Dodos on a Diet

Have you ever thought a photograph made you look fat? Well spare a thought for the Dodo. According to French researchers, portraits of Dodos (Raphus cucullatus) painted by seventeenth century artists may have added quite a few kilos. In fact, some seventeenth century estimates may have doubled the birds’ weight!

A seventeenth century image of a Dodo, painted by an unknown artist.

Using measurements taken from preserved Dodo skeletons, the French team estimated the average weight of an adult Dodo at 10.2kg. In comparison, seventeenth century eyewitnesses suggested the birds weighed as much as 22.7kg (or 50lb). Contemporary paintings often show the birds as large, rotund animals, but the French researchers suggest that this was either because they were exaggerated by the artists, pictures of overfed birds, or the birds were puffing out their feathers in a display of some kind.

To derive their svelt estimate, the researchers measured the lengths of the Dodo skeletons’ femur, tibiotarsus and tarsometatarsus bones. The result was lower than other modern attempts to gauge the mass of the Dodo.

As we’ve seen many times on Hypothesis Now, using preserved remains and fossils to investigate extinct animals can only tell us so much. Given some commentators believe the Earth is in the midst of a sixth mass extinction, this just reinforces the urgent need for conservation of species and entire ecosystems. Once they’re gone, we lose vital information about our world, and there’s no way to get it back.

Incidentally, the researchers here aren’t the only ones that thinks the Dodo could lose a few kilos. A new gallery opening on the 21st January at the Natural History Museum in London will show a seventeenth century painting next to a modern image painted by one of the palaeontologists at the museum. You can find further details of the exhibition here.

Paper reference: Angst, D., Buffetaut, E., & Abourachid, A. (2011) The end of the fat dodo? A new mass estimate for Raphus cucullatus. Naturwissenschaften. On-line first 15th January 2011. DOI: 10.1007/s00114-010-0759-7

Cold weather causes female butterflies to act like males

In the animal kingdom, men usually have to persuade, cajole or bribe their way into a lady’s favour, which means the males of many species cultivate gaudy displays to attract the females’ attention. Yet for one species of butterfly, the situation is sometimes reversed. Some female squinting bush brown butterflies (Bicyclus anynana) spend their time frantically displaying the bright eye-spot patterns on their wings to as many males as they can find in the hope of attracting a mate.

A female Bicyclus anynana showing off her eye-spots. Image: William H. Piel and Antonia Monteiro/Courtesy of Yale University

The role reversal only happens when females are exposed to cold temperatures as caterpillars. According to researchers from Yale University in the USA, the behaviour change helps the female butterflies survive in difficult times: a female who manages to persuade a male to mate with her also receives a parcel of nutrients from the male, increasing her life span. This is particularly important during the cold season, when it is harder for the butterflies to reproduce successfully.

In contrast, the males’ life span is reduced once they give up their nutrient package, so they will very carefully pick the best females. In this case, the ‘best’ is the one with the brightest eye-spot patterns on her wings.

The reason males of most species regularly have to compete for the affection of females is that, usually, mating is cheap for males. Sperm are small and easy to manufacture in their millions, so males can mate with any and every female they find. On the other hand, the female’s eggs need a lot of resources to produce and nurture, so she has to make sure they are fertilised by only the fittest males around. Effectively, the females are a valuable resource over which the males must compete for access.

Very occasionally, however, these roles are reversed. The best-known example of this is sea-horses, where the male becomes pregnant and expends most of the effort required to raise the young. He therefore takes much more care over who he mates with. In the case of the squinting bush brown butterflies, a female who can persuade a male to give up his nutrient-rich gift will live longer. Suddenly the males become the valuable resource, and a prize worth fighting for.

Reference:  Prudic K.L., Jeon, C., Cao, H., & Monteiro, A. (2011) Developmental Plasticity in Sexual Roles of Butterfly Species Drives Mutual Sexual Ornamentation. Science. 331 (6013). pp. 73-75. DOI: 10.1126/science.1197114