Photo by Stephen Jaquiery.
Preliminary results of an annual survey of garden birds -
which show the sparrow is the most common - suggest disease may
be taking a toll on silvereyes.
Silvereyes - also known as waxeyes - were recorded in the
greatest numbers in 2007, with an average of 10.2 per
surveyed garden, ahead of the house sparrow.
But Landcare Research scientist Dr Eric Spurr last year began
recording a decline in the silvereyes, with a slump to just
8.9 per garden last year.
He said today early analysis of the 2009 survey showed a
continuing plunge in silvereye numbers, to 6.4 per garden.
"Several survey participants commented on this decrease, and
some suggested disease was the cause," he said.
This followed reports last year of silvereyes with growths
around the bill and eyes, he said.
"The growths could be avian pox, a virus that can be
transmitted by contact with infected birds, when they
congregate around bird feeders, for example, or by ingestion
of contaminated food or water," Dr Spurr said.
Little was known about this disease in New Zealand. "Further
investigation is warranted," he said.
Silvereyes migrated to New Zealand from Tasmania or
south-east Australia about 1856, and when the first poxvirus
was identified in Lower Hutt silvereyes in 1963, scientists
said it was possible the birds had brought the disease with
Dr Spurr said this year's survey showed more birds in the
garden (12.2 per garden) than last year (11.4) and the year
before (9.4) and that the house sparrow numbers were higher
in the north than in the south.
About 1800 people created the survey through backyard bird
watching for one hour in the week to July 5.
Other preliminary results from the survey are the continued
increase in tui numbers, a large increase in myna numbers,
and a drop in greenfinch numbers.
"These changes could be annual variations rather than a
continuing trend and several more years' data will be needed
to confirm any long-term trends," said Dr Spurr.
Final analysis of the survey will be released later this
year, but the "top 10" bird species in 2009 are:
House sparrow (12.2 per garden), silvereye (6.4), starling
(3.3), blackbird (2.9), tui (1.4), fantail and myna (1 each),
chaffinch and goldfinch and song thrush (0.9 each).