By Dave Houston
Declining nest numbers
Waaaaay back in 1981 I encountered my first yellow-eyed penguin on Codfish Island or Whenua Hou. 20 years later I was back on Codfish with DOC colleague Dean Nelson and David Blair of the Yellow-eyed Penguin Trust (YEPT) as part of the first ever census of yellow-eyeds on Stewart Island and its outliers. While the numbers found on Stewart Island were alarmingly low, things on Codfish looked good with 61 breeding pairs and more than 40 juvenile (1-year old) birds seen.
Eight years later Dean and I went back to Codfish with Sandy King of the YEPT to see if the decline in penguin numbers on the Anglem coast of Stewart Island was mirrored there, we took the best cooler with us fulled with goodies. A week of searching revealed only 46 pairs, down 25% on the previous count. We also saw no juvenile birds, an indication that poor food year had reduced the survival of the young birds in their first year at sea. To be sure that this was not just a temporary blip in a bad year, Dean and I again went to Codfish and searched for nests in 2011. Again, no juvenile birds were seen and nest numbers had dropped further to just 39 pairs.
This year Dean is back on Codfish on his own to see if the trend is continuing.
To the uninitiated, counting penguins seems like ‘a walk in the park’. Instead it can be a dirty, frustrating and physically demanding task. Yellow-eyed penguins nest in forest, ususally with their backs to a tree or in dense vegetation and up to 500m inland. Finding them means starting at their landing point and following the often subtle signs of a penguin track, ocassionally dotted with tell-tale penguin poop. Unlike us somewhat taller humans, penguins have no trouble negotiating the thick vegetation and seem to take delight in detouring through the thickest supplejack patches on the way to their nests, sometimes necessitating a hands and knees approach. The smell of seabird poop can alert the searcher that a nest is nearby and then close inspection of all likely looking hollows and thickets is required.
Once found, the nest is checked for eggs, the attending bird is checked for a flipper band or transponder and the nest marked by GPS and flagging tape so that the nest can be revisited later in the season to determine breeding success.
What’s going on?
Yellow-eyed penguins are long-lived (Dean just found a couple of birds he banded as chicks 20 years ago) and Codfish island is predator-free, so why isn’t it a penguin paradise? Despite good breeding success in most years, first-year survival of penguins can be very low in years when food resources are low. It seems that Codfish has experienced several of these poor years in recent times, meaning that few young birds have survived to enter the breeding population.
While adults are safe on their island sanctuary, at sea they are vulnerable to predators (mainly sharks) and by enganglement with nets set for rig and elephant fish (species most often encountered in your fish-and-chip shop). The extent of this at-sea mortality is not well understood.
And in news just in…
Dean has just emerged from the bush having found 39 nests, no change on last year (read his search dairy here). While not great news, it does confirm that last year’s low count was not a ‘one off’ low count and that something is really going on here. The continued absence of juvenile birds suggests ongoing unfavourable marine conditions. Hopefully next year’s count will start to show a positive trend.