Sixteenth Australian Weeds Conference The role of native birds in weed invasion, species decline, revegetation and reinvasion: consequences for lantana management Peter J. Turner and Paul O. Downey Pest Management Unit, Department of Environment and Climate Change, PO Box 1967, Hurstville, New South Wales 1481, Australia Email: [email protected] Summary The threat posed by Lantana camara L. benefiting from invasion, including 89 birds which use ( lantana) to native biodiversity has recently been as- lantana for habitat or as a food source (DECC 2007). sessed nationally. Part of this assessment identified 113 Whilst lantana is considered to provide a lower native bird species associated with lantana infestations, quality habitat than uninvaded native communities with 24 directly threatened; 68 positively influenced (see Crome et al. 1994, Smith et al. 1998), the birds (or benefited) by lantana invasions; and another 21 that utilise lantana can cause a conflict between their species threatened but also partially benefiting (e.g. conservation and the management of lantana (see from additional food resources) from lantana inva- discussions within Crome et al. 1994 and Gosper and sions. Of the bird species that benefit from lantana, Vivian-Smith 2006 on the conflicts that can arise). 28 are reported to consume lantana fruits as well as For example, lantana has become an important part of the fruits and seeds of a range of native plants, some the diets of rainforest pigeons, (Recher et al. 1995). of which are also threatened by lantana. However, lantana fruits are in many ways similar to Information on the fruits and seeds consumed by many native fruits (Gosper and Vivian-Smith 2006), these 28 bird species can be used to determine the role thus birds may feed on lantana fruits as well as those of of birds in native plant species declines, revegetation, native species. This can result in the dispersal of viable and invasion processes. For example, 202 native plant lantana seeds (Liddy 1985) into native communities. species that produce fruits and seeds which are con- In the past, weed management strategies have of- sumed by these birds are also threatened by lantana. ten failed to acknowledge these animal-weed interac- Thus these birds may have indirectly contributed to tions (Lawrie 2002). Yet, to manage weeds effectively, native plant species decline through the dispersal of such interactions, especially between weeds and their lantana into native communities. In addition, such ac- dispersers need to be known. However, each disperser tions could hamper restoration efforts with the birds may be simultaneously involved in interactions with continuing to disperse lantana as well as another 36 multiple species (Buckley et al. 2006), including both weed species, which have been observed to invade weeds and native plants. In addition, there are a range following the control of lantana. of flow-on effects which are not well understood. Such information is critical for developing long- Therefore, this study aimed to determine (i) which term weed management strategies for biodiversity native bird species eat lantana fruit, (ii) which other conservation, as well as understanding the role and native and alien plant species produce fruits/seeds implications of bird dispersal. As native birds play that are consumed by these bird species, and (iii) the a role in dispersing both native and alien plants, it likely consequences of these interactions for weed will be important to encourage native plant recovery, management and revegetation. Information such as while controlling weeds that will continue to invade this is critical not only for determining revegetation over the long-term. and restoration targets, but also to determine possible Keywords Conservation, dispersal, frugivores, reinvasion patterns in managed sites. Lantana camara, restoration, weed substitution. MATERIALS AND METHODS INTRODUCTION The Weed Impact to Native Species (WINS) assess- Despite lantana invading more than 5% of the Austral- ment process (see Downey 2006) was used to deter- ian continent (Sinden et al. 2004), until recently little mine the biodiversity threatened (as well as benefited) was known about the native biodiversity threatened by lantana invasion. These results, as well as informa- (Turner et al. 2007). A recent national assessment of tion on other alien species that could invade or increase the threat posed by lantana, revealed 1246 native plant in abundance following lantana control, are presented and 141 native animal species as being at risk from in DECC (2007) and Turner et al. (2007). lantana invasion (DECC 2007, Turner et al. 2007). A A list of the native bird species that have been re- further 142 native animal species were identified as ported to consume lantana fruits was compiled from the 30 Sixteenth Australian Weeds Conference literature (e.g. using HANZAB Volumes 1-7, including previously as the data on these interactions has not Marchant and Higgins (1990); and Barker and Vestjens been available. (1989), Food of Australian Birds). The full reference The dispersal of lantana by birds while also list is available from the authors. The fruits and seeds of foraging on native species, may have indirectly con- other plant species that these birds also consumed (also tributed to native plant declines (Figure 1), as some determined from the above references) were compared of these plant species are reported to be threatened by with the plant species identified in the WINS process lantana invasions (DECC 2007, Turner et al. 2007). (see above). Only plant species that produced fruits and seeds that these particular birds consumed and were identified from the WINS process as being threatened Table 1. Native plant species at risk from lantana by lantana were included. In addition, other major weed invasion and the number of native bird species that species associated with lantana (see DECC 2007), that consume their fruits/seeds as well as lantana. produced fruits and seeds consumed by these birds Native plants threatened by lantana No. of bird were identified. It should be noted that it was assumed species that the consumption of fruits and seeds by these birds Melia azedarach L. 16 could result in the dispersal of the plant, irrespective Ficus rubiginosa Desf. ex Vent. 15 of its effectiveness. For example, some birds such as Polyscias elegans (C.Moore & F.Muell.) Harms 14 rosellas destroy most of the seeds as they feed. Acmena smithii (Poir.) Merr. & L.M.Perry 13 Ficus macrophylla Desf. ex Pers. 13 RESULTS Ficus obliqua G.Forst. 13 Twenty eight native bird species were identified to Ficus watkinsiana F.M.Bailey 12 consume the fruits of lantana. These birds have also Alphitonia excelsa (Fenzl) Benth. 11 been observed to feed on the fruits/seeds of 202 of Glochidion ferdinandi (Mull.Arg.) F.M.Bailey 11 the native plant species identified to be at risk from lantana invasion using the WINS process. On average, each of these bird species fed on the fruits/seeds of Table 2. The top seven bird species based on the 24.7 ± 4.3 (SE) native plant species. Approximately number of weeds they consume; and the number of 60% of these birds consumed the fruit/seed of the na- native plant species threatened by lantana that they tive plant, Melia azedarach L., highlighting a large also utilise. degree in dietary overlap between them (Table 1 – the Bird species that consume No. of alien No. of native top nine species). fruits/seeds plant species plant species These 28 bird species also consume fruits/seeds Silvereye 19 23 of another 36 weed species, which can invade follow- Pied currawong 13 37 ing lantana control. Again there was a high degree of (Strepera graculina Shaw) dietary overlap, with approximately 60% consuming Lewin’s honeyeater 12 64 wild tobacco (Solanum mauritianum Scop.); and 54% (Meliphaga lewinii Swainson) camphor laurel (Cinnamomum camphora (L.) J.Presl) Figbird 12 43 and ink weed (Phytolacca octandra L.) fruits. (Sphecotheres viridis Vieillot) Silvereyes (Zosterops lateralis Latham) disperse Olive-backed oriole 11 32 (Oriolus sagittatus Latham) the greatest number of weed species (including lan- Crimson rosella 11 44 tana) as well as 23 native species at risk from lantana, (Platycercus elegans Gmelin) while regent bowerbirds (Sericulus chrysocephalus Regent bowerbird 11 73 Lewin) are responsible for dispersing 73 native spe- cies at risk from lantana invasion, as well as 11 weed species (Table 2). Birds D ispe P ed ro rses seed DISCUSSION se vides frui ts/seeds Lantana poses a significant threat to native plants in perses frui s ts/s Di ides Australia. Whilst seeds of many of these species are v eeds ro P dispersed by birds, these vectors are also known to Impact on disperse lantana and other weeds. This relationship Native plants Invasive plants between birds and weeds has provided a significant insight into the role birds can play in weed manage- Figure 1. The role of birds in weed invasions, native ment, some of which we have not clearly understood species declines and restoration. 31 Sixteenth Australian Weeds Conference Compounding the problem is that as native plant Crome, F., Isaacs, J. and Moore, L. (1994). The utility species decline following lantana invasion, native to birds and mammals of remnant riparian veg- birds may in turn consume more lantana fruits, thus etation and associated windbreaks in the tropical increasing dispersal and invasion and decreasing the Queensland uplands. Pacific Conservation Biol- dispersal of native plants. ogy 1, 328-43. This bird-weed interaction has profound implica- DECC (2007). Managing the impact of lantana tions for revegetation and the long-term restoration on biodiversity: a national challenge. DECC, of invaded sites, as it will be difficult to stop further Hurstville. (Accessed online 8/10/07). http://www. dispersal of weeds into these managed sites. A gradual nationalparks.nsw.gov.au/npws.nsf/Content/Lan- and staggered approach to lantana removal has been tana_threat_to_biodiversity.