April 18, 2018, University of Canterbury
A new study about New Zealand's extinct moa, involving acid baths and concrete mixers, by researchers from the University of Canterbury and Landcare Research, has revealed a surprising finding about their ability to disperse tree seeds.
For decades it had been assumed that New Zealand's largest native fruits evolved to be eaten and spread about prehistoric landscapes by the large extinct moa. The new study, published today (18 April) in the prestigious Proceedings of the Royal Society B, casts doubt on this theory.
By examining the seeds found in 23 preserved moa gizzard samples, and 152 ancient moa droppings, the authors have shown that although moa consumed some of New Zealand's largest fruits (up to 15mm diameter), their muscular, stone-filled gizzards pulverised all but the tiniest of seeds. Only seeds less than 3mm diameter were found in the droppings and were therefore capable of being dispersed by moa.
Lead author, University of Canterbury (UC) Ecology Ph.D. student Jo Carpenter says that part of the reason people had assumed that moa dispersed the large seeds – such as from miro, mataī, hinau, pōkākā, and pūriri trees – was due to the thick seedcoats, potentially requiring severe abrasion (as would have occurred in the stone-filled gizzards of moa) for rapid germination.
"These seeds seem poorly adapted for dispersal by birds that are alive today," Carpenter says. "We were amazed to find that even silvereyes, which are one of New Zealand's smallest fruit-eating birds, can disperse seeds significantly larger than the giant moa were dispersing."
To confirm their suspicions, the researchers subjected miro and hinau seeds to a simulated passage through a moa gut, by tumbling the seeds in a stone-filled concrete mixer followed by bathing in a warm, weak acid bath. They found that this treatment did not actually increase the speed of germination as had long been suspected. In fact, the seeds still took between two and seven years to germinate.