A couple of days ago while on Ulva Island with guests we met up Robin researcher Cayley again.
She was busy as usual tracking Robins, who at this time of year are in the middle of nesting. She had just fed a male, who in turn was busy chatting up a female.
We had a chuckle as the gifts he was “wooing” his lady with were actually mealy bugs supplied by Cayley. Robins are opportunistic feeders, much as are Robins world wide, and will come to any disturbance on the off chance bugs will be disturbed.
The researchers use this habit to feed birds and then track them to the nest, where the juveniles are banded.
As an aside, our forest birds are remarkably tolerant of nest disturbance, and if done sympathetically, seldom abandon a nest.
The program calls for every nest to be visited, and every bird to be ringed and recorded. A big call on an island of 600 acres. But they do it, or at least as far as my observations go, as I can’t ever remember an un-banded robin.
A spin off from this is that we have a very precise handle on the robin population each spring. This is of great interest, as a year ago last August the Department of Conservation (DoC) undertook acontroversial aerial rat eradication program on Ulva Island using the toxin Brodifacoum.Controversial, because New Zealand has a very vocal anti-poison lobby and one of their platforms for opposition is that aerial poisoning operations do huge damage to native birdlife. DoC expected to lose around 40% of both the Robin and Saddlebackpopulation. And counts by the Robin Researches in the nesting season post that operation bore this out. However that season was also a very successful breeding season for Robins, and meant that at the end of the summer, the population was estimated to be around the same overall number as at the end of the previous summer. (before the poisoning operation).
So talking with Cayley was an ideal opportunity to ask her what the population was looking like now. She told us that at that stage she had 190 pairs recorded… 380 birds, with probably more to find, and on top of this were non breeding birds. Her own view was that the population was more or less the same now as it wasimmediatelypre-poisoning. These figures absolutely give the lie to the anti-poisoningpropaganda that would have us believe that Ulva Island would turn into an avian desert. We have no figures other than non scientific visualassessmenton Saddleback, but my observations at least would indicate much the same end result as the Robins. An loss of population of species other than Weka, Robins and Saddleback has been so low… if any…. as to be non observable. The reason for this is that Robins and Weka feed exclusively on ground insects, which themselves are unaffected by brodificoum, but do become toxic and so are vectors for secondary poisoning. Weka took toxic ratcarcassesas well….. and Saddleback are significant although not exclusive ground insect feeders. Several other species are occasional ground feeders, but not sufficiently so to have any appreciable effect on numbers.
Certainly there was a high loss of weka, a loss that could have been minimised by capturing weka pre-operation, and re liberating when safe to do so. DoC chose not to do so, but have release a dozen or so birds from Bench Island, who have already bred successfully. This liberation addresses a genetic bottleneck thatoccurred back in the 1990’s when the initial rat eradication took place.
Horror predictions by anti-poisoning campaigners that the soil and therefore the insect population would be forever toxic, and that bird losses would continue at a very high rate into theforeseeablefuture are absolute nonsense, and the figures from the research done so far completely vindicate the decision to do the operation. Yes some species did take a hit, but a successful breeding season effectively meant that for one year the overall population was more or less static, and this year we will go back into a normal population growth, until optimum numbers are reached.
New Zealand is a world leader in animal eradication programs such as has been used on Ulva Island, and in fact Ulva was one of the first successfully undertaken. The operation last year was the first ever attempted on an emerging rat population, and was very much a “suck it and see” trial. That it was successful is enormously heartening for those involved with wildlife protection.
For background on Ulva Island follow this link to our Ulva Island web page, and in particular you may wish to read an article lower down on that page.