Wednesday, December 1, 2010

‘Scout bats’ are a myth

To justify killing flying-foxes, some fruit growers and politicians peddle the myth of ‘bat scouts’ (see below for more examples). Like honeybee scouts, bat scouts are said to search the landscape for new food sources and guide their fellow bats to them. So, they claim, if a fruit grower can shoot the alleged scouts, the orchard remains a secret to all other bats.

It’s a convenient myth for fruit growers because they can claim they only need to kill a few scouts to protect their orchards from vast numbers of flying-foxes. Queensland MP Rob Messenger asserted that “most farmers only needed to take a maximum of ten scouts in order to protect investments worth tens of thousands of dollars”.[1] Federal MP Bruce Scott told parliament that flying-foxes weren’t a problem for Queensland farmers when shooting was permitted as “the scout bat … [can] be terminated—quickly and humanely”.[2]

But the scout notion is biologically bogus [3] and it is fanciful to claim that fruit growers protect their crops by killing just a few flying-foxes when so many have been slaughtered in the past.

Peddling the myth: claims about ‘bat scouts’

Before damage mitigation permits were revoked by the city-centric Queensland Labor government, the flying foxes did not pose a problem because the DMPs allowed for the scout bat, which is the bat that looks for a new roosting place for the colony, to be terminated—quickly and humanely.
Bruce Scott, Federal Member for Maranoa, 22 November 2010 [4]

The fruit growers in the Granite Belt are asking the Queensland Government to temporarily reinstate damage mitigation permits. These permits would allow fruit growers to minimise the damage to their orchards by controlling the number of fruit bats who scout for food prior to an invasion by the main colonies.
Senator Barnaby Joyce, 18 August 2009 [5]

We're not talking about the wholesale shooting of bat colonies, but the selective deterrence of lead scout bats that will deter bat colonies from coming into an area.
Mike Horan, Shadow Queensland Primary Industries Minister, 24 July 2008 [6]

Like many other fruit growers, Ms Ferris advocates shooting the 'scout bat', the lead flying fox which apparently flies ahead of the flock, alerting others to the location of food.
    The Government has repeatedly stated that the scout bat theory cannot be proved and has little basis in science.
    But fellow district grower Ian Mungall is also a strong believer in the concept and told QCL earlier this year he had watched how scout bats called other flying foxes into his orchard. He could only watch helplessly as they devoured large swaths of his nectarine crop resulting in losses of $20,000.
Queensland Country Life, 24 November 2009

Flying-foxes don’t need a ‘bat scout’ to find food

With good vision and sense of smell, long-distance navigation skills, and an excellent memory for locations, each flying-fox has the ability to find its own food.[7] They undoubtedly gain information about local food sources by observing other bats but there is no evidence for a special category of bats that generously seek out food on behalf of others.

Flying-foxes are not sharers

Bats aren’t like ants or bees; they don’t live in organised cooperative societies with designated roles.[8] They are territorial about food and can spend much of the night defending their patch in a food tree from others (the reason for all the bat squabbling heard at night).[9] A flying-fox has much to gain if it can find a fruit tree all its own. It makes no sense to suggest that a designated few would search out food for the rest of the camp.

Orchards are easy to find

Orchards are much easier to find than natural food sources such as isolated fruiting or flowering trees in forests. They are very concentrated sources of food that stand out in the landscape as a regular array of trees, easy for a bat to spot from the air and easy to smell when fruit is ripe. Many orchards are close to flying-fox camps and couldn’t be missed.

Bats have a good memory for food sources

Flying-foxes have an excellent memory for locations.[10] Some return each year to the same branch in a bat camp after many months away. They are not likely to forget an orchard they have fed in previously, so there would be no need for a scout to find each orchard all over again at the beginning of each fruit season. Whether or not flying-foxes choose to feed in an orchard depends on what other food is available. When natural foods are in short supply, orchards are heavily targeted.[11]

Shooting is not a practical solution

There is no practical way for fruit growers to effectively protect their crops by shooting small numbers of flying-foxes.[12] They cannot spend all night every night guarding their orchard and be guaranteed of shooting every bat that enters. A NSW survey of 17 growers found that on average they shot for just 1.6 hours/night for 3 nights a week for 4.4 weeks, leaving their orchard unguarded for more than 90% of the time.[13] Shooting a few bats is particularly useless when natural bat foods are in short supply and orchards are heavily targeted. This is when the majority of fruit losses occur. Netting offers full-time protection and is the only method known to be effective, which is why it is the industry standard.

The scout bat theory hasn’t worked in the past

Fruit growers haven’t been able to protect their orchards in the past by killing a few alleged scout bats, which is why a large proportion of commercial fruit targeted by flying-foxes is now under netting.[14] It flies in the face of history for growers to contend that they need kill only a few flying-fox scouts to protect crops, when it was common past practice for a grower to kill hundreds or thousands a season.[15] Growers complained they couldn’t protect their crops when governments reduced the numbers of flying-foxes permitted to be killed (due to declining populations). Now that shooting bats has been banned in Queensland and could be in NSW (as recommended by a government-appointed independent panel),[16] it suits some growers and politicians to peddle the scout myth in an attempt to justify ongoing shooting.

Shooting is inhumane and anti-conservation

When bats are shot at in orchards at night, it is inevitable that some are wounded rather than die immediately, and because the ripening of most commercial fruit coincides with flying-fox births, shooting results in the starvation of babies when their mothers are shot.[17] There is no way of making shooting humane, which is why the Queensland Government has banned it.[18]

Shooting also puts pressure on declining flying-fox populations. Because flying-foxes don’t breed successfully until they are 2 or 3 years old and have only one baby a year, they have a low capacity for population growth.[19]  Two species killed in orchards – grey-headed and spectacled flying-foxes – are listed as nationally threatened.[20]

Shooting flying-foxes for crop protection is inhumane and anti-conservation. Killing mythical bat scouts won’t help growers protect their crops. The scout myth rather than mythical scouts should die.  


[1] Messenger R. 2009. Government must change flying fox policy now to stop disaster. Media release 12 January.

[2] Scott B. 2010. Environment Protection and Biodiversity Conservation (Public Health and Safety) Amendment Bill 2010. Second Reading. House of Representatives Votes and Proceedings. Hansard 22 November 2010, page 33. 
[3] There is no published evidence for bat scouts – a search of scientific databases found no references – and it is inconsistent with knowledge of bat behaviour. 
[4] Scott, 2010. (See note 2)
[5] Joyce B. 2009. Flying foxes and fruit in Queensland’s granite belt do not mix. Website for Senator Barnarby Joyce.
[6] Horan, M. 2008. Quoted in Hendra virus: Qld’s bat policy ‘out of touch’. Queensland Country Life 24 July 2008. 
[7] Eby P. 1995. The biology and management of flying foxes in NSW. NSW National Parks and Wildlife Service, Hurstville. Hutcheon JM, Kirsch JAQ, Garland T. 2002. A comparative analysis of brain size in relation to foraging ecology and phylogeny in the Chiroptera. Brain, Behavior and Evolution 60: 165-180. Safi K, Dechmann DKN. 2005. Adaptation of brain regions to habitat complexity: a comparative analysis in bats (Chiroptera). Proceedings of the Royal Society (Biological Sciences) 272: 179-186. 
[8] Bat camps or colonies do not constitute a discrete or fixed population of flying-foxes. Some bats may be resident in a camp, others are regular or sporadic occupants. There is considerable population flux in bat camps mostly related to the availability of food. Flying-foxes can travel thousands of kilometers a year between different camps. 
[9] Hall L, Richards G. 2000. Flying Foxes: Fruit and Blossom Bats of Australia. UNSW Press, University of NSW.
[10] Safi and Dechmann, 2005. (see note 7).
[11] NSW Flying-fox Licensing Review Panel. 2009. Report to Landscapes and Ecosystems Conservation Branch, NSW Department of Environment and Climate Change. 10 May 2009.
[12] A survey of 17 fruit growers in the Sydney Basin by Dang et al. (2009, see note 13) found that 88% of them did not believe that shooting ‘scouts’ (early arriving bats) was effective at deterring others and most believed that flying-foxes returned to the orchard after being scared off. 
[13] Dang H, Jarvis M, Fleming P, Malcolm P, Brook J, 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 and NSW Department of Environment and Climate Change. 
[14] According to the Queensland Department of Primary Industries (2005), about 90% of lychee, longan and rambutan growers in North Queensland had netted their orchards by 2005. According to Dang et al. (2009, see note 13), netting on the north coast of NSW covers 100% of stone fruit orchards (61 ha), 67% of lychee orchards (30 ha), 100% of blueberries (430 ha), 50% of custard apples (200 ha) but none of bananas (1728 ha) or mangoes (180 ha). In the Sydney Basin, 30% of surveyed orchard area was netted  (89 ha of 296 ha). The NSW Flying-fox Licensing Review Panel (2009, see note 11) reported that about 23% of stone fruit and apple orchards in the southern sector (450 ha total) are netted.
Queensland Department of Primary Industries. 2005. Nets save lychee industry from flying fox and bird attacks. Media release, 16 February 2005. 
[15] A federal court judgment [Booth v Bosworth] found that one fruit grower probably electrocuted 18,000 spectacled flying-foxes in one season. From 1986-1992 more than 240,000 grey-headed flying-foxes were shot in orchards under 616 licences in NSW; many more were shot illegally. Wahl (1994) reported that 69% of orchardists surveyed said they had shot without a licence or outside licence provisions. 
Wahl D. 1994. The management of flying foxes (Pteropus spp.) in New South Wales. M. App. Sci. Thesis. Applied Ecology Research Group. Canberra. 
[16] NSW Flying-fox Licensing Review Panel, 2009 (see note 11).
[17] Divljan A, Parry Jones K, Eby P. 2009. Report on deaths and injuries to grey-headed flying-foxes, Pteropus poliocephalus, shot in an orchard near Sydney, NSW. 
[18] AWAC. 2008. Animal Welfare Advisory Committee’s Recommendations. Advice to the Minister for Primary Industries and Fisheries The Honourable Tim Mulherin. 
[19] Martin L, McIlwee AP. 2001. On the intrinsic capacity for increase of Australian flying-foxes (Pteropus spp., Megachiroptera). Australian Zoologist 32: 76-100.  
[20] Grey-headed flying-foxes and spectacled flying-foxes are listed as vulnerable under the federal EPBC Act.  Currently, NSW still permits the shooting of flying-foxes (which includes grey-headed flying-foxes) but Queensland no longer permits the shooting of any flying-foxes (which includes both grey-headed and spectacled flying-foxes) for crop protection.