Birds and Environmental Weeds in South-Eastern Aus- Tralia

Plant Protection Quarterly VoI.6(3) 1991 137 -------------------------------- within their territories, but wiu not travel far to congregate at these new food sources. Birds and environmental weeds in south-eastern Aus There is no suggestion that any of these tralia birds prefer blackberries to native fruit, but in some areas blackberries may have in creased the total abundance of fruit. Richard H . Loyn I and Kristine French' Frugivorous pigeons in northern New I Department of Con serva tio n and Environment, 123 Brown Street, South Wales normally inhabit subtropical Heidelberg, Victoria 3084, Australia. rainforest which are now highly frag 2 School of Bio logica l Sciences, Macquarie U niverSity, Ryde, NSW 2109, mented amongst fannland. These pigeons Australia. rely heavily on introduced species in farm land (pa rticularly camphor laurel, Summary boxthom (Lycium fe rociss inJuni Miers), Cinnnmomum cnmpJwra (L.»). Presl) to pro Plants and birds depend on each other. hawthorn (Cralaeglls sp.) and peppercorn vide winter food and 'stepping stones' Here we discuss some interactions be (Sci1inlls malle L.), in addition to their usual which facilitate movement between tween birds and exotic plants. Several ex diet of mistletoe berries (Watson 1955, Frith patches of rainforest (Date el al. 1991). Mi amples sU88est that exotic plants are less 1969). grating fl ocks of silvereyes often stop for a valuable to native birds than the native In the Appendix we provide an indica few days in town gardens, where they feed vegetation they replace. However, they ti ve list of birds recorded eating exotic on fruits of exotic plants. may provide a source of food and cover plants from selected literature (mainly Birds of open woodland or farmland that attJ'3cts native birds and may now be Barkerand Ves ~en s 1989,1990), with codes make more use of weeds than birds of for important for the survival of some showing the plant parts eaten (seeds, fruits, ests, where weeds are usually less abun popUlations. These apparent benefits are leaves and o ther), the main habitat ca tego dant. Birds inhabiting highl y modified more easily observed but potentially less ries used by each bird species(forest scrub, habitats such as farmland and urban gar important than the negative aspects of open country, water or urban), and dens, usually feed largely on exotic species; change to vegetation structure and com whether the species is likely to be a seed few indigenous plant species occur in these position through weed invasion. Both as disperser or a seed predator (based on gut ha bi ta ts . The geegra phic range of bird spe pects should be considered in weed con morphology). This list indicates the ability cies may increase if they ca n adapt to farm trol. of birds to exploit new food sources and land vegeta tion. Birds are likely to play an important the Similarity of these food items to native The dietof the stubble quail now consists role in the spread of exotic shrubs and species. Native and exotic grass seeds are mainly of exo tic species, particularly agrar trees with fleshy fruit. Establishment of likely to be presented in a similar manner ian weeds. This species is likely to have these species in native vegetation may be and an adaptation for consuming one will been favoured by agricultural practices, limited mainly by competition from na be a preadaptation for consuming the though it has become extinct in Tasmania tive plants. other. (Blakers el al. 1984). In New Zealand, a sub An introduced plant can become impor species of stubble quail also prospered Introduction tant to a bird species if it provides more soon after European settlement, but is now All birds depend on plants for food or food or cover at a particular place and time extinct, for unknown reasons perhaps in cover, and many plants depend on birds than the remaining native vegetation. This cluding hunting, and burning of native for pollination, seed dispersal or insect con may be indicated when we observe more grasslands (Fa lla el al. 1987). Survival may tro l. When envirorunental weeds invade consistent or concentrated use of those not be assured simply by an abili ty to use native vegetation, we ca n expect to see plants than o f adjacent native vegeta tion. new habitats and food sources. changes in the ecology and composition of As an example, nocturnal birds such as Another ground-feeding bird, the rare the bird community, and the birds may in southern boobooks and rufous night-her plains-wanderer, has been studied in the fluence the ecology and proliferation of the ons often choose densely foliaged trees for treeless semi-arid plains of southern NSW. weeds. roosting. In many places, introduced pines Fro m fa ecal samples, its food includes in Weeds have been defined as plants in the (Pin liS spp.) or willows (Salix spp.) are se sects (40+%), grass seeds (28%), chenopod wrong place (Parsons 1976). This is a social lected in preference to the more open-cano seeds (14%) and other seeds (16%), with and political assessment based on human pied native euca lypts (e.g., at Ba rmah For 84% of the seeds being from native species criteria. For native fauna, all non-indig est, Chesterfield et al. 1984) . 11 is not known (Baker-Gabb 1988). Native plants consti enous flora has taken up space initially oc whether these birds are more abundant tuted about 73% of the plant cover in the cupied by native fl ora. Here we discuss ex than when introduced trees were absent. study area (calculated fro m data by D.). otic plant species in general, and their in To test this would require broadscale cen Baker-Gabb, personal communication), so teracti ons with bird communities. Weeds, suses of the birds before and after remov it appears that native species are preferred crops and gardens all present changes to ing the trees. by plains-wanderers. Of the grasses in fae the native landscape and affect food re In some areas of farmland, town or open cal sam pies, 8QO/o were native and 2(f/o were sources and habitat of birds. Few studies forest, thickets of exotic species can provide introduced (Phlliaris paradoxa L., Vulpia have specifically examined these interac the only source of cover for na tive birds to myllros (L.) C. Cmelin, Hordeum leporinllnJ tions in Australia . roost or nest. They are genera lly considered Link, Eragrostis cilinnensis (All.) Link ex less useful than native cover, but it is desir Vign., E. leptocarpa (A ll.) and Lelillm Use of weeds by native birds in able to establish native cover first before rigid u11I Gaud in). The chenopods were all south-east Australia removing such thicke ts. native and of the o ther plants, 78% were Exotic plants can be used for shelter, nest In many wet euca lypt forests, the great native and 22% introduced (S pergulnria ing, roosting, food or feeding substrates. est concentrations of soft fru it are found in rllbra (L.) ). & c. Pres/, Carlhamlls lallallls L. Most native birds will try a new food thickets of introduced blackberries (Rubus and Medicago polymorphll L.) . source if it becomes available in their habi spp.), and these attract temporary concen Paramo unt among the birds that use tat. Even extreme specialists such as mistle trations of fruit-eating native birds such as weeds are parrots and cockatoos, and sev toe-birds have been observed eating fruits silvereyes. Some other native birds such as era I of them have been studied in detail. of introduced privet (Ligllstrllm sp.), eastern whipbird will eat blackberry fruit They show a clear contrast between species 138 Plant Protection Quarterly VoI.6(3) 1991 that mainly inhabit forests and those that (Brown and Wilson 1984), and they mi honeyeaters are now more numerous in inhabit open country. The forest dweUing grate to Victoria and South Australia for the suburbs than in forest, e.g., red watrlebird yellow-tailed and red-tailed black-cocka winter. In Victoria, they congregate at a few and white-plumed honeyeater, and they toos generally feed on hard seeds of native sites where successive native species pro take nectar, insects and fruit from native vegetation (especially Proteaceae), and on vide food for most of the winter, but often and exotic species. wood-boring invertebrates. Outside the there is a gap in mid-winter when they Most native passerines eat insects. Insec breeding season, they also feed extensively must use introduced weeds in artificial tivorous passerines do not appear to be es on seeds of introduced pines (Pillus spp.). habitats (e.g., an introduced form of peciallyattracted to introduced weed spe In Western Australia, the short-billed form Chenapodium glallCllm L. in sewage filtra cies. Flocks of silvereyes, striated thorn bills of the white-tailed black-cockatoo also tion ponds, Plantago coronopus L. beside and varied sittellas have been observed feeds on tubers of an introduced pasture roads and Poa annua L. and chickweed feeding from aphids on deciduous trees in weed, storks biU (Erodium sp.) (Saunders (Ceraslillm sp.) on golf fairways). Natural gardens, and most bird species will take 1980). This was shown to form 50% of the foods used at that tim e have been reduced insects opportunistically from exotic birds' diet in an area of fragmented native by clearing, grazing, extractive industries plants. In general, it seems that introduced vegetation, where breeding success was and other industrial development (Yugovic plants are less favoured by native birds low, but only 10% in an area of intact veg 1984, Loyn eI at. 1986). In late winter many than are native plants, though there are few etation, where breeding success was high native species flower but the few birds that quantitative data.

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