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Australian Field Ornithology 2021, 38, 19–28 http://dx.doi.org/10.20938/afo38019028

Breeding diets of the Little morphnoides and Wedge-tailed Eagle Aquila audax in the Australian Capital Territory in 2011–2019

S.J.S. Debus1*, Jerry Olsen2**, Susan Trost3 and Esteban Fuentes4

1Zoology, University of New England, Armidale NSW 2351, 2Institute for Applied Ecology, University of , ACT 2601, Australia 344 Wybalena Grove, Cook ACT 2614, Australia 4Instituto Tecnológico y de Estudios Superiores de Monterrey Campus León, Av. Eugenio Garza Sada S/N, León, Gto. 37190, México *Corresponding author: Email: [email protected] **Deceased

Abstract. The diets of the Little Eagle Hieraaetus morphnoides and Wedge-tailed Eagle Aquila audax breeding sympatrically in the Australian Capital Territory during 2011–2019 were compared by analysis of pellets and prey remains (six Little Eagle territories and 13 Wedge-tailed Eagle territories; 69 and 49 collections for a total of 232 and 256 prey items, respectively). Little took 33% (29% European Rabbits Oryctolagus cuniculus), 44% , 6% and 17% by number, and 65% mammals (62% Rabbits), 27% birds, 8% reptiles and <1% insects by biomass. Wedge-tailed Eagles took 59% mammals (23% Rabbits and 19% macropods), 38% birds, 1% reptiles, <1% fish and 1% insects by number, and 89% mammals (20% Rabbits, 38% macropods), 10% birds, and <1% reptiles, fish and insects by biomass. Indices of dietary diversity (Shannon Index and Standardised Food Niche Breadth) were 2.57 vs 3.07 and 0.19 vs 0.24, respectively; Geometric Mean Prey Weights (GMPW) were 164 vs 1392 g, but discounting a biased sample of insects in many pellets from two fledglings, Little Eagle GMPW was more like 340 g. Dietary proportions and some metrics for both appear to have changed little since the preceding decade, although Wedge-tailed Eagle dietary diversity increased slightly and dietary overlap (80%) increased greatly, concomitantly with some pairs of Wedge-tailed Eagles replacing pairs of Little Eagles. Intraguild predation occurred, including Wedge-tailed Eagle predation on Little Eagles.

Introduction Here we compare the diets of the two eagle species in contiguous territories within the ACT over the period 2011–2019, to further investigate their diets in sympatry Olsen & Fuentes (2004, 2005) first signalled a decline and any changes over time. The context for the study since the 1990s in breeding Little Eagles Hieraaetus is controversy over the Little Eagle’s population and morphnoides in the Australian Capital Territory (ACT). in the ACT, and the likelihood that The Little Eagle is now considered threatened in interactions with the Wedge-tailed Eagle as well as urban some southern Australian jurisdictions, being listed as sprawl, and perhaps secondary poisoning from pindone Vulnerable in (NSW), the ACT, Victoria baiting to reduce Rabbit numbers, may be adversely and South Australia in relevant legislation. Further affecting the Little Eagle (e.g. Olsen 2018, 2019). knowledge of its ecology and requirements, particularly in areas affected by human impacts (e.g. urban expansion in Canberra, ACT), will assist in its conservation and Study area and methods management. For instance, significant gains have been made on understanding its breeding- and - The general study area of peri-urban Canberra and site requirements (Larkin et al. 2020) and the home- surrounding rural ACT has been described in previous range and roosting requirements of a fledgling (Olsen papers, i.e. eucalypt-dominated open (in Canberra et al. 2017). Nature Parks), woodland, open woodland and tree-dotted pasture, with River She-oak Casuarina cunninghamiana The breeding diets of the Little Eagle and Wedge-tailed gallery forest on the Molonglo River (e.g. Olsen et al. Eagle Aquila audax in various parts of Australia are now 2006a,b, 2010, 2013a; Fuentes et al. 2007). Dietary well known, especially for the latter species, whose diet characteristics of breeding eagles (active to has been studied comprehensively in every State and dependent fledglings) were determined by analysis of prey Territory (reviewed by Marchant & Higgins 1993; Debus remains and pellets collected from under nests and roosts. 2017). Their diets have been compared quantitatively, Sampled were six Little Eagle territories from January 2012 using food-niche metrics, for contiguous territories in the to November 2018 (Table 1), and 13 Wedge-tailed Eagle ACT in 2002–2008 and again in 2008–2010, with a small territories from September 2011 to December 2019 (69 and change in dietary proportions as the number of European 49 collections for a total of 232 and 256 prey items, over Rabbits Oryctolagus cuniculus increased (Olsen et al. 15 and 33 nest-years, respectively). At least six (possibly 2010, 2013a). Rae et al. (2018, 2019, 2020) presented seven) of these Wedge-tailed Eagle territories were dietary data for the Little Eagle in the ACT and adjoining individually contiguous with each of the six concurrently NSW (within 30 km of the ACT), but not separately for the active Little Eagle territories or home-ranges, another ACT (i.e. peri-urban Canberra) and rural NSW although two overlapped former but vacated Little Eagle nesting some dietary differences may exist between the two areas. territories, and one was in an area inhabited by a pair of 20 Australian Field Ornithology S.J.S Debus et al.

Table 1. Number of pellets and orts collected per Little example, one Rabbit or macropod might be represented Eagle territory in the ACT, 2012–2018. in about three pellets containing that species, if there were few or no orts in that sample for confirmation. The dates of Territory No. pellets No. orts collection within and between breeding seasons, especially 1 18 5 when separated by weeks to ≥1 month within a season, 2 92a 39 also helped to refine estimates of MNI in pellets (e.g. 3 54 38 new pellets or orts after a substantial interval of ≥1week were assumed to represent new prey individuals). A given 4 6 4 vertebrate prey species that appeared in several pellets 5 1 3 over ≥2 consecutive days was assumed to represent one 6 7 15 individual unless orts indicated otherwise. In most cases, Total 178 104 other than some orts, it was not possible to assign an age- aThirty-eight of these were collected from under the roosts of two dependent juveniles class to the larger species consumed (e.g. only that were foraging on insects. fur or hair in pellets), so we relied on wastage factors and other considerations (above) for biomass consumed. In Little Eagles not known to breed during the study. The the case of Little Eagles, that meant 740 g (upper limit) remainder were in the surrounding ACT where occupied less 33% wastage = MNI × 496 g as an approximation of Little Eagle territories were not known or sampled but, Rabbit biomass consumed (cf. adult and juvenile Rabbit except for the Gudgenby site, probably occurred. To avoid weights of 1500 and 500 g, and twice as many juveniles as disturbance and undue attention to the nests, locations or adults taken, in 2008–2010: Olsen et al. 2013a). a map are not provided here. We stress that most prey items were from pellets, Pellets and prey remains (orts) were analysed and Rabbit orts were not aged, and consequently MNI for both identified by Georgeanna Story (www.scatsabout.com.au). eagle species, and Rabbit weights for the Little Eagle, The methods and rationale for identifying prey items, are estimates. Our approach was to replicate as closely calculating the minimum number of prey individuals (MNI) as possible A.B. Rose’s dietary analyses in the two earlier and their adjusted biomasses, and statistically treating ACT studies, in order to compare the later (G. Story) the data, are described elsewhere, based on overseas analysis, i.e. maintain consistency in methods across the recommendations on MNI from multiple sources (pellets, three time periods. Because pellets or orts alone may not orts and observations pooled per site per collection fully represent the diet (see Olsen et al. 2010), we also event: see Olsen et al. 2010). Adjusted biomass of quantified and compared the percentage occurrence of prey (consumed) takes into account wastage factors of prey classes in total pellets and the total number of orts different-sized prey, and the maximum amount of usable per prey class against our estimated prey MNI for each tissue the respective eagles can carry (see Olsen et al. eagle species. 2010 for explanation and references). That is, for dietary The dietary metrics Geometric Mean Prey Weight biomass calculations on large mammalian prey >10 kg, we (GMPW), Shannon Diversity Index, Standardised Food used an upper limit of consumed tissue for Wedge-tailed Niche Breadth (SFNB), and Pianka Index for dietary Eagles of 3800 g, based on the maximum usable biomass overlap were calculated as in previous papers (Olsen et that they can carry to the nest; and for Little Eagle biomass al. 2006a,b, 2010, 2013a,b). The Shannon Index (ranging calculations on large prey, we used an upper limit of upwards from 1 = lowest diversity) reflects prey species tissue consumed at the nest of 740 g, based on estimates richness, SFNB values (between 0 and 1) reflect little (0) in Marchant & Higgins (1993) of what this species can to high (1) dietary evenness, and the Pianka Index values bring to the nest. Wastage factors applied were: 33% for (between 0 and 1) reflect no overlap (0) to complete overlap mammalian prey 0.3–10 kg; 17% for mammals 75–300 g; (1). Prey weights were taken from Olsen et al. (2006a,b, 20% for birds and reptiles >300 g, 12% for prey 75–300 g, 2013a) and Fuentes et al. (2007) in the first instance, for and 9% for prey <75 g. consistency across eagle studies; otherwise from related We estimated the MNI for some (generally larger) literature. vertebrate species that were represented in several or many pellets but by few or no orts in a given sample. As in previous related studies, we did not assume that one Results pellet represented one prey individual and we accounted for a single prey item appearing in more than one pellet within a sample (e.g. see Olsen et al. 2010; Olsen Diet 2014). According to circumstances, e.g. whether a given sample was collected from a male’s roost and/or a nest Overall, in the present study, Wedge-tailed Eagles took with chick(s), or the roost of a fledgling sometimes with more mammals and fewer birds and reptiles than did a parent, and depending on brood-size, we made some the Little Eagle, both in frequency (% n) and biomass assumptions about MNI in pellets. Large prey (e.g. a (Table 2, Appendices 1–2). However, Rabbits contributed Rabbit or macropod), and other vertebrate prey, is typically relatively more prey biomass for Little Eagles, whereas shared between one or two adults and their nestling(s) Wedge-tailed Eagles consumed many macropods. For the or fledgling(s) (e.g. Debus et al. 2007a,b; our pers. Little Eagle, birds contributed almost half by percentage by obs.), and in a few samples the pellet contents could be number and over one-quarter by biomass (e.g. Figure 1). calibrated against MNI in orts. Large prey may also last Other prey classes contributed low numbers and biomass more than one meal for an adult and its nestling. Taking for both the eagle species (Appendices 1–2), although a conservative approach, we therefore assumed that, for some Little Eagles (mainly juveniles in two summers at Breeding diets of Little Eagle and Wedge-tailed Eagle, ACT, 2011–2019 21

Table 2. Comparative dietary parameters of the Little Eagle and Wedge-tailed Eagle breeding sympatrically in the ACT during three time periods for only the main vertebrate classes of prey taken (i.e. excluding fish and insects): MNI in 2002–2008 (Olsen et al. 2010); 2008–2009 (Olsen et al. 2013a), and estimated MNI in 2011–2019 (this study). GMPW = Geometric Mean Prey Weight, SFNB = Standardised Food Niche Breadth, MNI = mean number of individuals, and n = number.

Parameter Little Eagle Wedge-tailed Eagle 2002–08 2008–09 2012–18 2002–08 2008–09 2011–19 Percentage by number Total mammals 39 52 33 55 65 59 Macropods 1 2 <1 19 19 19 Rabbits 32 50 29 19 34 23 Birds 45 45 44 39 33 38 Reptiles 6 3 6 3 3 1

Percentage by biomass Total mammals 63 73 65 90 93 89 Macropods 5 1 <1 47 35 38 Rabbits 52 72 62 13 20 20 Birds 30 24 27 9 7 10 Reptiles 5 3 8 <1 <1 <1

GMPW (g) 249 337 164a 1298 1650 1392 Shannon Index 2.14 2.28 2.57 3.16 2.75 3.07 SFNB 0.14 0.14 0.19 0.16 0.21 0.24 Pianka Index 0.69 0.46 0.80 aStrongly biased by insects in pellets from dependent juveniles, otherwise GMPW was closer to 340 g one site) took many insects (Table 1). Most of the beetles phase. Similarly, a grasshopper in a Wedge-tailed Eagle taken may have been picked off the nest by the adult pellet was from beneath a fledgling’s roost. The origin of or nestling, although three pellets from the roost of a fish in the diet of the Wedge-tailed Eagle (Appendix 2), dependent juvenile Little Eagle consisted only of beetles, albeit a miniscule component, is uncertain but may have and pellets containing grasshoppers were mainly from been robbed from a Whistling Kite Haliastur sphenurus or beneath a fledgling’s roost, suggesting some opportunistic White-bellied Sea-Eagle Haliaeetus leucogaster (cf. Olsen et al. 2013b), or scavenged. foraging for insects during the post-fledging dependence There was only one site where Rabbits were the main prey of Wedge-tailed Eagles, at Gudgenby in the mountains where Rabbits were in plague proportions in 2015 and their carcasses carpeted the nest. Twenty-three of 24 pellets from 2015 and 2017 contained only Rabbit (one contained Rabbit and kangaroo fur), and remains consisted of eight Rabbit orts (including three skulls), feathers from three birds, a Sheep Ovis aries leg, a kangaroo leg and a skull. The Wedge-tailed Eagle’s diet was more diverse than the Little Eagle’s by both measures (Shannon Index, SFNB), and dietary overlap (Pianka Index) was 80%. However, GMPW for Wedge-tailed Eagles was 8.5 times that for Little Eagles (Table 2). Furthermore, the Little Eagle’s GMPW is heavily influenced by the number of insects taken, itself a sampling bias caused by the number of pellets (38) collected from beneath the nest and roost of a juvenile at one site in December 2012 and again in December 2013 (Table 1). Consequently, insects figure relatively more in pellets collected from beneath this nest and nearby roost-sites than in pellets collected from adults and other sites. If only the typical pellet sources and profile (dietary proportions) are considered, then Little Figure 1. Little Eagle chick with Common Starling prey, Eagle GMPW was closer to 340 g (~25% of Wedge-tailed ACT, 22 November 2014; the nest was subsequently Eagle GMPW, which reflects the eagle species’ fourfold abandoned. Photo: Jerry Olsen & Susan Trost difference in body weight). 22 Australian Field Ornithology S.J.S Debus et al.

It appears that the relative proportions of the major prey categories may have changed little in 2011–19 since the prior ACT studies in 2002–2008 and 2008–2009, with possibly a peak in the proportion of Rabbits taken by both eagle species in 2008–2009, though no change in the proportion of macropods taken by Wedge-tailed Eagles (Table 2). However, the 2008–2009 samples spanned only 2 years, whereas the earlier and present samples were for 6 and 8 years, raising the possibility of bias inherent in a small sample of years. The 2011–2019 data also contain only estimates of prey MNI and Rabbit biomass, and may have contributed (albeit in a minor way) to the slight dietary differences in the different time periods. What is clear and consistent is that in the ACT Wedge-tailed Eagles take relatively more mammals, and Little Eagles take relatively more birds and reptiles, and that mammals (including a variety of large species) are especially important prey biomass for Wedge-tailed Eagles, whereas mammalian Figure 2. Wedge-tailed Eagle with Red prey, ACT, prey for Little Eagles is almost entirely Rabbits. The study 17 October 2016. Photo: Dalice Trost by Fuentes et al. (2007), a subset of that in Olsen et al. (2010), showed that Wedge-tailed Eagles took a higher For Little Eagles, it was not possible to assign an age proportion of macropods in the early 2000s than in past class to any mammalian prey, except for one macropod jaw decades, and that proportion has remained high. which was from a juvenile. One pellet from a different site Dietary diversity (Shannon Index and SFNB) for each contained Eastern Grey Kangaroo Macropus giganteus eagle species was rather similar across the three studies, fur; both items were probably scavenged. The Cat Felis with the possibility of Wedge-tailed Eagles, in particular, catus taken was most likely a juvenile (the ort was a increasing their SFNB over time (Table 2). However, skull, not assigned an age), as a Little Eagle could not GMPW was somewhat variable, even allowing for the subdue or carry an adult Cat. Similarly, Common Brushtail qualifier regarding insects in the Little Eagle’s diet, and Possum Trichosurus vulpecula was consumed (fur in a dietary overlap increased greatly during 2011–2019. The pellet), but orts (fur pluckings, a skull) were not aged; they latter outcome might have been influenced by the high may have been immatures found in exposed positions in proportion of Rabbits in the Gudgenby Wedge-tailed daylight during their dispersal phase (SJSD pers. obs.), Eagle sample, but may also reflect Wedge-tailed Eagles or scavenged. Common Ringtail Possum Pseudocheirus replacing Little Eagles in some territories (see below). peregrinus occurred as fur pluckings at one nest; this nocturnal, drey- or hollow-denning species is within the capture size-range for Little Eagles, but could have been Comparison of dietary sources scavenged (e.g. as road-kill). For the Little Eagle, mammals occurred in 71% of the 178 For the Wedge-tailed Eagle, at least half the macropods pellets (Rabbits in 70%), birds in 56%, reptiles in 4% and consumed were juveniles (Appendix 2), although several insects in 20%. There was fairly close agreement between skulls from older appeared in orts. Wedge-tailed overall % MNI and % n in orts (Table 3), other than insects Eagles are capable of killing large macropods (Fuentes & not represented in orts. Some other items also appeared Olsen 2015). Otherwise, of the Red Vulpes vulpes in pellets but not orts (e.g. Common Ringtail Possum and taken only one among several skulls/jaw(s) was aged as a kangaroo fur), and vice versa (some mammals, e.g. Cat, juvenile, the others either not aged or possibly adult (e.g. as and some birds and reptiles). Mammals might have been in Figure 2). See also Olsen et al. (2020) for a photograph over-represented in the percentage occurrence in pellets of a Wedge-tailed Eagle chasing an adult Fox. Of the because they were larger items shared among an eagle Sheep/lambs eaten, one was aged on the basis of bones family, and birds might have been over-represented in orts as a juvenile and two as adults (i.e. the latter scavenged). by clumps of feathers. Common Wombat Vombatus ursinus appeared only as hair in pellets, so it is uncertain if a juvenile was taken or For Wedge-tailed Eagles, mammals occurred in 94% of an adult was scavenged. the 282 pellets (Rabbits in 64%), birds in 31%, and reptiles and insects in <1%. Again, some items appeared in pellets During the 2019 breeding season of worsening drought but not orts (e.g. Common Wombat, Common Ringtail in south-eastern Australia, Wedge-tailed Eagles continued Possum) and vice versa (e.g. Swamp Wallaby Wallabia with the same prey spectrum (various mammals, birds bicolor, some large birds), and birds might have been over- and reptiles, including some Rabbits) at four sites, and represented in orts. three successful broods were of one, one and two young, respectively. No data could be collected at the known Little Eagle sites after November 2018. However, Little Eagles Interactions between eagle species took some novel foods in 2011–2018 (Common Ringtail Possum and some species) not recorded in the two Remains of the Little Eagle were found at two Wedge- earlier local studies, nor in other Australian studies to that tailed Eagle nests in the present study (Appendix 2), and time (cf. Marchant & Higgins 1993; Debus 2017). at one nest in a study reported earlier (Olsen et al. 2006b), Breeding diets of Little Eagle and Wedge-tailed Eagle, ACT, 2011–2019 23

Table 3. Comparison of three measures of dietary proportions for the Little Eagle and Wedge-tailed Eagle in the ACT in 2011–2019: overall estimated MNI (see Table 2), percentage occurrence (% occ.) in pellets (n = 178 and 282, respectively), and percentage number (% n) in orts only (n = 104 and 177, respectively).

Parameter Little Eagle Wedge-tailed Eagle MNI Pellets Orts MNI Pellets Orts (%) (% occ.) (% n) (%) (% occ.) (% n) Total mammals 33 47 28 59 75 57 Rabbits 29 46 21 23 64 22 Birds 44 37 61 38 25 40 Reptiles 6 3 11 1 <1 2 Fish – – – <1 – 1 Insects 17 13 – 1 <1 – indicating intraguild predation (as also by a Little Eagle other historically active Little Eagle territories (in Mallinson on a Brown Goshawk Accipiter fasciatus, and a Wedge- et al. 1990) have been vacated and are now occupied tailed Eagle on a Brown Falcon Falco berigora). A breeding by breeding Wedge-tailed Eagles (JO & ST pers. obs.). Wedge-tailed Eagle also robbed a Little Eagle, in the Several other Little Eagle nesting territories included neighbouring Little Eagle territory in peri-urban Canberra in earlier studies (Olsen et al. 2010, 2013a) have since (Lands End), of a freshly caught Rabbit kitten (SJSD pers. been abandoned, although still occupied by Wedge-tailed obs.). During the study period, a pair of Wedge-tailed Eagles (JO & ST pers. obs.). There have also been cases Eagles replaced one Little Eagle pair that had disappeared, of extended and failed egg incubation after female Little and a pair of Wedge-tailed Eagles ranged to the vicinity of Eagles abandoned territories (examples of desertions and another Little Eagle nest after the female Little Eagle had interactions in Figures 3–5). abandoned this nest (JO & ST unpubl. tracking data). Two Discussion

The prey profile of the Little Eagle in the present study is similar to that for the two earlier studies in the ACT (Olsen et al. 2010, 2013a), and to that reported for other parts of where Rabbits are important prey (as reviewed by Marchant & Higgins 1993 and Debus 2017). The high number of insects taken in our study in 2011–2018 (mainly beetles at the nest and roost of a juvenile at one site in summer 2012 and again in 2013) is here considered a sampling artefact, rather than a trend. Rae et al. (2018, 2019, 2020) also found Rabbits to be important in the diet of Little Eagles in the ACT and adjoining NSW in 2017–2019. The dietary proportions that they found in orts only, particularly for 2017, are similar to Figure 3. Egg in Little Eagle nest, Molonglo River, ACT, 20 those that we found for orts only in 2011–2018, although November 2005; the egg was abandoned by the female. Rabbit remains increased in proportion in their 2018 and Photo: Jerry Olsen & Susan Trost 2019 samples.

Figure 4. Little Eagle incubating, Black Mountain, ACT, Figure 5. Little Eagle defending territory against Wedge- 20 November 2019; the nest was subsequently deserted. tailed Eagle, ACT, 13 August 2017; the Little Eagles failed Photo: Jerry Olsen & Susan Trost to breed in that season. Photo: Jerry Olsen & Susan Trost. 24 Australian Field Ornithology S.J.S Debus et al.

from eagle nests both have their inherent biases, and underestimate total intake (Sharp et al. 2002; Parker et al. 2007), so MNI from a combination of sources seems a reasonable balance (Olsen et al. 2010). The observations of Rae et al. (2020) reinforce our observations and conclusions on competitive interactions between Little Eagles and Wedge-tailed Eagles. Rae et al. (2020) showed a photographic record of a pair of Wedge- tailed Eagles interfering at the nest of a pair of Little Eagles, repeatedly visiting the nest and stepping on one of two eggs before the Little Eagles ultimately abandoned the nest. This action was seemingly to displace the Little Eagles from the nest, which from its structure appears to have been built by the Little Eagles. A colleague also obtained a photographic sequence of attempted predation on a Little Eagle by a Wedge-tailed Eagle in Victoria (Figure 6). Olsen et al. (2019) questioned whether drought had any effect on the breeding success of Wedge-tailed Eagles in the ACT. Rabbits were equally important in the diets of Figure 6. Last in a sequence of five frames of a Wedge- Brown Goshawks near Canberra during 2002–2010, and tailed Eagle attacking an adult dark-morph Little Eagle Goshawk numbers had not declined there (Olsen et al. with apparently predatory intent, southern Victoria, 2020. 2018; Olsen 2019). Larkin et al. (2020) did not investigate Photo: Bernie McRitchie the relationship between Little Eagle breeding success and Rabbit abundance, but they found high fledgling productivity in 2018 during an increasingly dry period. It Our findings reinforce the dietary importance to Little remains to be determined whether the severe 2018–2019 Eagles of birds, as also found by Rae et al. (2018, 2019, drought per se has had an effect on the Little Eagle’s 2020). Many such birds inhabit woodland and wooded diet, breeding success and/or territory occupancy in the rural land, as do the few reptiles taken. There was little to ACT, as other explanations are possible for changes in its suggest in the 2011–2018 ACT prey profile that there has demographics in that region. been a major shift in the availability of key prey species, at least as judged from dietary proportions compared with In 2019, a well-funded team of 10 researchers found past studies. The novel prey species taken in the present only three successfully breeding pairs of Little Eagles in study might have been in response to the availability of the ACT (Rae et al. 2020), fewer than the four successfully typical prey, or simply a function of increasing sample size breeding pairs reported by non-funded volunteers in 2008 over time. In 2019, Rae et al. (2020) also recorded Common (Olsen et al. 2009). As predicted by Olsen and Fuentes Ringtail Possum as a food item, confirmed scavenging in (2005) and Debus (2017), interference from Wedge-tailed the form of an adult kangaroo paw being brought to a nest, Eagles and habitat loss from property development were and recorded a further novel prey item (Red Fox cub). implicated in the low number of successfully breeding pairs in 2019 (Olsen et al. 2020). Other causal factors have yet to Wedge-tailed Eagles are thriving on the abundant be verified. We encourage testing alternative hypotheses macropod population in the ACT, and becoming bolder in on the low breeding success of Little Eagles in the ACT: (i) the post-persecution era, showing increasing willingness breeding success will improve when the drought breaks to nest close to human settlements (Fuentes et al. 2007). (Rae et al. 2020), vs (ii) breeding success of ACT Little This heavy kangaroo predation differs from elsewhere in Eagles will remain low after the drought breaks because south-eastern Australia where the two eagle species co- high-quality Little Eagle habitat has been lost to housing exist (see e.g. dietary studies in Debus 2017). The rabbit developments and breeding Wedge-tailed Eagles, leaving calicivirus should have been effective in the ACT, but the degraded (marginal) habitat where Little Eagle breeding virus is least effective in cold, wet climates (e.g. Olsen et attempts cannot be completed (Olsen 2018, 2019; Olsen al. 2014), and the virus failed in the ACT during the period et al. 2017, 2020). In the present context we also note the of the present study on eagles (ACT Government 2020). need for open, transparent research communication (see Rabbits were abundant at one Wedge-tailed Eagle nest- Driscoll et al. 2020). site where they were the main prey. As in all earlier studies, Sheep/lambs were taken in very low proportions by the Wedge-tailed Eagles, compared with the many macropods Acknowledgements and Rabbits taken, and some Sheep were certainly We thank Georgeanna Story for analysing the prey items. scavenged. Particular thanks go to Dalice Trost, Roger Williams, Colin The comparisons of dietary metrics over time may have MacLaren, Darren Rosso, Thomas Mungoven, Christie Gould, Alison Mungoven, Brian Summers, Peter Galvin, Mark Sweaney, been influenced to a small degree by slight differences in Michael Maconachie, James Overall, Jeff van Aalst, Lizabeth the way MNI was calculated in the latest study, compared Collier, Joe Clifton, Geoffrey Dabb, Michael Lenz, Kym Bradley, with the two earlier studies. However, all such studies of Nic Mikhailavich, Tony Ashton, Rosemary Blemings, and to necessity included an element of estimation, especially for Naomi Clarke and Nathan Perring of the Australian Bird and Bat biomass consumed. Data obtained from orts and pellets Banding Scheme. We thank Tom Aumann, James Fitzsimons Breeding diets of Little Eagle and Wedge-tailed Eagle, ACT, 2011–2019 25

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Pacific Conservation Biology 26, 258–268. Olsen, P. (2018). Notes on the breeding ecology of Little Eagles Mallinson, D., Olsen, P D. & Olsen, J. (1990). A note on the in the ACT in 2017/2018. Canberra Bird Notes 43, 186–193. breeding of the Little Eagle Hieraeetus morphnoides and other Rae, S., Mulvaney, M., Fletcher, D., Wimpenny, C., Brawata, raptors on Mt Mugga, ACT. Corella 14, 88–91. R., Kiggins, R., Stol, J., Davies, M., Roberts, D. & Olsen, P. Marchant, S. & Higgins, P.J. (Eds) (1993). Handbook of Australian, (2020). The breeding success and diet of Little Eagles in the New Zealand & Antarctic Birds, Volume 2: Raptors to Lapwings. ACT and nearby NSW in a dry year, 2019. Canberra Bird Notes Oxford University Press, Melbourne. 45, 158–166. Olsen, J. (2014). Australian High Country Raptors. CSIRO Rae, S., Wimpenny, C., Mulvaney, M., Davies, M., Fletcher, D., Publishing, Melbourne. Roberts, D. & Olsen, P. (2019). Preliminary results from study Olsen, J. (2018). Eleven historic breeding territories of ACT Little of Little Eagles in the ACT and nearby NSW in 2018–2019. Eagles is an underestimate – a reply to Olsen and Rae (2017). Canberra Bird Notes 44, 145–151. Canberra Bird Notes 43, 120–131. Sharp, A., Gibson, L., Norton, M., Ryan, B., Marks, A. & Semeraro, Olsen, J. (2019). Telemetry and colour-banding confirm L. (2002). An evaluation of the use of regurgitated pellets and predictions about Little Eagle migration and territory desertion. skeletal material to quantify the diet of Wedge-tailed Eagles, Canberra Bird Notes , 241–249. 44 Aquila audax. Emu 102, 181–185. Olsen, J. & Fuentes, E. (2004). Preliminary Report on the Effect of the Development of the Molonglo Valley on the Community of Birds of Prey. Unpubl report to ACT Planning & Land Authority, Canberra. Received 25 June 2020, accepted 18 October 2020, Olsen, J. & Fuentes, E. (2005). Collapse in numbers of breeding published online 15 February 2021 Little Eagles in the Australian Capital Territory. Canberra Bird Notes 30, 141–145. Olsen, J., Cooke, B., Trost, S. & Judge, D. (2014). Is Wedge-tailed Eagle, Aquila audax, survival and breeding success closely Note added in proof. Jerry Olsen passed away on 30 January linked to the abundance of European Rabbits, Oryctolagus 2021. He was the driving force behind this and other recent cuniculus? Wildlife Research 41, 95–105. collaborative papers on raptors in Australian Field Ornithology. Olsen, J., Debus, S.J.S., Judge, D. & Rose, A.B. (2013a). Diets of An obituary will appear in due course. Wedge-tailed Eagles Aquila audax and Little Eagles Hieraaetus morphnoides breeding near Canberra, 2008–2009. Corella 37, 25–29. 26 Australian Field Ornithology S.J.S Debus et al.

Appendix 1. Breeding diet of the Little Eagle in the ACT, 2011–2018: estimated MNI based on orts and pellets. For explanation of MNI and adjusted biomass, see methods; n = number; * = species not previously recorded in the Little Eagle diet at the time of this study (pre-2018).

Prey species Weight (g) n % n Adj. biomass % biomass

Common Brushtail Possum Trichosurus vulpecula 2880 3 1 1487 3 *Common Ringtail Possum Pseudocheirus peregrinus 900 1 <1 496 <1 Eastern Grey Kangaroo Macropus giganteus 23,000 1 <1 496 <1 Macropus sp. juvenile 3000 1 <1 496 <1 European Rabbit Oryctolagus cuniculus 1500 68 29 33,728 62 Black Rat Rattus rattus 280 1 <1 232 <1 Cat Felis catus (juvenile?) 1000 1 <1 496 <1 Total mammals 76 33 37,431 65

Domestic Chicken Gallus gallus 1000 1 <1 592 1 Australian Wood Duck Chenonetta jubata 810 1 <1 648 1 Rock Dove Columba livia 310 2 1 496 <1 *Common Bronzewing Phaps chalcoptera 330 1 <1 264 <1 Crested Pigeon Ocyphaps lophotes 210 1 <1 185 <1 *Tawny Frogmouth Podargus strigoides 326 1 <1 261 <1 Brown Goshawk Accipiter fasciatus 460 1 <1 368 <1 *Sacred Kingfisher Todiramphus sanctus 40 1 <1 36 <1 Laughing Kookaburra Dacelo novaeguineae 340 1 <1 272 <1 Galah Eolophus roseicapilla 335 6 3 1608 3 Crimson Rosella Platycercus elegans 135 14 6 1663 3 Eastern Rosella Platyercus eximius 106 8 3 746 1 Rosella Platyercus sp. 110 5 2 484 <1 *Brown Treecreeper Cimacteris picumnus 34 2 1 62 <1 Superb Fairy-wren Malurus cyaneus 10 1 <1 9 <1 Pied Currawong Strepera graculina 270 2 1 475 <1 Australian Magpie Gymnorhina tibicen 330 10 4 2640 5 Magpie-lark Grallina cyanoleuca 90 3 1 238 <1 Common Starling Sturnus vulgaris 75 7 4 462 <1 Common Myna Acridotheres tristis 116 3 1 102 <1 Unidentified bird 150 30 13 3960 6 Unidentified juvenile bird 20 1 <1 18 <1 Total birds 102 44 15,589 27

Eastern Bearded Dragon Pogona barbata 400 1 <1 Dragon (Agamidae) 400 2 1 640 <1 Eastern Blue-tongue Tiliqua scincoides 400 10 4 3200 6 Shingleback Tiliqua rugosa 590 1 <1 472 <1 Total reptiles 14 6 4312 8

Beetle (Coleoptera) 2 34 15 68 <1 Grasshopper (Orthoptera) 2 6 2 12 <1 Total insects 40 17 80 <1

Total 232 100 57,412 100 Breeding diets of Little Eagle and Wedge-tailed Eagle, ACT, 2011–2019 27

Appendix 2. Breeding diet of the Wedge-tailed Eagle in the ACT, 2011–2019: estimated MNI based on orts and pellets. For explanation of MNI and adjusted biomass, see methods; n = number.

Prey species Weight (g) n % n Adj. biomass % biomass Common Wombat Vombatus ursinus 26,000 3 1 7638 3 Common Brushtail Possum Trichosurus vulpecula 2880 6 2 11,578 4 Common Ringtail Possum Pseudocheirus peregrinus 900 4 1 2400 <1 Eastern Grey Kangaroo Macropus giganteus 23,000 22 9 56012 19 Eastern Grey Kangaroo juvenile 3000 13 5 26,000 9 Common Wallaroo Macropus robustus 21,000 1 <1 2546 <1 Macropus sp. 21,000 1 <1 2546 <1 Macropus sp. juvenile 3000 11 4 22,000 7 Swamp Wallaby Wallabia bicolor 15,000 1 <1 2546 <1 European Rabbit Oryctolagus cuniculus 1500 61 24 61,305 20 Brown Hare Lepus capensis 4000 1 <1 2546 <1 Sheep/lamb Ovis aries 40,000 12 5 30,552 10 Cat Felis catus 4200 10 4 25,460 8 Red Fox Vulpes vulpes 9000 6 2 15,276 5 Total mammals 152 59 268,405 89

Grey Teal Anas gracilis 504 1 <1 403 <1 Pacific Black Duck Anas superciliosa 1040 1 <1 832 <1 Australian Wood Duck Chenonetta jubata 810 4 1 2592 <1 Duck (Anatidae) 700 1 <1 560 <1 Rock Dove Columba livia 310 1 <1 248 <1 Little Eagle Hieraaetus morphnoides 870 2 <1 1392 <1 Laughing Kookaburra Dacelo novaeguineae 340 3 1 816 <1 Brown Falcon Falco berigora 590 1 <1 472 <1 Gang-gang Cockatoo Callocephalon fimbriatum 251 1 <1 221 <1 Galah Eolophus roseicapilla 335 11 4 2948 <1 Sulphur-crested Cockatoo Cacatua galerita 804 10 4 6432 2 Corella Cacatua sp. 500 2 <1 800 <1 Crimson Rosella Platycercus elegans 135 7 3 832 <1 Eastern Rosella Platyercus eximius 106 3 1 280 <1 Rosella Platyercus sp. 110 3 1 290 <1 Pied Currawong Strepera graculina 270 2 <1 475 <1 Australian Magpie Gymnorhina tibicen 330 8 3 2323 <1 Magpie/currawong 300 1 <1 240 <1 Australian Raven Corvus coronoides 645 8 3 4128 1 Raven Corvus sp. 590 1 <1 472 <1 Magpie-lark Grallina cyanoeluca 90 1 <1 79 <1 White-winged Chough Corcorax melanorhamphos 330 1 <1 284 <1 Common Starling Sturnus vulgaris 75 2 <1 132 <1 Passerine (Passeriformes) 30 1 <1 27 <1 Unidentified large bird 1000 3 1 2010 <1 Unidentified bird 150 16 6 2112 <1 Total birds 95 38 31,400 10 28 Australian Field Ornithology S.J.S Debus et al.

Appendix 2 continued

Prey species Weight (g) n % n Adj. biomass % biomass

Eastern Bearded Dragon Pogona barbata 400 1 <1 320 <1 Eastern Blue-tongue Lizard Tiliqua scincoides 400 3 1 960 <1 Total reptiles 4 1 1280 <1

Fish 1000 2 <1 1600 <1

Beetle (Coleoptera) 2 2 <1 4 <1 Grasshopper (Orthoptera) 2 1 <1 2 <1 Total insects 3 1 6 <1

Total 256 100 302,691 100