Ecological servants

Conservation managers should not exclude native weka from their restoration projects and sanctuaries, new research suggests.

It turns out the flightless birds are surprisingly good at dispersing the seeds of native plants, an important ‘‘ecological service’’ that needs to be weighed against the weka’s occasional taste for penguin eggs or endangered geckos, concluded University of Canterbury and Department of Conservation researchers.

Weka ‘‘tend to get a bad rap. But we didn’t understand what benefits weka bring to native forests,’’ said Jo Carpenter, a University of Canterbury ecology PhD student who is also at Landcare Research. ‘‘I started this research to see if they were important seed dispersers.’’

And they are. Weka disperse about 95 per cent of seeds away from parent tree canopies, an important measure because seeds that end up too close to their parent trees suffer ‘‘disproportionate mortality’’.

It was predicted that just over half of the seeds would be deposited within 100 metres of the parent tree and a small proportion of seeds over two kilometres.

These distances compare favourably to kereru¯ , the native pigeon that is considered the nation’s ‘‘most important seed

disperser’’, Carpenter and others reported in the journal, Royal Society Open Science.

It’s even more impressive considering that weka are flightless. They are good swimmers and easily cross rivers, lakes and mountain ranges. Other scientists have recorded an adult male weka moving 35 kilometres, a juvenile moving 9km, and translocated weka moving 600km.

Weka disperse seeds so far because they keep seeds in their guts for unusually long times, in fact they have the ‘‘longest avian seed retention times yet recorded’’, Carpenter found.

To learn this, the researchers inserted tiny transponders into native miro and hinau seeds and fed them to captive weka at Willowbank Wildlife Reserve in Christchurch. The transponders’ signal was detected by a radiofrequency identification (RFID) scanner attached to the weka’s food shelter.

The tagged seeds were ‘‘easily detected inside the birds’ guts by the scanner antenna’’.

‘‘Each seed was detected an average of 10.6 times a day,’’ Carpenter reported.

The miro seeds were retained in the gut for a mean of 38.5 hours and hinau seeds for a mean of 20.5 hours. Some seeds stayed inside the birds for as long as six weeks. It’s thought the seeds were still viable.

This time data set was married to other data that used GPS devices to measure how far weka travelled.

They attached the GPS to wild weka at two camp sites near Hokitika, as well as to weka on remote Ulva Island, off RakiuraStewart Island. They tracked how far 39 birds walked over 14 days.

They also found that the West Coast weka that frequented campsites dispersed seeds 35 per cent to 40 per cent shorter distances than weka in nearby forests.

‘‘This is an example of cryptic function loss,’’ said co-author and Canterbury ecology professor Dave Kelly.

This happens when an ‘‘animal is still present in an ecosystem, but due to human impacts it’s not providing the ecosystem services that keep everything working properly’’.

‘‘We think that weka that spend more time at campsites get more food from people, and therefore don’t have to forage as far. That means they disperse seeds shorter distances,’’ Kelly said.

Please don’t feed weka, Carpenter said.

We didn’t understand what benefits weka bring to native forests.

Jo Carpenter, right