that birds might re-migrate to lower or more southerly clines when arriving early to poor weather. A communication isn’t researched, statistically proved information. After all, how does one truly study unpredictable disruptions? Still this made decent amount of sense – if it’s too cold to live, leave again till it’s better. In the Sierras, I assume that higher areas where the snow won’t melt till August won’t have successfully breeding birds this year.
Birds, feasibly along with most extant species, have taken considerable time sleuthing seasonal patterns and do a pretty good job knowing when to migrate, breed, molt, etc. Unpredictable weather creates considerable stress. In high alpine areas of Southeastern Arizona, Red-faced Warblers have been documented to simply abandon nest with the advent of late snow (at a rate of 64%!). From a temporal standpoint, that’s adaptive – a pair could die trying to nest in bad conditions. But is this maladaptive in the long term? Climate change, as most educated people should know by now (but probably don’t), isn’t just about simple warming; the seasonal predictability of weather patterns are going the way of a Jackson Pollock painting. The instinct to abandon nests when snow comes late is great in the present. But if you and that hunky warbler hubby of yours keep leaving when things get a little crazy, there’ll be less and less Red-faced Warblers for demented birders to see.
Early arrival is strongly selected for in migrating birds – the earlier you get there, the better chance you have at laying claim to better land. Birds have always run the risk of late snow or bad weather, that’s nothing new. So far as I can tell, no one knows the entire story of what happens to birds when even their best efforts to time their arrival are continually foiled. For all I know many generations of birds in the Sierras have seen this kind of event before. I doubt it was overly disastrous. Really, all I wanted to say was that I felt awfully sorry for those Wilson’s Warblers in the creek behind my bunkhouse (as I sat inside, roasting with a hot toddy and a good book).