Light raindrops pattered against the tarp stretched above my head. Deep inside my tank top, t-shirt, long-sleeved shirt, sweatshirt, and jacket, I shivered. The damp cold of the day had made its way insidiously through my layers of clothing, freezing me from the inside out – and we had only been sitting here for two hours, meaning we had at least six more to go. I sighed, resigning myself to a(nother) cold, clammy, uncomfortable day.
Most field biologists have spent at least a few days freezing their butts off in the field. Unfortunately for me, however, being cold is not something I’m particularly tolerant of. And in this case, the deep chill seeping into my bones was somewhat unexpected – because most people don’t go to Hawaii to be cold.
As we’ve mentioned before on this blog, field biologists often get a unique perspective of the places where they work. So while bikini-clad tourists lay tanning on the beach less than 50 km away, I spent most of my time in Hawaii clad in at least three layers of clothing, huddled on the northeastern slopes of the Big Island’s tallest mountain, Mauna Kea.
As it happens, Mauna Kea is not just the tallest mountain in Hawaii – it is, in fact, the tallest mountain in the world (depending on how you look at it). From its base on the sea floor, it rises over 33,000 feet – almost 1,000 feet higher than Mt. Everest. Of course, only 13,802 of those feet actually rise above the surface of the ocean – but it’s still a lot colder at thirteen thousand feet in the air than it is at sea level. The top of Mauna Kea is frequently snow-covered in winter, and spending a rainy day hanging out on its slopes can be a chilly experience.
No one mentioned this aspect of Mauna Kea to me before I took the job – or, indeed, filled me in on the fact that our field accommodations were luxurious in every way except one: they had no heat. And so I spent a great deal of my time in Hawaii shivering. (In fact, I was once so cold that I tried warming my hands over the open flame of our gas stove. This backfired when the sleeve of my sweatshirt caught fire – but for just an instant, before I extinguished the flames in the sink, all I could think was, “Wow! My hands are finally warm!”)
However, while the damp, misty chill of the Hawaiian forest was perhaps not ideal for field biologists (at least, not for me), it turns out that it’s pretty important for the organisms we were there to study: the birds.
I went to Hakalau to work as a field assistant on a long-term study examining population trends of Hawaiian forest birds. Although just about anyone would be excited to be spending the winter months in Hawaii, I was excited for an entirely different reason than most people: Hawaiian honeycreepers are one of the poster children of adaptive radiation.
Arising from a single, unspecialized ancestor species, Hawaiian honeycreeper species have exploded to fill multiple ecological niches on the islands. There are finch-like honeycreepers and parrot-like honeycreepers and warbler-like honeycreepers. And then there’s my particular favourite: the ‘akiapola’au – which we nicknamed the ‘Swiss Army knife bird’. ‘Akis fill the woodpecker niche in the Hawaiian forest. They use their straight, strong lower bills to drill holes in tree bark, and their long, curved upper bills to probe those holes for insect larvae.
It’s one thing to learn about adaptive radiation in a lecture hall…but quite another to see its results, firsthand, in the field. Honeycreepers may not be the quintessential example of adaptive radiation – that honour being reserved for Darwin’s Galapagos finches – but they are (with all due respect to Darwin) definitely one of the most dazzling. My first day at Hakalau, I was constantly distracted by flashes of colour, as the deep scarlet of an ‘i‘iwi or the bright orange of an ‘akepa flitted through the nearby ‘ohi‘a trees. Seeing their endless, beautiful forms brought evolution to life for me in a way that four years of undergraduate biology textbooks never had.
Unfortunately, however, Hawaiian birds are not just the poster child for adaptive radiation. They could also be featured on posters for another buzzword concept in biology: multiple stressors. Hawaiian birds are currently under attack from every side…and, more often than not, they’re losing the fight.
The plight of Hawaii’s forest birds started – as these stories so often do – when humans showed up, changing habitats and trailing with us the usual host of desired and not-so-desired biological companions. From rats and house cats to feral pigs, non-native bird species, and mosquitoes, humans unleashed (sometimes intentionally, but more often unintentionally) a tidal wave of invasive species that swamped the delicate balance of life on the remote Hawaiian islands.
While each of these invasive species individually has a negative effect on Hawaii’s native birds, it’s in concert with each other that they become especially dangerous. Some of the introduced bird species on the island arrived there carrying avian malaria, a blood parasite that is relatively common in most places, but foreign to Hawaii. The introduced mosquitoes acted as vectors to transfer that parasite to the native birds – which had never been exposed to it, and hence were completely lacking any defences. Even the feral pigs got in on the act, digging up roots in the forest and inadvertently creating hollows which filled with water, providing ideal breeding sites for mosquitoes. It’s a multi-pronged attack, and one that has resulted in the decimation of many of Hawaii’s native bird species.
But these native birds do have one thing going for them – the cold. Mosquitoes are largely restricted to low elevation areas of the islands (~5000 feet), as their larvae don’t develop properly at the lower temperatures found further up the slopes. So high elevation forests, like those found at Hakalau, have for decades acted as refuges for Hawaiian honeycreepers.
And therein lies yet another problem: we all know, as the climate warms, that cold places will not necessarily stay cold. In Hawaii, climate change is yet another stressor for the birds. Increasing temperatures will likely mean the end of these high altitude refuges, and even more dramatic declines in honeycreeper populations, as has been documented in recent studies on the island of Kaua’i. Slowing the rate of climate change may be the only hope for some of these already beleaguered species.
As I’ve already mentioned, I’m not very good at being cold – in fact, it makes me decidedly grumpy. But while I was in Hawaii, watching an ‘i‘iwi feed on the bright pink flowers of an ‘ohi‘a or an ‘akiapola’au hammering holes in the bark of a koa tree more than made up for the damp chill. Without the cold, I might never have had the chance to see these spectacular and declining species. That realization alone was enough to make me almost appreciate the shivering…except perhaps for the day I caught my sleeve on fire.