Sleeping aggregations of bees in relation to the risk of fire at their roosting sites in a forested, suburban landscape in eastern Australia

2013·4.4 MB·English

by  P J Kubiak

Research Reports
Sleeping aggregations ofbees in relation to the riskoffire at their
roosting sites in a forested, suburban landscape in eastern Australia
PJ Kubiak
POBox439,Ryde,NSW1680,Australia
Abstract
Sleeping aggregations ofat least 13 bee species (from the families Halictidae, Apidae, Colletidae and Meg-
achilidae)wereobservedintheforestedandfire-pronelandscapeoftheLaneCoveRivervalley,insuburban,
northernSydney,NSW,Australia,duringtheyears2002-2012.Beeswereoftenfoundroostingatsitessubjec-
tivelyassessedashavingalowerrisk ofbeingburnt. Thefireriskoftheobservedsleepingaggregation sites
mayhavebeenreducedbybees: 1.roostinginsmallervegetationpatches,separatedbyaclearingfromlarger,
nearbyareasofvegetation;or2.roostinginareasofvegetationrecentlyburntbyfireandthereforeatareduced
riskofburning;or3.roostingatorneartheedgesofvegetation,givingthemachancetoescapeintoadjacent
clearedareas, ifafirearrivedwhentherewasenoughlightforthebeestoseeandflyaway; or4. roostingat
orneartheedgesof tracks ortrails,whichmightactasfirebreaksintheeventoflowerintensityfires;or5.
using combinations ofsome ofthe above four ‘strategies’. This study suggests that sleeping aggregations of
beesinthisfire-proneareagenerallyappearedtohaveatendencytooccupyroostingsitesthatwereatalower
riskofbeingburnt,orsitesthatprobablyprovidedmoreopportunitiesforthebeestoescapeanapproaching
fire.Thereareafewindicationsinthepublishedliteraturethatsomebeeandwaspspeciesinotherfire-prone
regionsoftheworldmayalsohaveatendencytooccupylowerfireriskroostingsites. (TheVictorianNaturalist
130(1)2013,22-36).
Keywords:bee, fire,sleepingaggregation, communalroost,wasp
Introduction
Communal roosting has been observed in a O’Neill 2001; Evans and O’Neill 2007). The
number of insect groups (reviewed by Yackel term generally applied to communal roosting
Adams 1999), including butterflies (Lepidop- inbeesandwaspsis sleepingaggregation’. Male
tera) (Mallet 1986; Finkbeiner et al. 2012), bees can formlooseordense sleepingaggrega-
bees andwasps (Hymenoptera) (see references tions, occasionally consisting of several spe-
below), dragonflies (Odonata) (Corbet 1999), cies and ranging from a few bees to hundreds
beetles (Coleoptera) (Pearson and Anderson ofindividuals (Rayment 1935; Michener 1974;
1985; Webb 1994), flies (Diptera) (Allee 1927) O’Toole and Raw 1991). Sometimes female
andowlflies(Neuroptera) (Gomes-Filho2000). beesmayalsobefoundsleepingnearthemales
Communal roosting has also been recorded (Rayment 1935; Linsley 1962; Michener 1974).
for harvestmen (Opiliones) (Donaldson and Typically,however,thefemalesofmostsolitary
Grether2007). bee species spend the night in nests, whereas
The males (and occasionally females) ofsoli- the males ofvarious species sleep together in
tarybeespecieshavebeenobservedoftengath- communalroosts(Linsley1958;EvansandLin-
ering in the evening to sleep together at night, sley 1960).
inbothAustraliaandworldwide (Rauand Rau Bee sleeping aggregations tend to form to-
1916; Rayment 1935; Linsley 1958; Evans and wards the end ofthe dayand, weatherpermit-
Linsley 1960; Linsley 1962; Michener 1974; ting, disband again the next morning (Evans
Houston 1984; O’Toole and Raw 1991; Dollin and Linsley 1960; Linsley 1962; Alcock 1998).
etal.2000;Alves-dos-Santosetal.2009;andsee Roosting sites maybe used by groups ofmale
images posted on the internet, e.g. www.aus- beesonsuccessivenightsforprolongedperiods
traliannativebees.com). Similar behaviour has and the same sites are sometimes used by fol-
also often been observed in male and female lowing generations ofmale bees in subsequent
wasps (Banks 1902;Bradley1908;Rauand Rau years (Evans and Linsley 1960; Linsley 1962;
1916; Rau 1938; Evans and Linsley 1960; Lins- Alcock 1998;Wcislo2003).
ley1962;EvansandGillaspy 1964; Callan 1984;
22 TheVictorianNaturalist
Research Reports
The most common type of sleeping aggre- ternally organised and do not involve co-op-
gation probably involves male bees attaching erative behaviour. However, it is possible that
themselves, either by the jaws and/or with such aggregations mightbean earlystep along
their legs, to the stems or leaves of living or thepathtowardsthemoreco-operative behav-
dead plants. Less commonly, males ofvarious iourofcomplexinsectsocieties,asindicatedby
bee species may form sleeping aggregations in Rau and Rau (1916) and Rayment (1956). Ag-
flowers, in communal burrows, under bark, in gregation pheromones may be involved in the
crevices or cracks, on seed pods and in bird formation ofsleepingaggregations inbees and
nests (Rayment 1935; Linsley 1958; Cazierand wasps (seeFreeman andJohnston 1978;Alcock
Linsley 1963; Linsley and Cazier 1972; Raw 1998; Wcislo 2003; Silva etal. 2011). Aggrega-
1976; Maynard 1991; O’Toole and Raw 1991; tion pheromones have been reported for a di-
Azevedo and Faria 2007). In denser aggrega- verserangeofnon-socialarthropods,including
tions some ofthebees mayrest ontop ofeach afewspecies ofHymenoptera (Wertheim etal.
other,withoutcontactingthesubstrate (Cazier 2005).
andLinsley1963).Oneoftheintriguingaspects Fire is important in shaping manyterrestrial
of these sleeping aggregations is that, whilst ecosystems in Australia and worldwide. Some
somemalebeesmaycompeteaggressivelywith researchers have studied the effects offire on
each other for mates during the daytime, the bee communities (Potts et al. 2003; Moretti et
same individuals can be capable ofpeacefully al. 2009;Grundeletal. 2010) andonindividual
roosting together at night (Raw 1976; O’Toole beespecies(Stowetal. 2007;MaynardandRao
andRaw 1991). 2010;CaneandNeff2011).
The reason(s) for the formation of bee and The aim of this current study is to explore
wasp sleeping aggregations have apparently whetherthere mightbearelationship between
notbeen well understood (Rau and Rau 1916; the roosting sites ofbee sleeping aggregations
Evans and Linsley 1960; Michener 1974; Dol- andtheriskoffireatthosesitesinthebushland
lin et al 2000; Wcislo 2003; Alves-dos-Santos ofnorthernSydney.
et al. 2009; Matthews and Matthews 2010). A Studyarea
number ofresearchers have put forward pos-
Observations for this study were made in the
sible explanations for this phenomenon, often
Lane Cove River valley ofsuburban northern
focusing on protection from predators and/or
Sydney,NSW, Australia. Survivingnaturalveg-
on thermoregulatory benefits (Rayment 1935;
etation in the study area includes open-forest,
Rayment 1956;EvansandLinsley1960;Linsley
and Cazier 1972; Freeman and Johnston 1978; tall forest, woodland, heathland, rainforest,
Callan 1984; Alcock 1998; Silva etal. 2011). A arinpdarsiaalntmsahrrsuhbl(aCnlda,rkmeanagnrdovBeenfsoorenst1,9r87u;shBleann-d
socialfunctionwassuggestedasapossiblerea-
sonandHowell1990;BensonandHowell1994;
son for sleeping aggregations in Steniolia obli- Martyn 2010). Muchofthesurvivingbushland
quawasps(Crabronidae)byEvansandGillaspy
t(h1e9s64e).exHpolwaenavteiro,nsithwaosulbdeeanppdeeafirnitthealtynpornoeveonf iisnstihteuaLtaedneonCosvaendRsitvoenreaarneda ihsasscbleereonphbyrlolaoduls,y
describedbyKeith(2004) astheSydneyCoast-
(seeYackelAdams 1999, foradiscussionofthe
al Dry Sclerophyll Forests. This bushland has
possiblefunction(s)andadaptivesignificanceof
undergone varying degrees of fragmentation
communal roosting in beesandother insects).
andthemajorityoftheLane CoveRivercatch-
Similar and additional explanations have been
ments naturalvegetation has been cleared, for
suggested toaccountforaggregativebehaviour
timber, agriculture and subsequently for sub-
in a wide range ofanimal species (Allee 1927;
Ward and Zahavi 1973; Stephens and Suther- ruercbeannt ydeeavresl.oApmemnotr,ewohriclehsshacsontinitgeunosuisfiebdanidn
land 1999; Stephens etal. 1999; Marzluffetal.
of bushland survives along the course of the
1996; Bell et al. 2007; Grether and Donaldson river and some of its tributaries. The largest
2007; Finkbeineretal. 2012).
areas of native vegetation occur in the upper
Matthews and Matthews (2010) considered
reaches. Introduced weed species frequently
that sleeping aggregations ofbees are not in-
Vol 130 (1) 2013 23
Research Reports
dominatethestudyareaswatercoursesandalso gregations were tentatively identified (without
disturbedplaces, such asbushlandedges. Even capturing the bees) by consulting Dollin etal.
so,thestudyareastillhasahighdiversityofna- (2000) and by referring to the identifications,
tiveplantspecies. provided by Michael Batley, ofsimilar looking
Muchofthevegetationinthisstudyareacould bees. Some bees were not identified and these
be described as ‘fire-prone’, in the sense that it are grouped together as ‘unidentified species’
islikelytobeburntquitefrequently.Thesclero- in Table 1. The number ofbees in the smaller
phyllousvegetation isthemost ‘fire-prone’, but aggregationswas counted, whilstbee numbers
areascontaining rainforestspecies, mangroves, wereestimatedforlargeraggregations.
rushland and saltmarsh may also be burnt The fire riskofeachroosting sitewassubjec-
under extreme weather conditions. However, tively assessed, taking into account character-
somepatchesofsclerophyllousbushlandinthe istics such as the proximity and density ofad-
studyareamayescapebeingburntforrelatively jacentvegetation, the amount ofleaflitter and
long periods oftime. Arson and planned fires otherfuelspresentandthelengthoftimesince
setbybushland managers (forthe purposes of thelastfire. Otherfactorsthatcouldpotentially
hazard reduction and ecological management) have modified the risk offire to the bees were
are probably the two most common causes of also noted, including whether the sleeping ag-
bushfire in the Lane Cove River area in recent gregationwassituatedontheedgeofthebush-
times. Occasionally, large wildfires have swept land area, or next to a service trail or walking
through the valley, e.g. in January 1994. Such track.Roostingsitesweregivenasubjectivefire
fires can reach high intensities, depending on riskrating,rangingfromverylowtoveryhigh.
fuel levels in the bushland andweather condi- Evenwhenrainhadrecentlyfallenataroosting
tions at the time ofburning. Smaller bushfires site, the fire risk was assessed on the basis of
occur fairly frequently in the Lane Cove River whattheriskwouldhavebeen atthesiteunder
valley. dryconditions. Itwas considered that, even in
wetter periods, bushland could dry out quite
Methods
quicklyin the event ofa run ofsuccessive hot,
In the years 2002-2012 some bushland areas
drydayswithoutrainfall.
in the Lane Cove River valley were searched
for sleeping aggregations of bees. Generally, Results
searches were conducted in thelate afternoon. Observations of bee sleeping aggregations
The first aggregation was found by chance in made during this study are summarised in
2002,whenIwasnotlookingforroostingbees. Table1.Atleast13beespecies(fromthefamilies
The pattern of searching tended to be biased Halictidae, Apidae, Colletidae and Megachili-
towards looking along walking tracks, serv- dae) wereobserved formingcommunalroosts.
ice trails and the edges of bushland because In someyears moreeffort wasput into search-
such places are easierto search. I attempted to ingforsleepingaggregationsthaninotheryears
counteractthisbiasbyalsosearchingbushland and this may largely account for variations in
awayfromtracksandtrails.Narrowtracks sur- thenumbersofaggregations found in different
roundedbythick, unburnt bushlandwere also years. Generally, the number ofbees found in
searchedandthesewereconsideredtobeavery roosts tended to peakin late springto earlyor
high fire risk situation for anybees that might mid-summer.Sometimessleepingaggregations
have been found roosting along them. Several persisted into late summer or autumn, butthe
aggregationswere found in asuburban garden numbers ofbees aggregating at those times of
in the vicinity ofthe Lane Cove River, located the year were generally smaller. Of the small
wellawayfromthenearestbushland.Afewbees numberofbeestakenforidentification,allwere
(from eightspecies)weretaken fromahandful found to be males (M. Batley pers. comms.).
oftheobservedaggregationsandsentforiden- Species from all ofthe bee families occurring
tificationtoMichaelBatley,whoalsoidentified inthestudyareawereobserved formingsleep-
some bees from photographs. However, the ing aggregations. Communal roosts ofbees in
bee species in the majority ofthe sleeping ag- the familyHalictidaewere themostfrequently
24 TheVictorianNaturalist
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Research Reports
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Vol 130 (1) 2013 25
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28 TheVictorianNaturalist
Research Reports
observed and, within this family, bees of the grassy area. Other similar examples included
Lipotrichesflavoviridis species group (probably the aggregation of Lipotriches fortior found
CL. excellent) weremostoften seen aggregating roostingonanexoticconiferinJanuary/Febru-
toroosttogetheratnight. ary2011, separatedfrombushlandbyacleared
Bees were found roosting mostly on veg- areaandalsoseveralaggregationsof?Lasioglos-
etation, including living grasses, sedges, herbs, sum peraustrale (Halictidae) that roosted on
shrubs and trees. Also, some bees roosted on treesseparatefromnearbybushland.
the skeletons ofdead plants or on dead twigs Bees sometimes roosted in areas of recently
attached to living plants. One aggregation of burnt vegetation located close to areas of un-
Lipotriches australica spent some time roost- burnt bushland. For example, in November /
ing on a wire mesh fence. Bees roosted mostly December 2002 an aggregation of Megachile
at a height ofless than two metres and often ferox (Megachilidae) bees roosted on the edge
less than one metre above ground level. A few ofanareaofopen-forestthathadbeenburntby
mixedaggregations,comprisingseveralspecies, asmallfireapproximatelyseven monthsearlier.
were observed, but most ofthe sleeping aggre- The fire risk ofthis roosting site was relatively
gationsconsistedofasinglespecies.Themajor- low because sufficient time had not elapsed
ity ofthe observed sleeping aggregations were since the recent fire for fuel loads to build up
compactordense,thatistosaythatmostofthe again.WhileM.feroxwereroostingatthissite,a
beesineachaggregationsleptincloseproximity wildfireburntalargerareaofthenearbyadjoin-
to each other, often restingin contact with one ing forest, much ofwhich had not been burnt
ormore oftheother beesatthe roost. Some of foralongtime. Thisfireburnttowithinseveral
the sleeping aggregations apparently lasted for hundred metres ofwhere the bees were roost-
a longer time than others. However, some ag- ing. Megachileferox continued to roost at the
gregationswere observed foronly one ora few samesiteforseveralweeksaftertheoccurrence
days, so the actual duration ofthose aggrega- ofthenearbywildfire.
tions was not determined. Also, the initial for- When bees roosted in places of higher fire
mation ofan aggregation was rarely observed, risktheywere often found at ornearthe edges
somostoftheaggregationsprobablyexistedfor ofthebushland.Thispositioningmayhavegiv-
sometimebeforetheywerefirstdetected. enthem thechanceto escape into the adjacent
Bees often roosted in places thatwere appar- cleared areas in the event of a fire, provided
entlyata lower risk ofbeingburnt than many that such a bushfire occurred when there was
other potential roosting sites in the surround- sufficientlightavailableandthebeeswerealert
inglandscape.Someofthebeesformedsleeping enough to fly away. Bees sometimes roosted
aggregations in smaller patches of vegetation on ornearthe edge ofwalkingtracks. Some of
that were separated by a clearing from larger, these tracks could have acted as fire breaks in
nearby areas of denser bushland. For exam- theevent oflowerintensityfires.
ple, in December 2006 a sleeping aggregation The apparent tendency to roost in lower fire
ofLipotriches australica (Halictidae) (see front risk locations may have varied somewhat be-
cover) wasfound on a relativelysmall patch of tweenspecies. Forexample, someofthesmall-
herbaceous weeds (Fig. 1) that was separated erbeespecies apparentlytendedto roost more
from the nearby larger area ofbushland by a frequentlyinplaceswitharelativelyhigherrisk
mowed,grassyclearing.Thenearbyopen-forest of being burnt. However, more observations
hadnotbeenburntformanyyearsandnobees would be required to confirm whether this is
could be found roosting in this relativelyhigh generallythecase.Nobeeswereobservedform-
fire risk bushland. Another example occurred ing sleeping aggregations at sites considered
in December 2007 when a small aggregation to be at a very high risk ofbeing burnt, even
ofLipotrichesflavoviridis (species group) bees though narrowtracks that had thick bushland
(Fig.2)roostedonPlantagolanceolata,nearthe growing on either side ofthem were searched
base ofa remnant eucalypt (Fig. 3), separated and some areas within denservegetation were
from the nearby, dense bushland by a mowed alsosearched.
Vol 130 (1) 2013 29
Research Reports
Fig. 1.Lipotrichesaustralicaroostingsite, December2006 (bees areonbandofweedsintheright
foreground).
Discussion
These observations of sleeping aggregations
over a period ofa decade indicate that, in this
fire-prone study area in south-eastern Aus-
tralia,beesgenerallyappeartooccupyroosting
sites with a lower risk ofburning. Many other
researchers have observed sleeping aggrega-
tions ofbees and wasps. Some ofthese studies
were conducted in fire-prone landscapes and
provide a few indications that bees and wasps
inotherpartsoftheworldmayalsotendtooc-
cupylower fire risk roosting sites in fire-prone
regions.
Bees and wasps roosting in sites possibly
protectedfromfire
Bradley (1908) found a large concentration of
sleeping aggregations, mostly ofwasps, but in-
cluding three bee species, in California, USA.
Hisobservationsweremadeduringsummerin
Fig. 2.Lipotrichesflavoviridis(s.g.)sleepingaggrega- theSanJoaquinValley,whenthevegetationhad
tion,December2007. beenparchedbymorethanamonthofhot,dry
conditions. The largenumbers ofwasps (and a
few bees) were aggregated at intervals along a
road for ‘perhaps amile or more’. The roosting
30 TheVictorianNaturalist
Research Reports
Fig. 3. Lipotrichesflavoviridis (s.g.) roosting
site, December 2007 (bees are in bottom
righthandpartofphoto).
groups ofwasps andbees were scattered along gathered together in a concentration ofsleep-
a narrowstrip ofdriedvegetation between the ingaggregations inthe Chiricahua Mountains,
road and a recently harvested grain field. On inArizona, USA. Thesiteoftheseaggregations
m m
the other side of the road from the sleeping wasameadow,approximately30 x90 (ca.
aggregations ofwasps and bees, thevegetation 100 x 300 feet), situated opposite a building,
had been recently burnt by extensive prairie acrossanaccessroad andcarparkingarea, ata
fires’. Bradley searched the sagebrush and fox- research station. Thebriefsitedescription pro-
tailgrassontheplains‘twelvemilesdistant’,but videdbytheauthors suggests thatthe meadow
was unable to find anyothersleeping aggrega- may have been somewhat protected from fire,
tions ofwasps. This suggests that these wasps atleast on oneside. This meadowroosting site
andbeesmayhaveselectivelyoccupiedaroost- occupied by these bees and wasps may have
ingsitethatwasatalowerriskofburning,com- served as a refuge from fires, when compared
paredwith alternativesitesontheplains. with the woodlands surrounding the research
In thispresent studysleepingaggregationsof station, which may have been more likely to
beeswere sometimes found on smaller vegeta- be burnt than the meadow. The vegetation of
tion patches, separatedbyaclearingfromlarg- theChiricahuaMountainsisproneto fires and
er, nearby areas ofvegetation. This behaviour therewasrecentlyamajorwildfireinthearea.
may have protected the bees from the greater
Beesroostinginrecentlyburntareas
riskoffireinvolved inroostinginthelargerar-
Rau and Rau (1916) foundtwo sleeping aggre-
eas ofvegetation, just as the wasps (and bees)
gations ofmale Svastra obliqua (as Melissodes
thatBradleyobservedintheSanJoaquinValley
mayhavereceivedsomeprotectionbyroosting obliqua) (Apidae) bees roosting on scorched
in a narrowroadside strip ofvegetation. Some leaves in recently burnt areas in open fields in
ofthebees observed in mystudy roosted at or Missouri, USA, but they were unable to find
neartheedgesoftracksortrails.Thismaypos- beesofthisspecies roosting in nearbyunburnt
sibly have given them some protection from vegetation. Frankieetal (1980)studiedthebee
fire, as some ofthese tracks could potentially Centris adani (Apidae) at a site, consisting of
farmland interspersed with patches ofregrow-
have acted as fire breaks in the event oflower
intensity fires. However, this would probably ing dry forest, in Costa Rica. Their study site
notapplytoverynarrowtracks surroundedby included areasofunburnttallgrassand‘brush’,
but the onlysleeping aggregation ofmale bees
thick, fire-prone vegetation. Price and Brad-
stock (2010) found evidence to indicate that thattheyfound waslocated in arecentlyburnt
roadsmaystopsomefiresinthedrysclerophyll area. In this present study, an aggregation of
Megachileferox (Megachilidae), some aggrega-
forestsoftheSydneyregion.
Evans and Linsley (1960) and Linsley (1962) tions ofLipotrichesflavoviridis (species group)
studied adiversearrayofbeeandwaspspecies (Halictidae) and one aggregation of Amegilla
Vol 130 (1) 2013 31