Lethal crop protection is not effective

Farmers can safely protect their crops from flying-foxes and birds with canopy or tunnel nets. Netting is the only consistently effective method; nothing else  works when native food supplies are in short supply and there is strong flying-fox pressure on crops.  A large proportion of Queensland orchards are now fully or partially netted, including an estimated 90% of lychee, rambutan and longan orchards in north Queensland.[1] Unfortunately, those who remain un-netted or partially netted can kill many thousands of flying-foxes a year.

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A peach orchard with full exclusion netting - Image: Nancy Pallin.

The effectiveness of netting 

If flying-foxes cause significant losses in an orchard, it makes economic sense to net. Growers who net their crop commonly recoup their costs within a very few years due to fruit saved from flying-foxes and birds. According to the Queensland Government’s Lychee Information Kit, netting may be cost-effective even if only small crop savings are achieved.[2]

The Queensland government provides concessional loans for netting through the Queensland Rural Adjustment Authority.[3] Netting can be done in stages, using profit earned from saved fruit to fund subsequent stages.

If crop losses are generally low, and it is not cost-effective to net, there are other non-lethal options such as noise and light deterrents that may work to minimise incursions. Some growers find them effective. But flying-foxes can become habituated to deterrents, limiting their effectiveness.

Many fruit growers oppose lethal methods of crop protection, and would prefer that their industry promotes a clean and green image. They recognise the increasingly strong public expectation that food will be produced without cruelty to animals.
“We do not agree with the shooting of native birds and bats. It may seem like an easy way out but it does little to improve profitability. Nets have saved our crops and therefore our profits 100 per cent.”
                                                  John Gough, stonefruit grower [4]
“Orchard netting provides a physical barrier to exclude flying foxes and protect crops under all conditions. While sound and light systems can be used to deter animals from feeding in an orchard, these systems can be ineffective in some situations (e.g. when animals are starving).”                                                                                                                Queensland Government [5] 

Why killing is ineffective 

Shooting and electrocution were the two lethal methods previously approved for crop potection against flying-foxes in Queensland. See here for more information about electric grids.

Even when there were no limits to the numbers of flying-foxes that could be killed, orchardists frequently claimed large fruit losses. Most fruit damage occurs when native foods for flying-foxes are in short supply, and killing does not stop damage in orchards under high flying-fox pressure.

Farmers can’t patrol their entire orchard all night every night and kill all or even most bats that enter. A NSW survey found that farmers on average spent just 1.6 hours a night, 3 nights a week, guarding their orchards.[6] Even if they kill a few dozen early in the night, many more flying-foxes can arrive to feed later in the night. Similarly, electric grids kill only a small proportion of flying-foxes that enter an orchard. 

The quota system in place for six years prior to Queensland’s ban on shooting allowed on average 0.5-1 flying-fox (of each species) to be killed every night in an orchard.[7] Although many growers complained that the quota system did not allow them to protect their crops, some now claim that killing a small number of flying-foxes is effective because it allows them to kill so-called scout bats.

Do 'scout' bats exist? Some growers contend there are certain flying-foxes whose role it is to search out food sources and then lead other bats to it (like honeybees). They claim that if they shoot these ‘scouts’ they can avoid damage because other flying-foxes won’t find their orchard. 

But there is no scientific evidence for bat scouts.  While flying-foxes are highly social and undoubtedly learn from each other, the scout idea is inconsistent with what is known about the capacity of flying-foxes to find food.[8] 

As a very concentrated source of food and an obvious feature in the landscape (from a flying bat view), orchards are easy to find – far easier than scattered fruiting or flowering trees in a forest. Flying-foxes have an excellent memory for places, allowing them to return to the same branch in the same tree in a camp after months of being away, which would allow them to return to orchards they had previously seen or visited. They don’t need a ‘scout’ to find them.    
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Currently banned in all states; lethal electric grids over crops in North Qld. (Image: C. Booth)
More than 90% of surveyed NSW farmers reported that shooting early arriving flying-foxes was not effective at deterring others and that flying-foxes would return to an orchard after initially being scared off with gunshots. [9] 

This is an arial view in north Queensland, showing orchards  next to rainforest. From a flying bat view, the orchard would be easy to find, much easier than occasional fruiting trees in the forest nearby. (Google Maps).

Leave ineffective cruel crop protection in the past 

Killing for crop protection in Australia has a long history. In 1929, biologist Francis Ratcliffe was brought from England to investigate the ‘flying-fox problem’. He noted in his report after a two-year investigation that the object of most orchardists suffering damage was for the most part “to kill as many flying-foxes as possible”, and he documented the variety of ways by which destruction was attempted:
  • Shooting – “expensive and ineffective” 
  • Strychnine poisoning in orchards – “partially successful” 
  • Poison gases (chlorine, hydrogen cyanide) in flying-fox camps – ineffective 
  • Introduction of an infectious disease – unsuccessful 
  • Explosives – “complete failures” 

However, Ratcliffe concluded that the “assumption that the flying-fox is a menace to the commercial fruit industry of Australia is quite definitely false, and cannot be cited as a valid reason for the expenditure of public money on its control.” [10]

What farmers with netting say

Duck Creek Mountain Fruit, Alstonville NSW (2008) (full PDF download here)

We found the practice [shooting] totally ineffective, as were noise machines and flashing lights.

 

In 1990, we netted our entire stone-fruit orchard with 48mm netting. In the following year the profits from our protected crop paid for the netting structure erected that year. ...

 

With netting over our orchard we have peace of mind during the harvest; no damage to the fruit from flying foxes, birds or possums - and we are preserving our wildlife. Stone-fruit is a profitable crop when grown under netting. The cost of the netting structure is well and truly cost-effective.

 

Stone fruit grower, John Gough, Wollongbar NSW (2008) (full PDF download here)

[Netting] has saved our crops on several occasions, giving us a very competitive edge. This year we got top price for our fruit in a market where many orchardists had been wiped out by hail.

 

Case studies in To Net or Not to Net

  • Before the orchard was netted, 40% losses to flying fox and birds were normal. After netting, there was no loss of early fruit and no delay to harvesting noted. Fruit quality is improved Early fruit in the top of tree is not lost and this fruit gets the best prices.
  • Prior to netting, 70% losses to parrots were incurred. Fruit ripens more evenly under the net. Shade from net reduces sunburn on fruit. Wastage at packing was 20% before netting but is now only around 4%.
  • Without nets 20% or more losses to birds and flying foxes would be expected in a ‘normal’ year. The nets are good for public relations. Nets bring the business to the attention of the public, which increases farm gate sales. Fruit quality is improved as fruit is allowed to hang longer and develops a better flavour.

Netting costs & returns

The capital cost of netting an orchard can range from $17 000 per hectare up to $72 000 per hectare.

The financial returns from orchard netting include:   
  • Income from the sale of fruit normally lost to pests or hail (some growers estimate average crop losses of 60%)
  • The harvest and sale of earlier fruit from the top of the canopy, which has a high value and is often lost to birds and flying foxes
  • The quality and value of fruit harvested from netted orchards may be higher than fruit harvested from non-netted orchards
  • Higher yields can improve picking speed and reduce harvest labour costs. Less sorting is required, which reduces the cost of picking and packing
  • Netting removes one of the elements of uncertainty in orchard management, allowing more reliable crop forecasting and budgeting, and potential access to more lucrative markets
  • Income from netted orchards is more assured
  • There is need for night patrols to check on flying fox activity
  • Appropriate netting will control some insect pests, potentially reducing or eliminating insecticide costs.

Queensland Government (2008) ‘To Net or Not to Net’  
References
[1] Department of Primary Industries & Fisheries (2005) Nets help save lychee industry from flying fox and bird attacks.Media Statement, 16 February 2005.
[2] Menzel C, Kernot I, Chapman L, Rigden P. (2002) Lychee Information Kit. Department of Primary Industries, Queensland Government.
[3] See http://www.qraa.qld.gov.au/.  
[4] See weblink to this PDF document 
[5] Rigden P. (2008) To Net or Not to Net. Queensland Government.  
[6] Dang H, Jarvis M, Fleming P, Malcolm P, Brook J and McClelland K (2009) Grey-headed Flying-foxes (Pteropus poliocephalus) in Orchards: Damage Estimates, Contributing Factors and Mitigation. Final Report to Hawkesbury Nepean Catchment Management Authority. NSW Department of Primary Industries, Orange and NSW Department of Environment and Climate Change.  

[7]Under the quota, damage mitigation permits could be issued to kill up to 15 Spectacled flying-foxes, 20 Grey-headed flying-foxes and 30 Black flying-foxes per month per orchard.
[8] See "Scout Bats Are Myth" for more information & references.
[9] Dang et al. See footnote [vi]
[10] Ratcliffe F. (1931) “The Flying Fox (Pteropus) in Australia: Report of cooperative work conducted on behalf of the Council for Scientific Research, the New South Wales Department of Agriculture, and the Queensland Home Secretary’s Department”. Council for Scientific and Industrial Research Bulletin No. 53.