The role of intense nest predation in the decline of Scarlet Robins and Eastern Yellow Robins in remnant woodland near Armidale, New South Wales

S. J. S. DEBDSI

A study of open-nesting Eastern Yellow Robins australis and Scarlet Robins multicolor, on the New England Tablelands of New South Wales in 2000-02, found Iow breeding success typical of eucalypt woodland . The role of intense nest predation in the loss of birds from woodland fragments was investigated by means of predator-exclusion cages at robin nests, culling of Pied Strepera graculina, and monitoring of fledging and recruitment in the robins. Nest-cages significantly improved nest success (86% vs 20%) and fledging rate (1.6 vs 0.3 fledglings per attempt) for both robin species combined (n = 7 caged, 20 uncaged). For both robin species combined, culling of currawongs produced a twofold difference in nest success (33% vs 14%), a higher fledging rate (0.5 vs 0.3 per attempt), and a five-day difference in mean nest survival (18 vs 13 days) (n = 62 nests), although sample sizes for nests in the cull treatment (n = 18) were small and nest predation continued. Although the robin breeding population had not increased one year after the cull, the pool of Yellow Robin recruits in 2001-03, after enhanced fledging success, produced two emigrants to a patch where Yellow Robins had become extinct. Management to assist the conservation of open-nesting woodland birds should address control of currawongs. Key words: Woodland birds, Habitat fragmentation, Nest predation, Predator exclusion, Predator removal.

INTRODUCTION predation occurs across the rural landscape generally, including the woodland interior, by INCREASED nest predation in fragmented and predators that occur in woodland rather than degraded eucalypt woodlands was one of the edge or open country. specific mechanisms hypothesized by Ford et al. (2001) for the loss and decline of species The Pied Strepera graculina is a from woodland in southern . Many nest predator whose population has increased in open-nesting small , including robins eastern Australia, probably owing to the inclusion (Petroicidae), flycatchers (Dicruridae), whistlers of exotic fruits and other novel (human- (Pachycephalidae) and honeyeaters (Meliphagidae), provided) foods in its diet, its wide dispersal of experience poor nesting success in remnant invasive plants via regurgitated seeds, and its vegetation in the region, with young fledging transition to an urban wintering and breeding from about 20% of nests (reviewedby Ford etal. bird (Bass 1989, 1990, 1995; Major et al. 1996; 2001; Higgins et al. 2001; Fitri and Ford 2003; Wood 1998, 2000; Rose 1999; Bayly and Blum- Higgins and Peter 2003; Debus and Lollback stein 2001; Fulton and Ford 2001 b). For robins 2005). Poor nest success and high rates of nest and other woodland passerines predation is the predation are characteristic of the life histories main cause of nest failure, and the currawong of small passerines in southeastern Australia is believed to be the main nest predator (Woinarski 1985; Yom-Tov 1987; Robinson (Robinson 1990; Major et al. 1996; Zanette and 1990), but it is unclear whether this feature is J enkins 2000; Ford et al. 2001; Berry 2001, natural or whether nest success has declined in 2002). However, the presumed role of the recent decades with changes in land use. currawong in reducing bird populations and causing local declines is controversial (Bayly and Many experiments on artificial nests have Blumstein 2001), and has been tested (and tested whether predation differed between proven) only on a seabird nesting on an offshore remnants of different sizes, or at edges versus island, where habitat degradation had also woodland interior; that is, whether predation is exposed nests to predation (Priddel and Carlile linked to fragmentation (Gardner 1998; Taylor 1995). The currawong may now impose and Ford 1998; Major et al. 1999; Matthews et sufficiently high predation on nests of small al. 1999; Zanette and Jenkins 2000; Fulton and woodland birds so that there are too few Ford 2001a; Berry 2002; Piper et al. 2002; Zanette 2002). These results have been fledglings to replace adult mortality and allow emigration among remnants. equivocal, with at best modest evidence for higher predation on edges or in smaller Although culling of currawongs led to a remnants. Instead, it appears that high nest significant decline in the predation rate on

'Division of Zoology. University of New England. Armidale, New South Wales, Australia 2351. PACIFIC CONSERVATION BIOLOGY Vo!. 12: 279-87. Surrey Beatty & Sons. . 2006. 280 PACIFIC CONSERVATION BIOLOGY

artificial nests with real (Fulton and Ford 2006). In 2000-2002 the reserve supported 200 la), there was still a high predation rate on 10-12 pairs of Scarlet Robins, distributed fairly eggs, suggesting that other predators (as well as evenly throughout, and 8-10 pairs of Yellow remaining currawongs on the cull site) were also Robins, distributed patchily though with similar involved. There is a need for controlled numbers in the northern and southern halves of experimental studies to elucidate what role the the reserve (Debus 2006). currawong plays in reducing fledging rates and Normally, the reserve supports 10-12 breeding recruitment, and consequent decline of pairs of currawongs, distributed fairly evenly woodland passerines (Bayly and Blumstein 2001; throughout (pers. obs.; Fulton and Ford 2001a). Fulton and Ford 2001a). Currawongs appear to Other known or suspected nest predators be most predatory during their own breeding included at least five adult pairs of Grey season (September-December), often taking and Cracticus torquatus, kookaburras caching vertebrate prey for feeding to their Dacelo, honeyeaters, Grey -thrush mates or young (Cooper and Cooper 1981; Colluricincla harmonica, Olive-backed Oriole Prawiradilaga 1994; Wood 1998, 2000). Griolus sagittatus, Black-faced -shrike The Petroica multicolor and Coracina novaehollandiae, three corvid species, Eopsaltria australis and Common Brushtail Possums Trichosurus (hereafter Yellow Robin) build open, cup-shaped vulpecula (Fulton and Ford 2001a; Debus 2006). nests in the tree and shrub canopy of temperate woodlands. They have low nest success (10-40%: Monitoring of robin nests Marchant 1984, 1985; Robinson 1990; Debus 2006) and the Scarlet Robin is declining in most Field procedures and baseline data for 2000, of its range, although the evidence for a decline a control year, are detailed elsewhere; robins in Yellow Robins is contradictory, with increases were colour-banded in all years (Debus 2006). in some regions but declines in others, including Protected and unprotected robin nests in both New England (Barrett and Silcocks 2002; Barrett years of the experimental study (2001-02) were et al. 2003). An important question is whether monitored daily or almost so, until success or currawongs limit nest success, recruitment and failure. Particularly in 2002, nests were monitored hence the breeding population of robins in from as close as possible to initiation (95% remnants. The aim of this study was to found at building, laying or start of incubation), and only those nests in which laying was determine whether protection from, and culling confirmed were included in calculations of nest of, currawongs leads to reduced nest predation, and in particular to more juvenile robins success. Results from nests found in all years of reaching independence, and whether these the study (2000-02) were included in offspring join the local breeding population and assessments of nest failure and post-fledging hence increase the subpopulation. progress. The present study addressed the currawong Caging of nests nest-predation hypothesis by protecting nests Cages were deployed in the 2001 robin from predators by means of (a) predator- exclusion cages around some nests of Scarlet breeding season. Cages were constructed of Robins and Yellow Robins in 2001 and (b) lengths of plastic garden trellis mesh 91 cm removing the currawongs from half of a 270 ha deep, of mesh size 5 X 5 cm (permitting free passage of robins, but excluding birds of Grey woodland patch in spring 2002, and monitoring Shrike-thrush size and larger). Brown mesh was fledging success at protected and unprotected used for nests on dead branches, and olive- robin nests and recruitment of juveniles into the green for nests among live foliage. Cages were breeding population. constructed as cylinders with the nest at the centre, and the top and bottom cut, folded in STUDY AREA AND METHODS and secured by green garden-ties. The radius (27 cm), and hence circumference required Study site (1.7 m), of the cage was calculated to place the The study site was Imbota Nature Reserve nest beyond the reach of a currawong pushing (formerly Eastwood State Forest), 10 km south- its head through the mesh (from specimens: head-bill = 12 cm, doubled for maximal neck east of Armidale (30030'S, 151040'E) on the New extension = 24 cm). Nests caged were at least England Tablelands of New South Wales. This 1.5 m above the ground, but limited to those woodland patch of about 270 ha, including within reach of a 2 m stepladder. contiguous intact woodland on private land, has been described by Ford et al. (1986), NPWS Acceptance of cages by parent robins was (2002) and Hunter (2003), with details confirmed at the nestling stage, before summarized by Debus (2006). The study period extending the procedure to nests with eggs. The culminated in the dry year of 2002 (see Debus latter were caged only after incubation was fully DEBUS: INTENSE NEST PREDATION OF SCARLET ROBINS AND EASTERN YELLOW ROBINS 281 established, several days after the clutch was simulations (to check on the validity of X2 tests complete. Seven cages were installed: one where sample sizes or expected values are small; around a Scarlet Robin nest, and six around Zaykin and Pudovkin 1993). Similarly, success of Yellow Robin nests (excluding one trial cage, that robin nests in the currawong cull area versus the failed, for each species, after which the radius non-cull area was analysed by means of X2 and circumference were increased to the contingency tables (cull!non-cull vs success/fail), dimensions given). Most Scarlet Robin nests the outcomes confirmed by Monte Carlo were impractical to cage, being high and often simulations. For logistical and administrative on precarious dead branches (Debus 2006). reasons the cull could not be initiated at the start of the robin nesting season, so results were Culling of currawongs pooled for all unprotected nests: the non-cull area (entire breeding season) and the cull area The southern half of 1mbota was chosen for before the cull started (Appendix 1). Success was culling of currawongs, being the opposite half defined as the proportion of nesting attempts from which nesting currawongs were culled by (clutches laid) that resulted in fledged young. Fulton and Ford (2001a) in 1999. The location Mean duration of robin nest survival, from of resident, nest-building pairs of currawongs clutch initiation, in cull versus non-cull areas was was established throughout 1mbota in August- October 2002. The northern half of Imbota had analysed by means of a generalised linear model using ANOVA to test for interactions between been fully reoccupied by new pairs since the species and treatments. For Mayfield estimates previous cull. of nest survival (Mayfield 1975; Johnson 1979), Currawong nesting was prevented in south standard errors and 95% confidence intervals Imbota for the duration of the currawong (2 X SE) were calculated to ascertain statistical breeding season, and the latter two-thirds of the significance at P = 0.05 for categories being breeding season, in 2002. Five adult compared (caged vs uncaged in 2001, cull vs pairs of currawongs were culled in the third non-cull in 2002, and the three-year baseline week of October, before they laid eggs, and two 2000-02 vs caged or cull). days before the first incubating currawong was seen in the northern half. Immediate RESULTS replacement currawongs (n = 5) were culled in the following week, then a further four in Baseline and control data November and two in December, as soon as they were detected. Regular (almost daily or initially Only 33% and 9% of unmanipulated nests of YellowRobins and Scarlet Robins were successful, twice daily) patrols were maintained for currawongs until the last robin fledglings were over three breeding seasons 2000-02 inclusive fully grown in early February 2003. (Yellow Robin: 5/11, 3/8, 5/21 nests; Scarlet Robin: 2/10, 1/12, 1123 nests, in 2000, 2001 and Statistical analysis 2002 respectively). Mayfield-adjusted baseline values for probability of nest survival over the Nest success from caged versus uncaged nests three years were 0.24 and 0.08 for each species was analysed by means of two-by-two X2 (Table 1). The overall fledging rate was 0.6 and contingency tables (caged/uncaged vs success/ 0.1 young per attempt for Yellow and Scarlet fail), the outcomes confirmed by Monte Carlo Robins respectively. Predation (80%) was the

Table 1. Mayfield probability of nest survival (Mayfield 1975; Johnson 1979) for Yellow Robins and Scarlet Robins. Baseline data (2000-02) and predator treatments: nest cages 2001, currawong cull 2002. 95% Cl = 95% confidence interval (:1:2 x SE); *p < 0.05 where 95% Cl for compared treatments do not overlap.

Species/treatment Nest survival SE 95% Cl Yellow Robin: Baseline, all years 0.24 0.011 0.22-0.26 2001 uncaged 0.24 0.034 0.17-0.31 2001 caged 0.75 0.010 0.73-0.77* 2002 non-cull 0.19 0.015 0.16-0.22 2002 predator cull 0.37 0.014 0.34-0.40* Scarlet Robin: Baseline, all years 0.08 0.016 0.05-0.11 2002 non-cull 0.07 0.017 0.04-0.10 2002 predator cull 0.22 0.018 0.18-0.26* Both species combined: 2001 un caged 0.18 0.020 0.14-0.22 2001 caged 0.82 0.007 0.81-0.83* 282 PACIFIC CONSERVATION BIOLOGY main cause of nest failure, and currawongs were Table 2. Nest success and number of fledglings ITom caged and among the nest predators observed. Predation uncaged Yellow Robin and Scarlet Robin nests 2001. continued post-fledging, with about 30% of No. of No. successful No. failed juveniles disappearing during the dependence Species nests (No. of young) (%) period (Debus 2006). Yellow Robin: caged 6 5 (10) I (17) Acceptanceof nest-cages uncaged 8 3 (5) 5 (63) Scarlet Robin: Yellow Robins and Scarlet Robins immediately caged I I (1+)A 0 (0) accepted cages installed around nests with chicks, uncaged 12 I (1) 11 (92) returning to brood as soon as the observers had Both species: retreated. Similarly, they immediately accepted caged 7 6 (11) I (14) uncaged 20 4 (6) 16 (80) cages installed around nests with eggs once incubation was established for several days. ABrood of three young reached fledging age; only one seen There were no cases of nest desertion out of nest. attributable to installation of cages. However, there was one case of apparently human-induced Predator removal nest desertion before installation of a cage, For Yellow Robins, nest success was 40% in the towards completion of the clutch or at the start cull treatment versus 24% for nests not subject of incubation. During a pre-installation check, to currawong control in 2002; for Scarlet Robins, the sitting female Yellow Robin was invisible on 25% versus 4%. Culling of currawongs did not the low (1.5 m) nest and was inadvertently significantly increase nest success for Yellow flushed from a clutch of two eggs. She did not Robins (X21= 0.86,P = 0.392)or ScarletRobins return, despite immediate retreat of the observer. (X2J = 2.90, P = 0.15), although the sample size for successful Scarlet Robin nests was small Predator exclusion (Table 3). For both species combined, the cull Nest success for Yellow Robins in 200 I was treatment produced a twofold difference in nest 83% for caged versus 38% for uncaged nests, success that was almost significant (33% vs 14% producing 1.7 and 0.6 fledglings per attempt nest success; X2J = 3.18, P = 0.10), with small respectively (Table 2); in 2001 the only brood of sample sizes in the cull treatment. three fledglings came from a caged nest (broods The Mayfield-adjusted estimates of nest usually 1-2; n = 8 in 2001). The difference in survival also reveal a positive effect from success between caged and uncaged nests of predator control: the currawong cull increased Yellow Robins in 2001 was not significant, success twofold for Yellow Robins and threefold though sample size was small for caged nests for Scarlet Robins within 2002, and by similar (X2[ = 2.94, P = 0.124). The success rate of amounts above the three-year baseline, an effect caged nests was significantly higher than that for that was significant (P < 0.05; Table 1). unprotected nests over the three baseline years, 2000-02 (33%; X2J = 5.66, P = .0.017). The The fledging rate was higher in the cull area single caged Scarlet Robin nest produced at least for Yellow Robins (0.60 vs 0.48 fledglings per one fledgling from a brood of three that reached attempt respectively), Scarlet Robins (0.38 vs fledging age. 0.09 fledglings) and both species combined (0.50 vs 0.27 fledglings, Table 3). The difference was Predator-exclusion cages significantly increased particularly evident for Scarlet Robins: 23 nest nest success for both robin species combined in attempts in the non-cull area produced one 2001 (86% vs 20%; X2J = 9.60, P = 0.001), brood of two fledglings; eight attempts in the producing 1.6 and 0.3 fledglings per attempt respectively. This result was influenced by the small number of Scarlet Robin nests that could Table 3. Nest success and number of fledglings from Yellow Robin and Scarlet Robin nests with and without be caged, the large number that could not, and currawongs culled 2002. the high failure rate for uncaged nests of this species (Table 2). The success rate of No. of No. successful No. failed nests unprotected nests over three years (20%) was Species (No. of young) (%) also significantly lower than that of caged nests Yellow Robin: (X2( = 14.90,P = 0.000). cull 10 4 (6) 6 (60) non-cull 21 5 (10) 16 (76) The Mayfield-adjusted estimates of nest Scarlet Robin: survival reveal a clear benefit from predator cull 8 2 (3) 6 (75) exclusion: nest-cages increased success threefold non-cull 23 1 (2) 22 (96) for Yellow Robins al1d fourfold for both species Both species: cull 18 6 (9) 12 (67) combined, an effect that was significant non-cull 44 (P < 0.05; Table 1). 6 (12) 38 (86) DEBUS: INTENSE NEST PREDATION OF SCARLET ROBINS AND EASTERN YELLOW ROBINS 283

cull area produced three fledglings (BIl, B/2). remained in Imbota. Of three Scarlet Robins For Yellow Robins, brood sizes at fledging were fledged from two of eight nests in the currawong similar: 1-3 young per brood (n = 10 broods) in cull area in 2002, two reached independence the non-cull area (B/l x 1, B/2 x 3, B/3 x 1; and one of these remained in Imbota. Thus, mean = 2.0), and 1-2 (n = 4 broods) in the cull potential recruits from enhanced fledging area (BIl X 2, B/2 x 2; mean = 1.5). success in 2002 served only to provide dispersers, and to partially replace populations Yellow Robin nests survived 2-3 days longer that had declined from the 2000-01 baseline. than Scarlet Robin nests on average (Table 4), a non-significant difference (mean 16 and 13 d; DISCUSSION Fl.57 = 0.76, P = 0.388). There was no interaction between species and treatments (Fl,57= 0.01, P = 0.925). For both species combined, the Success of unmanipulated nests mean duration of nest survival was five' days Eastern Yellow Robins and Scarlet Robins longer in the cull area than the non-cull area (18 experience low nesting success at Imbota, with vs 13 d, Table 4): a difference that approached failures caused mostly by predators, including significance (Fl.57= 3.14,P = 0.078),withsmall the (Debus 2006). This result sample sizes in the cull treatment. is consistent with other studies of nest success, fledging success and the causes of nest failure Table 4. Duration of survival (days) for Yellow Robin and in robins of southeastern Australian temperate Scarlet Robin nests with and without currawongs woodlands (see Marchant 1984, 1985; Robinson culled in 2002, from initiation of clutch (nests 1990; Zanette et al. 2000). However, nest success excluded where initiation date uncertain). and productivity can be much higher, and Species No. nests Range Mean SD predation rates much lower, in southwestern Yellow Robin: Australian forest (Russellet al. 2004) from which, cull 9 4-30 19.2 10.6 notably, the Pied Currawong is absent although non-cull 18 2-28 14.3 9.6 most of the other avian nest predators, including Scarlet Robin: the Strepera versicolor, are cull 8 2-29 17.0 12.0 present (Barrett et al. 2003). non-cull 23 2-27 11.6 9.2 Both species: cull 17 2-30 18.2 11.0 Protected nests non-cull 41 2-28 12.8 9.3 Results from caged nests, most of which were successful, confirm that predation is the major Recruitment cause of nest failure. Robins also experienced Of 10 Yellow Robins fledged from six caged higher nest survival rates in the area where nests in 2001, seven reached independence; one currawongs had been culled, suggesting that of these dispersed to another patch. This result currawongs are a major nest predator. This compares with 14 fledglings and 12 reaching result accords with the artificial nest experiments independence, from 20 uncaged nests in .2000 of Fulton and Ford (2001a). However, at Imbota and 2001. Thus, protection from predators nest predation continued after the removal of probably led to three or four additional, cur.rawongs, probably because of the wide range potential recruits. Two birds from caged nests of other nest predators in the cull area. recruited to an increased breeding population in The low sample size of caged and uncaged spring 2002, but later in 2002 the robin Yellow Robin nests in 2001, and cull versus non- population dropped to below the number of cull nests in 2002, conferred low statistical pairs or groups present in 2001. Hence, the power. Adopting the precautionary principle, it extra fledglings from caged nests produced no is likely that a significant effect occurred but was sustained increase in the breeding population. not detected. A similar caution applies to the Of 10 juvenile Yellow Robins fledged from 21 unbalanced data set, with small sample size of nests in the cull area, for duration of nest nests in the non-cull area in 2002, eight reached survival (Table 4). That is, although large effects independence and at least five of these remained were not evident, small or medium effects are in Imbota. Of six Yellow Robins fledged from 10 nests in the currawong cull area in 2002, three plausible and indeed the Mayfield estimates reached independence and two of these detected significant effects (Table 1). remained in Imbota (one after dispersing to Several factors may have confounded the another patch and returning). This outcome results of the currawong cull. First, within-patch produced perhaps only one more recruit than variation: two Yellow Robin territories in the would be expected without. control of non-cull area consistently had high breeding currawongs. Of two juvenile Scarlet Robins success over the three years 2000-02, whereas fledged from one of 23 non-cull nests in 2002, the other territories in Imbota had lower and at independence one disappeared from and one variable success, perhaps related to habitat 284 PACIFIC CONSERVATION BIOLOGY features. These two productive robin groups were determine the carrying capacity of a patch, but in currawong territories, and were not in the nest predation may limit recruitment and keep part of Imbota that escaped predation in 1999 local populations below carrying capacity, by (cf. Fulton and Ford 2001a). These exceptional limiting emigration. A lack of dispersers may territories also had an active Little Eagle increase the extinction probability for small Hieraaetus morphnoides nest on their mutual populations. Thus, currawongs may have a role boundary; the eagles defended the area against in the population dynamics of robins at the predators such as corvids (pers. obs.). Third, landscape scale, by influencing whether patches removal of resident currawongs in the like Imbota can sustain or rescue other patches, experimental part of Imbota may have allowed and also whether smaller patches can maintain currawong pairs from the north to extend their their populations despite limited immigration. foraging ranges, and floaters to invade. The ongoing cull may also have lessened predation Management implications pressure in the northern non-cull area. Nest-cages could be trialled on other declining The results at Imbota do not demonstrate such passerines that build low nests, as some other clear-cut benefits from predator control as the species also accept nest-cages (fairy-wrens Malurus results on nesting Petroicarobins in New Zealand and small honeyeaters:Franklin et al. 1995; Van (Armstrong et al. 2000; Powlesland et al. 2000; Bael and Pruett-Jones 2000). However, some Etheridge and Powlesland 2001). However, in species may be less tolerant than robins, and New Zealand the main predators are-introduced ideally sites should have appropdate cover to mammals rather than native avian predators; ensure survival of fledglings. Cages are ethically nest-robbing large birds (butcherbirds, currawongs preferable to culling of predators, but are or corvids) are absent from New Zealand. The labour- intensive. results for Imbota are nevertheless consistent This study revealed that culling of Pied with those of Zanette and Jenkins (2000) on Currawongs can lead to a twofold or greater Yellow Robins: some fragments had high rates increase in nest success. These results provide of nest predation and were demographic sinks some support for the control of currawongs. (i.e., recruitment was less than adult mortality), Given the currawong's abundance and the loss of whereas others had lower rates of nest predation some of its main predators (e.g., large owls) from and were potential sources (i.e., recruitment at woodland fragments, control of currawongs least compensated for adult mortality). seems a reasonable option for landholders wishing to protect passerine nests. Culled birds appear Recruitment to be replaced rapidly, so that removal may need Increased success of individual nests need not to be repeated within and between years. lead to more recruits or to increased population In such cases of uncertainty, where currawongs size, at least partly because these aspects are also may not have a large effect but probably have a influenced by the number of nesting attempts small or medium effect, adopting the precaution- (Nagy and Holmes 2004). Predation on nestlings ary principle means that a precautionary measure and fledglings may be compensatory rather than (i.e., control of currrawongs) isjustified. The issue additive forms of mortality (Newton 1998, of currawongs has parallels with the controversy 2000), and the evidence for impact on over fox predation on native mammals. The populations, by nest predators such as corvids, proponents of fox control were criticised on is equivocal (Stoate and Thomson 1998). statistical grounds, but precautionary measures were vindicated by long-term study (cf. Friend Reduced nest predation, and enhanced 1990 and Kinnear et al. 2002 vs Hone 1994 and recruitment to independence, did not result in Bomford et al. 1995). an increase in the robin breeding population at Imbota. At best it resulted in partial replacement There is likely to be an interaction between in 2003 of pairs lost during 2002. However, the nest predation and habitat or other aspects of extra recruits in 2001 and 2002 may have resource availability for small birds (Weidinger prevented a more serious decline of the robin 2002; Zanette et al. 2003; Nagy and Holmes populations during 2002-03. Furthermore, the 2004; Debus, unpubl. data). Therefore, manage- pool of Yellow Robin recruits in 2001-03, after ment should include enhancement of habitat enhanced fledging success from the nest-cages quality (e.g., plantings of an indigenous shrub and currawong cull, produced two dispersers to layer) in remnant woodland. Enhancement of another patch, where Yellow Robins had become resources and control of predators may have a extinct but to which they had been reintroduced synergistic benefit greater than the sum of either in 2001 (Debus and Ford, unpubl. data). alone (Zanette et al. 2003). Habitat, nest predation and dispersal probably Control actions should also aim to reduce all play a role in the decline of woodland birds. resources in the matrix that sustain nest Habitat quality and food supply may ultimately predators in fragments (Chalfoun et al. 2002). DEBUS: INTENSE NEST PREDATION OF SCARLET ROBINS AND EASTERN YELLOW ROBINS 285

Management, preferably through education and permitted field-work on their land. Dr Stuart extension, should therefore be directed towards (Zoology, UNE) ran the statistical tests. eradication of introduced berry-bearing plants The project was aided financially by the Stuart (which provide abundant winter food sources for Leslie Bird Research Awards (Birds Australia), currawongs) from urban, rural and bushland the NSW Field Ornithologists Club research areas, and their replacement with locally grants, the Joyce W. Vickery Scientific Research indigenous trees and shrubs. Fund (Linnean Society of NSW) and the NSW National Parks and Wildlife Service (Western ACKNOWLEDGEMENTS Directorate, Dubbo), and in kind (with gratis mist-nets and colour-bands) by the Australian This study formed part of a PhD project, Bird Study Association's Fund for Avian supported by an Australian Postgraduate Award Research. The research was conducted under (administered by UNE) and by the Division of UNE Ethics permits AEC 2000/0081, 011 Zoology, UNE. Ben Boland, Will Buchanan, 042 and 02/074, with authorisation from NSW Lachlan Debus, Sandy Hamdorf, Annette and NPWS and the Australian Bird and Bat Banding Matt Harrison, Andrew Ley, Greg Lollback, Jim Scheme. Hugh Ford supervised the project, and Palmer, Kihoko Tokue and Paul Webber provided he, Doug Armstrong and Shelley Hinsley field assistance. Andrew Taylor and Ken Pines' critically reviewed the relevant thesis chapter. I (NSW National Parks and Wildlife Service, thank Hugh Ford, Harry Recher and referees Armidale) and Steve Tremont assisted with Ted Davis and Mike Calver for comments on a logistics of the currawong cull. Neighbours of draft. Imbota, the Burton and Moffitt families,

APPENDIX 1

Data fOTYellow Robin and ScaTlet Robin nests in nOTth Imbota (currawongs not culled) and south Imbota (currawongs culled) in 2002, befoTe and afteT the cull took place. N = No. of nests in each category.

Site/peTiod Yellow ScaTlet Both NOTth: Pre-cull succeed 2 1 3 fail 3 4 7 Post-cull succeed 2 0 2 fail 4 4 8 South: Pre-cull Succeed 1 0 1 Fail 9 14 23 Post-cull Succeed 4 2 6 Fail 6 6 12

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Fourth Biennial AUSTRALASIAN ORNITHOLOGICAL CONFERENCE Call for Papers and Expressions of Interest The Fourth Biennial AustralasianOrnithologicalConferencewill be held in Perth, Western Australia on 3rd to 5th of December 2007. This conference provides a regular forum for the exchange of information and ideas between avian researchers and conservationists throughout the Australasianregion. The venue will be the University of WesternAustralia, and the Western Australian group of Birds Australia (RAOU) will host the conference. A post-conference field excursion will be available. An Invitation You are invited to express your interest in attending this conference, and presenting a paper by visiting www.birdswa.com.auJaoc2007 or link through www.birdswa.com.au or www.birdsaustralia.com.au or by writing to the conference co-ordinator: S. MATHER Birds AustraliaWesternAustralia 167 Perry Lakes Drive, Floreat, Western Australia, Australia 6014 Email: [email protected] Telephone: 61 (0)8 9389 6416