Birds in apple orchards: a Miner pest?

Can farming techniques foster biodiversity, or even help fix some of the problems like invasive pests? A few ideas regarding apples and birds.

Bacchus Marsh is known for its apple orchards. They are uncaged, and scare guns are the main tool (that I’m aware of) to keep birds such as the Sulphur-Crested Cockatoos from smashing the crop. In West Australia, the endangered Baudin’s Black Cockatoo can be a major pest in apple orchards, sadly a contributing factor to its endangered status. Both species are seed eaters: they tear open the apples to eat the seeds inside, a very frustrating behaviour for the farmer.

Nevertheless, in many cases, (other) birds provide an essential service in eating insect pests, as just published by Charles Sturt Uni researchers Rebecca Peisley, Dr. Manu Saunders and Prof. Gary Luck. An alternative to managing destructive  birds with guns (lethal or scare variety) is cages. Orchardists around Harcourt (central Victoria) use them: huge rolls of fine black plastic mesh covering the whole orchard. I was happy to see that, according to the paper by Peisley & co, smaller birds (not Cockatoos) often get under these nets and find a safe haven inside the orchard:

Between early fruiting and harvest, the apple trees in the two Harcourt orchards were covered with drape netting (excluding the open branches used in this experiment) and this appeared to provide a haven for many small bird species (e.g., striated thornbills (Acanthiza lineata) and yellow-faced honeyeaters) which could fit  under gaps in the net, while excluding most larger parrot species and birds of prey

Their paper compares benefits vs costs of birds in apple orchards, but my main interest is in the cages and the invasive native bird, the Noisy Miner (not to be confused with the similar-ish looking Myna, an unrelated, exotic pest species).

I haven’t seen many Noisy Miners around Bacchus Marsh, but this native bird is a top order pest across the country (PDF factsheet here). It is an aggressive, colony-forming species that chases away a large range of smaller native birds, and it seems to thrive in particular kinds of  disturbed ecosystems like the edges of bushlands, linear roadside vegetation, trees around grazed areas on farms, and the suburbs. Mainly, larger birds like Magpies and parrot species are the only ones that seem to co-exist with it.

Not only does the Noisy Miner cause the disappearance of small birds like scrubwrens and pardalotes, and many smaller honeyeaters, but the absence of all those smaller insect-eating birds can mean trees suffer much greater insect attack. This can contribute to dieback, a killer of trees in many rural areas.

So the cages might have another use, besides keeping parrots out. I’ve observed this first hand while tending the orchard on my Dad’s farm. He has his apple orchards caged with chicken mesh, which has holes large enough for many small bird species to pass through (but not Noisy Miners: they are too big). Inside the cages, whilst spraying Bordeaux mix (about the only spray used on his apples) I noticed a lot of nests of small birds among the branches (I didn’t spray the nests!).

61
An apple orchard cage (pic taken from a non-OHS-approved perch atop the farm windmill)

Around the house and sheds, a plethora of small native birds forage in the Eucalypts and garden. Almost no Noisy Miners show up there – although a couple of hundred metres away, on the linear strip of trees along the road, they were plentiful. The smaller birds have a safe refuge, and perhaps the inability of the Miners to drive them away leads the Miners to simply leave the area alone.

There are other possible factors contributing: the state forest, probably an inhospitable environment for Noisy Miners, is only a hundred metres or so behind the house, and perhaps this contributes to the diversity of small birds. But I think the frequent sight of small birds’ nests in the apple trees, in the cages, probably does say something.

This slideshow requires JavaScript.

References

Peisley RK, Saunders ME, Luck GW. (2016) Cost-benefit trade-offs of bird activity in apple orchards. PeerJ 4:e2179 https://doi.org/10.7717/peerj.2179

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s