An international team of researchers from New Zealand, Australia and Denmark have recently published research revealing new evidence of how the moa (large, long-lived ratites) were hunted to extinction.
Intense human predation
The research, published in the 2 October 2012 issue of Quaternary Science Reviews, examined moa remains from several significant 13th–15th century archaeological deposits across the east coast of the South Island, from Marlborough to South Otago. DNA analysis of remains revealed that humans commonly ate moa eggs. Over 50 of the giant birds’ eggs were identified at one site at Wairau Bar – a number that likely represents a considerable proportion of the total reproductive output of moa in the area and emphasises that human predation of all life stages of moa was intense. The analysis also revealed that humans were more than twice as likely to catch male birds as females.
In their published paper, the researchers write, the “human colonisation of New Zealand in the late 13th century led to catastrophic impacts on the local biota and is among the most compelling examples of human over-exploitation of native fauna, including megafauna. Nearly half of the species in New Zealand’ s pre-human avifauna are now extinct, including all nine species of large, flightless moa (Aves: Dinornithiformes). The abundance of moa in early archaeological sites demonstrates the significance of these megaherbivores in the diet of the first New Zealanders.”
Analysis of 251 out of 323 eggshell fragments and 22 out of 27 bone samples from the various archaeological sites revealed the remains of four moa species: Anomalopteryx didiformis, Dinornis robustus, Emeus crassus and Euryapteryx curtus.
Moa under extreme reproductive stress
As moa were likely slow reproducers with small clutches, the researchers write that the level of exploitation observed could have put the moa under extreme and unsustainable reproductive stress. “The intensity of moa egg collection shows that moa were exploited heavily at all life stages, combining to accelerate their extinction.”
The researchers were also able to tell what sex the birds were using a technique called ‘molecular sexing’ of the bones. In contrast to previous ancient DNA studies from natural sites (rather than archaeological/man-made sites) the researchers observed an excess of males – compared to the consistently reported excess of female moa at natural sites. This suggests that males were preferential targets.
Excess of male moa at archaeological sites
“The excess of males may indicate an easier access to this sex. There could be several reasons for this, including males being slower, smaller and perhaps less timid. An alternative explanation is that, as with other ratites, male moa were likely the primary incubators of the egg(s) and would therefore have been extremely vulnerable to predation from the moa-hunters.”
“It could be argued that paternal incubation was favoured in moa in order to reduce the risk of accidental egg breakage, given that female moa were up to 200% heavier than their male counterparts.
“Considering that this is the first time that moa sex ratios have been analysed from archaeological sites, the male excess we observed is intriguing, but additional bones from other archaeological sites will need to be sexed and dated to confirm if males were indeed preferential targets.”
The researchers are now calculating the age of the various bone and egg fragments to try to work out the relative contribution of predation on moa birds and eggs in their study of extinction dynamics.
The researchers in this article are not sure why there were an excess of male moa in the sites they have analysed, so they give several possible reasons. This is an example of the tentative nature of science. Your students may like to try this activity, which will help them understand the self-correcting nature of science, the tentative nature of scientific knowledge and science as an on-going endeavour.