September 6, 2011: For the first time since I arrived to Tern almost 3 months ago, it is still. The Northeast tradewinds, normally a constant presence at the atoll, are almost entirely absent. Without even the slightest breeze, it's oddly quiet today. Not only do we not hear the sound of the wind moving between antennas and solar panels on the roof, but the sound of waves crashing against the shore south of the barracks is absent. The waters outside the lagoon are glass calm and a more subtle shade of blue than we usually see.
The birds have also quieted down substantially and it feels a little eerie out in the colonies. Everybody's laying low because it's HOT out there. Gular sacs are all aflutter (at least among the boobies and frigate birds), the sooty tern flocks are in disarray without a steady wind to orient themselves by, and everybody else has flocked, literally (bad pun fully intended), to any available shade.
With Tern Island's shrub habitat in decline and roughly 30% of the island taken up by a barren expanse of compacted gravel that does not support native plants (and therefore most of our bird species), shade is at quite a premium on Tern Island. Lucky for the birds, most of the chicks are past their most vulnerable stages in their lives when they lack the physical and behavioral adaptations to handle the heat. Here are a few examples of how Tern's seabirds coped with today's high temperatures.
Frigatebirds (ʻIwa) display perhaps the most diverse (and amusing) range of behavioral responses to heat. Here are just a few of them. There's the open wing posture (apparently this reduces water loss somehow). There's gular fluttering (intensity and duration of flutter typically correlates to how heat stressed a bird is), which really requires video footage for one to fully appreciate (stay posted on this one). And then there's what I've decided to call the 'I give up' posture. C'mon, it's not that hot, is it?
Scott has been steadily amassing a pretty sweet driftwood collection for his study plot in our Active Management Revegetation Zone between the runway and the colonies. Birds are attracted to the wood every day for the perching structure it provides, but today saw especially high interest in Scott's installations for the shade they provide.
When there's a steady wind (which is most of the time) all the sooty terns (ʻewaʻewa) in a flock like this will almost invariably be pointing straight into the wind. Seriously, on a windy day these birds are as effective as any windsock in indicating the wind direction. This is another behavioral response that helps them stay cool. I imagine it also keeps the feathers nice and smooth. You'll see from this photo, however, that on a dead calm day like today nobody quite knew where to stand! A minor detail, I know, but when you share a small island with thousands of seabirds, you notice things like this.
This little dome thing here is a recycled fuel barrel being used as a shade structure. We painted it white so it will reflect heat, drilled a few holes in the sides for cross-ventilation, and then anchored it to the ground. We're still in the early stages with these designs and if you look closely, you'll see a little gizmo on the ground that looks like a thumb drive. This is a temperature logger. We are currently measuring the inside temperature of our shade structures and comparing them to the temperatures under our natural shrub habitat. If these perform similarly, we'll make more and place them out in the colonies in time for the next breeding season.
Even a simple concrete block out on the runway surface makes a difference. We're still not quite sure how this tiny brown noddy (noio) chick made it way out there, but it looks like it's been reunited with its parents and managed to find a good spot to wait out the heat!
