Birds age like fine wine. During the mating season, birds with experience are in high demand as mates because they tend to be better at foraging and protecting their territory, nest, eggs, or chicks. However, in order to cash in on their experience and be desirable, older birds have to signal their age.
King penguins live in colonies where competition for territory is high and males have to defend theirs constantly. In a recent study, Hannah Kriesell et al. investigated what signals experienced king penguins use to advertise their maturity and improve their chances of finding a mate.
They investigated ornamentation and vocalization as potential candidates. The reasons for selecting these traits, as described by the researchers, are the following.
- Ornaments are known to act as honest signals of quality. For example, they may indicate parasite load, immune response or stress in birds. Both sexes of the species have bright yellow-orange beak spots, yellow-orange ear patches on both sides of the head and a breast patch of a brown to light yellow colour.
- Previous studies have found that vocalizations are sex specific – researchers are now able to distinguish sexes with 100% accuracy by analysing, exclusively, the syllable patterns of vocalization. Also, each king penguin produces a unique display call that may be used for identification of individuals and kin recognition.
“We previously identified two syllable types (‘A’ and ‘B’; Kriesell et al., 2018), and showed that adult male and female king penguins can be distinguished with 100% accuracy by the syntax of their syllable patterns, with females producing a ‘BAB’ pattern and males ‘AAB’.”
Researchers captured penguins from two breeding colonies – one in Crozet Archipelago and another in Kerguelen Archipelago, and measured parameters related to ornamentation (size, brightness, hue, chroma) and vocalization (energy, syllables, frequency). They investigated whether these parameters were associated with the age of birds, a known variable (the birds are part of a long-term monitoring program).
Ornamentation parameters (colour of beak spots, UV reflectance, size of ear patches etc.) helped the researchers accurately predict age class i.e., categorize penguins into chicks, juveniles and adults. However, these parameters were not helpful in determining age differences among adults.
Acoustic parameters of penguin calls were a lot more successful in predicting age class and age. Calls of breeding birds were found to be almost twice as long as those of non-breeders. The best predictor of age class was fundamental frequency (the lowest frequency of vocalization).
“The mean fundamental frequency of their calls decreased from chicks to juveniles and from juveniles to adults and differed significantly between males and females.”
A unique set of three parameters was strongly correlated with age for females. These were Energy (quartile Q50), frequency of maximum amplitude (intermediate syllable), and fundamental frequency (intermediate syllable). The three parameters that best predicted the age of males were tempo, frequency of maximum amplitude (first syllable), and energy (first syllable).
According to the researchers, the findings suggest that vocalization may change dependably with age and serve as honest signals of maturity in king penguins.
Read more about the study by Hannah Joy Kriesell, Thierry Aubin, Víctor Planas-Bielsa, Quentin Schull, Francesco Bonadonna, Clément Cornec, Yvon Le Maho, Laura Troudet, and Céline Le Bohec here.
