Frigatebirds are a family of seabirds which have a scope for strong sexual selection. This due to the striking ways that males attract females and that through observation in a study population, only 55% of males successfully obtained a mate. The species used for the study was the Magnificent frigatebird, Fregata magnificens.

When females are looking for a mate, they fly around male display sites and look for that bright red pouch being inflated by the males. This is the gular pouch that males present along with a drumming sound. When females are inspecting, males turn their body to makes their pouch look as big as possible and produce loud and deep drumming sounds. As it may be difficult for females to accurately assess the males due to height or the way the male is positioned, it was thought that there was a relationship between pouch size and the frequency of the drumming sound and that the pouch acts as some kind of resonance chamber.

69 males were assessed during their courtship, their pouch sizes noted, and their drumming sounds recorded for analysis. It was found that there was a negative correlation between the two variables. As the size of the pouch increased, the frequency of the drumming sound decreased thus providing evidence to support the hypothesis that the pouch acts as a resonance chamber. This correlation suggests that, as the females might not be able to accurately see the pouch size, the frequency of the drumming sound helps them get an idea and therefore helps them make their decision.

Reference

Madsen V, Balsby T. J, Dabelsteen T & Osorno J. L. (2004). Bimodal signaling of a sexually selected trait: gular pouch drumming in the magnificent frigatebird. The Condor, 106(1), 156-160.

One of the most remarkable animals in the animal kingdom is the Superb Lyrebird (Menura novaehollandiae). Its ability to mimic the sounds of a variety of species is nothing short of astonishing. The males use their vocal ability, along with their flashy tail, to attract potential mates. In fact, up to 70% of their vocalisations consist of imitations from up to 20 local species of bird.

It has been thought that females are impressed by the repertoire of sounds that a male can produce. This hypothesis does seem plausible in the case of M.  novaehollandiae as his repertoire is quite extensive however, for other species of bird, this is not the case. A new hypothesis is not how large a repertoire is but how accurate the mimicry of the sounds is.

A study from 2012 set out to test just how accurate the mimicry of M.  novaehollandiae is. They assessed the accuracy with which the lyrebird was able to imitate the complex song of the Grey shrike-thrush, Colluricincla harmonica. The accuracy of the imitation was found to be extremely strong and the only deviation came from the fewer amount of repetitions that were produced by the lyrebird. It was so accurate that it was able to fool the grey shrike-thrush itself.

This idea of accuracy being driven from female preferences has also been examined specifically and with the use of spectrograph cross-correlations, they were able to provide ample evidence to support this alternative hypothesis to the previous repertoire idea.

References

Coleman S. W, Patricelli G. L, Coyle B, Siani J & Borgia G. (2007). Female preferences drive the evolution of mimetic accuracy in male sexual displays. Biology Letters, 3(5), 463-466.

Dalziell A. H & Magrath R. D. (2012). Fooling the experts: accurate vocal mimicry in the song of the superb lyrebird, Menura novaehollandiae. .Animal Behaviour, 83(6), 1401-1410.

This week I am talking about an artistic fish that creates elaborate, and time consuming, pieces of artwork to impress and attract females. This artwork was discovered by divers in 1995 and it wasn’t until 2011 that scientists were able to say who or what created them. It was a small male puffer fish Torquigener sp.

Many marine animals are known to create nest sites on the seafloor however; the puffer fish creates unique characteristics not found anywhere else in the ocean. Radially aligned peaks and valleys that are created outside the actual nest site; the peaks are decorated with shells; and the sand is altered to create irregular patterns in the nest site itself. These patterns were created before mating and after a female has visited the site, they collapse. Females were found to evaluate the artwork and make their mate choice based on the nest construction, although what exactly they look for in a nest site is still unknown.

The specific patterns created provide more than just an aesthetic function. The radially aligned peaks that the fish constructs aids in providing lots of soft sand that can be deposited in the nest site.  The males flap their fins in order to dig up the sand and create the valleys and peaks. Also, due to fluid dynamics, and the construction of the outer nest, the sand that the fish stirs up will be propelled towards the centre of the nest and not outside it so the males efforts are not done in vain.

References

Kawase H, Okata Y & Ito K. (2013). Role of huge geometric circular structures in the reproduction of a marine pufferfish. Scientific reports, 3.