Why have house sparrows declined so dramatically, asks Bob Brockie (NZ Dompost, Monday, October 11, 2010)
Sparrows cannot live by bread alone. Chicks need protein in order to mature and survive. Based on research conducted in the UK it has been shown that sparrow chicks are starving in their nests because their parents can not find enough insects to feed them. However is this likely to be true in NZ and in other parts of the world? And is it just sparrows that are in decline?
The 2oth century biologist JBS Haldane said that “God has an inordinate fondness for beetles”. This is in reference to there being over 400,000 known species of beetles in the world, and that this represents 40% of all known insect species (at the time of the quote, it was over half of all known insect species).
According to the UK's Invertebrate Conservation Trust, at least 250 of Britain's 4,000 plus species of beetle have not been seen since 1970. This is over and above the general decline in beetles. Two-thirds of Britain's moth species have declined in the past 40 years, some by enormous amounts. Mayflies appear to have dropped in abundance by about two-thirds in the past 50 years.
This decline must be impacting hugely on birds. There are various estimates in the decline in birds, and some birds are doing better than others. RSPB conducts yearly surveys of garden birds in the UK and these surveys indicate a general decline of around 20 per cent in the last five years.
What is the situation in NZ? Are insects in decline here as they are elsewhere? We just don't seem to know, but how many years is it since we were “bugged” by insects splattered on our car windscreens? And are Mynahs still to be found up north prospecting for insects which have smashed into cars on highways? Are Mynahs in decline? Does anyone care? Just as noone cares at the disappearance of the green bell frog as it is not a native.
Generally, are our birds in decline? The OSNZ atlas which comes out every ten years records the presence of birds in any area but not whether or not there has been a decline. Garden bird surveys have been initated but have not been going long enough to tell us much yet. The native birds seem to be holding their own, probably due to increased predator control and the planting of native plant species. But will this situation last? Until we do some serious monitoring, we will not know.
For the last five years I have lived in Greytown in the Wairarapa and every summer the back door is left open, the lights on, and in all that time I have not seen a solitary huhu beetle and very few moths. How is this impacting on the morepork?
We spray the house for flies every summer and for spiders so they will not engulf the house with their webs and in doing so deprive birds, and particularly sparrows, of important protein for their chicks. We kill everything that moves in the back yard. We “clean up” our yards so that there is no refuge for wetas or other wildlife. Landscape gardeners create gardens which may have many native plants and are easy to care for but with hardly an insect, bee, or bird in sight.
District councils, golf clubs and bowling clubs use pesticides to exterminate worms on their sports fields without a thought for the impact on blackbirds and thrushes. So it goes on with species disappearing with hardly anyone noticing.
However, having said all this, sparrows in this neck of the woods anyway seem to have increased in numbers compared with two years ago, although still at very low numbers compared with ten years ago.