National recovery plan for the Black-eared Miner Manorina melanotis 2002 - 2006

Conservation of old-growth dependent mallee fauna
Prepared by David Baker-Gabb for the Black-eared Miner Recovery Team, February 2001
(Revised February 2003)

2. The Black-Eared Miner

Description

The Black-eared Miner is one of four species of colonial and co-operatively breeding honeyeaters in the genus Manorina. The Black-eared Miner has a stocky build, is about 20 cm long and is dark grey above, paler below, with a dark facial mask and orange-yellow bill and legs. The species is most similar in appearance to the Yellow-throated Miner Manorina flavigula, but can be distinguished readily in the field by its much darker rump, lack of pale terminal band on the tail and a greater contrast between the colour of the feathering on the lower jaw and throat (Clarke and Clarke 1999a).

Taxonomy

There has been controversy over the taxonomic status of the Black-eared Miner. Various authors have considered it a species (Wilson 1911; Schodde 1975; Christidis and Boles 1994; Clarke et al in press), a subspecies or morphological variant of the Yellow-throated Miner (Matthews 1912, 1913; RAOU 1913; Silveira 1995; Schodde and Mason 1999) and a subspecies of the Western Australian 'Dusky Miner' Manorina flavigula obscura (Ashby 1922; Matthews 1925; RAOU 1926).

There are morphological and behavioural differences between Black-eared and Yellow-throated Miners (Ford 1981; Joseph 1986; Starks 1987; McLaughlin 1990, 1992; Clarke et al in press), and evidence for marked ecological separation exists (Joseph 1986; McLaughlin 1992). This morphological and ecological evidence supports the contention that the two miners are separate species (Fitzherbert et al 1992). Molecular assessment by Christidis (1995) also indicated that the Black-eared Miner is a distinct species. Moreover, Clarke et al (in press) showed that Black-eared and Yellow-throated Miners were clearly separable on phenotypic characters prior to extensive modification of mallee habitat that occurred after 1950. They argue that the Black-eared Miner should be afforded full species status given that widespread hybridisation is a recent development facilitated by human disturbance of their habitat.

Black-eared Miners can interbreed with Yellow-throated Miners, resulting in fertile hybrids that display a range of intermediate plumages (Ford 1981; McLaughlin 1990, 1993a). Clarke and Clarke (1999a) have developed a simple guide to distinguish Black-eared Miners from hybrids and Yellow-throated Miners in the field.

Distribution

The historical distribution of the Black-eared Miner included the Murray Mallee of Victoria, South Australia and New South Wales (Blakers et al 1984; Joseph 1986; Starks 1987) (Figure 1). The Black-eared Miner's current distribution (Figure 2) is much reduced with over 95% of known colonies in the Bookmark Biosphere Reserve (Clarke and Clarke 1998).

The only recent records from New South Wales are of about five hybrid colonies (Franklin 1996; Boulton and Clarke 2000a). In Victoria there are six known widely-dispersed colonies of hybrid birds (Clarke and Clarke 1999b). In South Australia there are over 200 known colonies in the Bookmark Biosphere Reserve and one at Glenburr Scrub near Murray Bridge (McLaughlin 1996; Clarke and Clarke 1999b). Small captive colonies of hybrid birds have been established at three zoos.

Habitat Critical for Survival

The Black-eared Miner inhabits Shallow-sand Mallee and Chenopod Mallee in both the Sunset Country of Victoria and the Bookmark Biosphere Reserve in South Australia (McLaughlin 1992; Muir et al 1999). In both States the vegetation is dominated by multi-stemmed mallee eucalypts, including Eucalyptus dumosa, E gracilis, E oleosa and E socialis, usually in association with a ground layer dominated by either Porcupine Grass Triodia scariosa, or shrubs of the families Chenopodiacae and Zygophyllaceae (Starks 1987; McLaughlin 1992; Muir et al 1999).

Black-eared Miners occur predominantly in old-growth habitats that have not been burnt for at least 40 years, although post-fire regenerating mallee of 5-10 years or older may provide occasional foraging habitat (Starks 1987; C Silveira and J McLaughlin unpubl). In the Bookmark Biosphere Reserve and Tarawi Nature Reserve in NSW >80% of the mallee is older than 40 years and hence suitable for breeding birds. In Victoria where there is much less old-growth mallee, the age and distribution of cohorts of mallee regenerating from fires have been mapped and digitised so that the amount of critical habitat and potential critical habitat can be calculated.

Within large areas of contiguous mallee in Bookmark Biosphere Reserve, sites with highest quality colonies of Black-eared Miners are more than 5 km from dams and man-made clearings (Clarke and Clarke 1999b, Muir et al 1999). In contrast, all known Yellow-throated Miner colonies in the Bookmark region have been located within 2 km of permanent water and man-made clearings. The extensive areas of mallee that have remained unburnt for over 40 years that Black-eared Miners need are also important for other nationally threatened birds such as the Malleefowl and hollow-nesting Major Mitchell's Cockatoo (Benshemesh 1999, Garnett and Crowley 2000).

In Victoria, colonies known to have contained Black-eared Miners were in blocks of contiguous mallee vegetation larger than 12,000 ha (McLaughlin 1994). In South Australia and New South Wales all but one known colony occurs in areas of contiguous mallee larger than 100,000 ha. Black-eared Miners were once known to occur in small remnant patches of mallee (McGilp and Parsons 1937; Rix 1937; McGilp 1943) which were probably occupied immediately following large-scale clearing, but prior to the expansion into and subsequent habitation of these areas by Yellow-throated Miners (Starks 1987). Even larger isolated blocks of suitable mallee such as the reserves at Bronzewing (20,000 ha) and Annuello (35,000 ha) have proved unable to retain viable populations of Black-eared Miners and protect them from genetic swamping in the medium term (Boulton and Clarke 2000b).

Life History and Social Organisation

Colony size and quality

Like other members of the genus Manorina, the Black-eared Miner is colonial. Each colony typically contains several breeding pairs whose nests may be as little as 15 m apart. When breeding, the species is co-operative with up to 12 juvenile and adult non-breeding individuals (helpers) assisting at a nest. Helpers are predominately male (E Moysey unpubl data), as is the case with other miners (Dow 1978; Clarke 1988). Larger colonies (10+ individuals) contain several well-defined social units. However, the colony still functions as a whole to repel potential predators and other undesirable intruders. Breeding colonies in the Bookmark region contain an average of 18.4 individuals (range 8-40+; Clarke and Clarke 1999b). In Victoria where the species is declining, McLaughlin (1994) calculated the then average number of birds in a colony was 6.3.

All colonies in Victoria that have contained Black-eared Miners in recent times have also contained hybrid birds (Starks 1987; McLaughlin 1990, 1994). Colony quality has continued to decline in Victoria (Boulton and Clarke 2000b). In South Australia colony quality is much higher with 38% of 87 ranked colonies consisting of exclusively or mainly pure Black-eared Miners, and colony quality is also stable there (Boulton and Clarke 2000b).

Effective population size

In the Bookmark Biosphere Reserve there are over 200 colonies (Clarke and Clarke 1999b) containing more than 3,600 birds, of which about 1,400 are Black-eared Miners and the rest are hybrids. The adult sex ratio in colonies is biased towards males, some of which help at nests but do not breed. Based on adult sex ratio data (64% male, Ewen et al in press), and an average of five breeding pairs per colony (R Boulton unpubl data), the effective breeding population in Bookmark is about 2,000 mature individuals, including 760 Black-eared Miners. There are about 50 hybrids in New South Wales (Boulton and Clarke 2000a). After the translocations in 2000, there are about 150 Black-eared Miners and hybrids in Victoria (Clarke and Clarke 1999b, BeM Recovery Team unpubl).

Territoriality and seasonal movement

When breeding, adults typically forage short distances from the nest (up to 0.8 km; E Moysey unpubl data). When not breeding birds move as groups (either as an entire colony or in smaller aggregations) over greater distances to forage. Non-breeding birds remain within a non-breeding territory of several hundred hectares and sightings of marked individuals have been made up to 2 km from the core home range during these non-breeding periods (Clarke and Clarke 1999b). A colony of 11 birds in Victoria occupied a 16 ha core home range and a total home range in excess of 40 ha (Backhouse et al 1997). A colony containing 40+ individuals in Bookmark occupied a core breeding range of 12 ha and a total non-breeding home range of 100+ ha (E Moysey unpubl data). At their greatest density colonies breed approximately 2 km apart in the Bookmark region (approximately one colony per 400 ha of total available habitat) (Clarke and Clarke 1999b). However, in Victoria where the species is almost extinct, colonies occurred at densities of about one colony per 1450 ha of apparently suitable habitat in 1993 (McLaughlin 1994).

Social organisation

The Black-eared Miner is monogamous and pairs appear to remain together for life, only re-pairing upon the loss of a mate (Clarke and Clarke 1999b). Breeding males within a colony are close relatives, whereas females, the dispersing sex, are not (E Moysey unpubl data). Adult population sex ratio of breeding colonies in the Bookmark region is significantly male biased (64% male; J Ewen unpubl data). In contrast the sex ratio of nestling Black-eared Miners is significantly female biased (61% female). Since the nestling sex ratio is significantly different from the sex ratio of the adult population it would appear that females are experiencing higher mortality than males between fledging and gaining reproductive status (Ewen et al in press).

Breeding and recruitment

Black-eared Miners are opportunistic breeders, breeding when conditions are suitable. Nests have been found in all months. However, breeding typically extends from September to December. Widespread breeding has also been observed from March to May on three occasions (Backhouse et al 1997, Boulton and Clarke 2000b). Breeding appears to be linked to rainfall events during mild to warm seasons which promote elevated insect activity, increased lerp abundance and flowering events, both of mallee and understory shrubs. Within a breeding period, birds will usually re-build and lay within two weeks of nest failure. Nests are usually built in mallee eucalypts, either in upright forks, amongst small twigs and foliage, or on epicormic shoots, between 1.5-4.5m above ground (McLaughlin 1990; BANRS). The modal clutch size is three (BANRS).

For a large colony in the Bookmark Biosphere Reserve reproductive success was high for a honeyeater, with 56 % of nests containing eggs producing at least one fledgling (E Moysey unpubl data). In 2000, 38 (26%) of 145 recorded breeding attempts produced fledglings resulting in high rates of recruitment. However, reproductive success of nests from several Victorian sites has been reported to be substantially lower (J. McLaughlin unpubl data in Backhouse et al 1997).

Foraging behaviour and diet

The Black-eared Miner eats mainly invertebrates and lerp (the sugary exudate produced by psyllids). Prey is obtained mainly from gleaning and probing decorticating bark, limbs and twigs of eucalypts and gleaning from foliage, although birds will also forage on the ground and hawk for flying insects (McLaughlin 1990). Nectar from Eucalyptus spp, Eromophila spp and Grevillea huegelii is also taken. In captivity Black-eared Miners are successfully maintained on a diet of commercial honeyeater and lorikeet mix and invertebrates (Clarke and Clarke 1999b).