Shedding Light on Blue Duck

Forest and Bird, Volume 20, Issue 4, 1 November 1989, Page 2

Shedding Light on Blue Duck

Gerard Hutching

O NE OF THE FASCINATING QUESTIONS that has exercised the minds of wildlife scientists recently is whether the vulnerable blue duck can fly out of one catchment into another. The answer to that has important implications for the long term survival of the torrent birds. If they are restricted to one catchment, the birds stand to suffer from over population within their catchment, or human modification of their habitat could have dire consequences for that particular population. For some time now it’s been believed that blue duck were destined to remain within the catchment where they were born. However, DoC scientist Duncan Cunningham believes otherwise and has good evidence to suggest blue duck can disperse across watersheds into other catchments (a watershed is a high point from which water flows away into different catchments). He gives the example of a blue duck that was spotted recently on a log on a saddle in the Kaweka Range, apparently heading for a new catchment. In addition there are 34 records of blue duck sighted high up on South Island mountain tarns, presumably also looking for a new river to move to in the next catchment. Most of these were seen between December and April; one theory is they were juveniles pushed out of their birth territory. One way to resolve the debate is through blood testing of populations which should show whether birds in areas far distant from one another are widely similar or different in their makeup. DoC has started to carry out such tests.. One of the major findings of the distribution survey carried out by Cunningham is that

blue duck are most common in areas which humans have not modified. Because most blue duck now live within the DoC estate, in theory there should be less danger of habitat destruction than in the past, and therefore hopes are high that numbers may increase. A question that researchers and managers are wrestling with now is to decide whether to capture lone blue duck far from sizeable

populations and use them for captive breeding, or whether to take ducks from large populations for captive breeding or leave them alone. Sometimes it can be difficult to ascertain whether in fact the blue duck is a lone one, in which case a breeding pair may be broken up.