Archive for January 2014
Today is Penguin Awareness Day, and what better way to celebrate than recapping a visit to some great penguins (and their awesome keepers). Recently I ventured out Jenkinson’s Aquarium in New Jersey. While interacting with penguins is always worthwhile, this trip is tied to a research project aiming to get better estimates of the sizes of extinct penguin species. Paleontologists have long been aware of “giant” penguins in the fossil record, but the estimates for their sizes have fluctuated wildly. Old sources proposed that some species were up to six feet tall, which we now know is a gross overestimate. The tricky part is that some fossil penguins had very different skeletal proportions than modern species, so it is not safe to just “scale up” any one bone. For example, we know from nearly complete skeletons of Kairuku that the humerus was longer compared to the rest of the body than in modern penguins, whereas the coracoid was shorter. If we tried to guess the height from just the humerus, we’d end up with a bird roughly five feet tall, versus a height of just over three feet if we instead scaled up the coracoid bone. The truth lies in between – reassembling the skeleton suggests the extinct penguin’s height was about four feet and two inches in “normal” pose.
At the aquarium, two fine birds named Dunlop and Kringle offered some perspective. These two are part of the aquarium’s colony of Black-footed Penguins (Spheniscus demersus). With the help of penguin manager Reagan Quarg, I collected measurements of their standing heights. With these measurements (and many more from other penguins), we hope to calculate the range of variation in extant species. One thing we have emphasized is that there is no single standing pose for penguins. Depending on their mood and the temperature, penguins may stand tall with their neck mostly extended, or hunch down like a grumpy child. The penguins at the aquarium showed quite a range of heights. Dunlop measures about 20 inches to the top of his head (not counting the beak) when reaching for a treat but only about a foot tall when hunched over.
In the northern hemisphere, winter is in full swing and snow has begun to accumulate in many cities. If you think braving the icy wind to get your driveway cleared of snow is a challenge, consider the struggles of the Emperor Penguin. Emperor Penguins not only survive the Antarctic winter, during which temperatures drop well below freezing and winds whip to gale-force speeds, but manage to complete their breeding cycle in this incredibly harsh environment. The amazing abilities of these birds to survive extreme conditions has been well documented by scientists and filmmakers. Nevertheless, there is still more to learn. A recent study by Dr.Dominic McCafferty of the University of Glasgow and colleagues in France showed that Emperor Penguins actually drop their surface temperatures below air temperature and get a sneaky benefit from doing so.
Penguins need to stay warm to survive, and also to incubate their eggs and warm their hatchlings. Thus, their core body temperature stays at about 37C (about 98F), in part due to their system of counter-current heat exchangers. While the core stays warm, however, temperatures at the extremities can plunge – in effect the penguins “turn off” heat flow to the flippers and feet to minimize overall heat loss. In the study, researchers used infrared imaging to measure the temperature of penguins in a breeding colony and find out how different parts of the body surface varied in temperature. During the measurements, air temperatures were a bone-numbing -17.6C (0 F). Unsurprisingly, the warmest parts of the penguins in these images were the eye and beak region and the flipper, which are two regions that are not wrapped in thick blubber (or lined with feathers, in the case of the beak). The rest of the body offered a surprise though – much of the penguin’s surface dropped below the ambient air temperature! In fact, many regions reached levels below freezing. The team concluded that this paradox may serve a useful purpose. Penguins are constantly losing heat through radiative heat transfer because their core temperature is so much higher than the surrounding temperature. They slow this process through the insulating effects of blubber and feathers, and by huddling with other penguins, and also burn the fuel of stored fat to generate metabolic heat. Heat can also be transferred by convection, and this is where the sub-zero plumage comes into play. Heat can be harvested by convection from any air that is warmer than the plumage. As the Antarctic air swirls around, packets of air that are above the plumage temperature will sometimes come in contact with the penguin and in these cases the features can absorb a bit of the difference. The amount of heat gained by this phenonomen appears to be very small, but in extreme environments every bit helps.
McCafferty DJ, Gilbert C, Thierry AM, Currie J, Le Maho Y, Ancel A. 2013. Emperor penguin body surfaces cool below air temperature. Biology Letters 9: 20121192.