Making Things Aukward: The extreme life history of amazing Arctic avifauna Alle alle
When one weighs less than 200g, life above the 66th parallel could never be anything other than extreme. When considering the sheer array of environmental challenges facing the Little Auk (Alle alle), it almost begs the question of how they could possibly have evolved in the first place. However these highly-derived and hardy members of the Alcidae family eschew human preconceptions and are in fact one of the most successful and numerous seabirds on the planet.
Trials by Ice
Little auks (or dovekies as they are also known) grow to be approximately 20cm long and weigh a maximum of 180g giving them a relatively large surface area compared to their internal volume, over which to lose a lot of heat. Thermoregulation therefore is of critical importance. Moreover, as dovekies breed on islands in the high arctic, from Baffin Island in Canada to Franz Josef Island north of Siberia, their chicks also must be adapted to frigid temperatures; especially as for the first 3-4 days after hatching chicks remain poikilothermic (extremely vulnerable to internal fluctuations in temperature). Studies have also shown that A. alle chick development is negatively impacted by adverse weather conditions and unfortunately, the high Arctic is rarely synonymous with picnic-weather.
Fortunately, adult little auks have a high field metabolic rate and low thermal conductance, thanks to thick water-proof plumage and a layer of fat beneath the skin, all of which means that they lose heat slowly in both aquatic and aerial environments.
In terms of chick survival, dovekie chicks whilst still in the nest attain the highest levels of fat of almost any seabird. Adults also choose to breed in boulder fields and scree slopes meaning that chicks are generally sheltered from the elements unlike some of their alcid cousins.
Little auks are also masters of timing. In the last few years, in response to climatic variation the breeding season and median hatch date of chicks has shifted earlier in the year to remain in the optimal longest days and warmest temperatures of the year.
(Energy) Bank of Mum and Dad
Having evolved for feeding by diving little auks have very high wing-loading (a heavy body weight in relation to their wing size) and their characteristic fast-flapping flight results in a high metabolic rate. Adults therefore must consume 80% of their body mass in plankton a day to maintain their systems, somewhat compounding the issues of brooding an egg and foraging for a dependent chick for an extended period of time. This study found that adults invest so much time and energy into raising a single chick a year that their own body mass and immunocompetence decreases over the breeding season.
To combat this adults mate for life and on average live to an age of 16 years giving themselves plenty of opportunity to replace themselves in the population over the course of their lifespans.
The parents take it in turns to incubate the egg and chick for a short period after hatching giving their partner a chance to feed. To maximise efficiency, they adopt a method of bimodal feeding, alternating several short trips with the more occasional long trip. It has been postulated that they make short trips to feed the chick as often and quickly as possible and use the longer trip to forage for themselves. Also, although the incubation period and fledgling stage of the young is relatively long for seabirds, adults only bring 15% of their daily catch back to their chicks which consequentially fledge from the nest when they have only attained 60% of the adult’s body mass.
Armies of Auks
Little auks also face considerable pressure from predation, particularly during the breeding season. The glaucous gull (Larus hyperboreus) are far more aerially adept, polar bears (Ursus maritimus) are able to feed on 32 little auks a day and seabird chicks form the majority of an arctic fox’s (Alopex lagopus) diet during the summer months. Even humans eat little auks- an Inuit delicacy called kiviaq. However dovekies overcome this issue once again with their unimpeachable sense of timing. Taking part in mass synchronised breeding, little auk colonies, although difficult to census accurately, can be from 1000 to millions strong, improving the probability of their fledging chick’s survival with nature’s age-old paradigm: safety in numbers!
Feeding in Darkness
In addition, a commonly overlooked challenge facing all seabirds feeding in high latitudes in the winter is the necessity of foraging in darkness. Until recently it was assumed that the amount of zooplankton in Arctic waters decreases significantly in winter months, however the feeding behaviour of little auks demonstrates that this is patently not the case. Moreover their stomach contents show that they are selectively choosing their prey, not simply hunting in the dark catching any species available. How do they locate zooplankton blooms in darkness and how do they catch specific prey in dark water? Unfortunately there has been little research into the senses of A. alle. It may be that they use light from the moon, stars or aurora or even daylight reflected from below the horizon; or alternatively they may locate their prey through using olfactory senses like other seabirds.
Climate Change Chronicle 167,892: The Copepod Catastrophe
Finally, as though the Arctic climate was not already inhospitable enough, A. alle, like all polar fauna are facing threats from climate change. Their primary food source is the large copepod Calanus glacialis which is found only in cold Arctic water however as a result of melting sea ice altering polar currents the influx of warm Atlantic water around their breeding sights in Svalbard is reducing the availability of the larger copepod and replacing it with a smaller species insufficient to support the breeding colony’s population. This impact is not limited to Svalbard but also impacts the East Greenland Current and the breeding colonies situated on the coast there and as adept as auks are at adapting, it is unclear how even they will react to this most prevalent Arctic threat.