by ochiai808

As the holiday season rolls in full swing and the festivities begin, Christmas decorations become delightfully impossible to avoid.  Snowmen, gingerbread families, doves, and penguins seem to pop-up everywhere amongst decorated Christmas trees, wreaths, and lights.  To keep with the spirit of the season, my blog this week will revolve around those mini-tuxedo dawning creatures, the penguins.

During three months out of the year, king penguins alternate care duties on land with foraging trips on the sea between mates.  However, king penguins live in extremely large colonies consisting of anywhere from a few hundred to 500,000 mating pairs, which poses a major problem.  Upon returning from sea, finding a single penguin in such a massively dense crowd, about 2.2 breeders per square meter, seems nearly impossible.  To make matters more difficult, king penguins lack a nest.  Instead, the mate on land incubates the egg on his feet, allowing him to move within the colony during storms or disputes with neighbors.  The resulting “short distance movement [. . .] creates an important problem in relocating one’s mate” (Lengagne et al., 1999).  The work of Lengagne, Jouventin, and Aubin aimed to study how penguins are able to handle such a problem and have found that the “difficulty in relocating mates posed by wandering incubation has been partially solved by the use of acoustic signals” (Lengagne et al., 1999).  Acoustic calls are first produced by the returning penguin as he aims to identify his mate.  His mate calls in reply, providing more information on her location within the colony.  They repeat this process until they are reunited.  In addition to the aforementioned, each pair faces difficulties due to their environment.  Not only do windy and snowy conditions drown out and degrade the sound of their calls, but the background noises due to conspecific calls with similar temporal and spectral characteristics from other calling penguins generate an extreme jamming effect.

Lengagne et al. observed 28 pairs marked for individual identification from the laying of their egg to the end of the brooding stage (when both parents leave the chick to forage for food).  The calls of each individual of interest were recorded.  While one of the penguins were out foraging for food, the calls of that absent penguin were played to its mate at a distance of 20, 15, 14, 13, 12, 11, 10, 9, 8, and 7 meters away in a randomized fashion.  It is important to note that the calls were played back in the morning during calm and dry weather.  They then noted the response of the penguin and categorized them either as positive (where the penguin calls in reply to the broadcast signal of its absent mate, interpreted as recognition of its mate’s signal) or negative (where there is no vocal response and the penguin fails to reply, interpreted as failure to discriminate the broadcast signal of its absent mate).  They also observed what they termed the Distance of First Emission, or the distance between the two penguins at the beginning of the acoustic search when the first call by the returning penguin was made.  They kept track of the Number of Display Calls emitted by the Arriving and Incubating penguins, termed NCA and NCI, in addition to the Time Delay, or the time taken between the first call of the arriving penguin and the moment of unification.

Lengagne et al. found that 71% of the incubating or brooding penguins moved, on average, a distance of 4.4 meters while their mate was away foraging (total, combining the results from both the incubating and brooding stages).  Transforming this linear distance into the maximum radius of circular areas produced an area of presence of 65.7 meters squared.  Within this area, the number of mating pairs was estimated to about 145.

Image

They also found the average discrimination distance to be 8.8 meters such that at 8.8 meters, the penguins called back in response to their returning mate indicating that there was recognition of the initial call.

Image

Image

The average distance between the two penguins when the returning penguin made his first call was 8.3 meters.

Lengagne et al. found that there were strong correlations between Time Delay and the DFE, between the NCA and DFE, and the NCA and Time Delay.

ImageImageImage

The data showed that the returning penguins called an average of 5 times over an average time of 114 seconds to reunite with its partner, and 70.17% of the time, its partner was able to discriminate the very first call of the returning penguin.

Lengagne et al. discuss how the efficiency of these uniting calls is accomplished.  The returning penguin “progresses silently towards a preferred area of the colony, named the attachment zone, probably using topographic cues” then starts its acoustic search (Lengagne et al., 1999).  However, because the individually specific calls propagates among the bodies and background noise of thousands of penguins, the broadcast distance is reduced, the signal degrades, and masking effects alter the frequency and temporal domains of the calls, which all ultimately impairs the communication process.  However, the fact that the majority of the incubating king penguins discriminate their incoming mates at their first emission implies that acoustic communication is a particularly efficient strategy in this species” (Lengagne et al., 1999).

One thing to bring up, though, is the distinction limitation of observing performance.  Just because the penguin does not respond to the returning bird (negative response) does not mean that it does not recognize its partners call.  Maybe the penguins hear their mates’ calls, however it takes energy to call back out to them (they don’t have much energy taken that they haven’t eaten for so long while their mates are out obtaining food).  Therefore, even if they hear that their mate is far away, they could wait a little longer until they know their mate is close enough so it is more likely they will be reunited.  It could be argued that this increases efficiency and energy utilization.  In addition, there is a difference between hearing their mates call as opposed to recognizing it.  The distance of 8.8 meters relates to a clear, calm, and dry environment where the main variable would be recognition.  However, if the environment were snowy or windy, it becomes an issue of whether or not the penguins can even hear each other in the first place.

Another thing of discussion revolves around their methods.  At what loudness did they play back the calls?  Although they played the calls at set distances, maybe the loudness they played it out actually corresponded to a different distance.  For example, if they played the recorded call back too loudly, having the speaker 11 meters away could actually be interpreted as the penguin being only 9 meters away.

Lengagne et al. looked at how far away the returning bird is from the brooding penguin once the brooding penguin calls back, indicating recognition by the brooding penguin.  However, I am curious to know if this is the same distance required for the returning bird to recognize the calls of the brooding bird.  Maybe there is something about moving around (by the returning penguin) that makes it different when compared to staying in one general location (the brooding penguin) in regards to hearing and recognizing calls.  When all is said and done, however, this is still an amazing feat penguins accomplish each year.

To obtain a better understanding of the difficult situation penguins are faced with, please see the following video at 1:00 (1:00 on will show you how noisy and crowded the colonies are):

Attached are some pictures illustrating just how densely populated the penguin colonies are.  The difficulties of finding ones mate can further be appreciated.

Lengagne, T., Jouventin, P., & Aubin, T. (1999). Finding one’s mate in a king penguin colony: efficiency of acoustic communication. Behaviour, 833-846.

Advertisements