Ecology of Rhinonicteris aurantiain the Pilbara

by Norm McKenzie & Bob Bullen

Pilbara form:

EPBC Act (2012): Vulnerable Criteria 1, 2 and 3

meets IUCN criteria for Vulnerable A3c, D2

Both forms:

Rare or likely to become extinct (WA Wildl Cons Act, 1950)

Vulnerable (WA DEC Priority Fauna list)

Rhinonicteris aurantia

Image: Mark Cowan

A small tropical insectivorous bat (7–11g, 30 cm wingspan)

A monotypic genus endemic to Australia, but Oligo-Miocene (20my BP) & Pliocene (4my BP) deposits from NW Queensland include several species

The Pilbara form (PLN) is the species’ only arid zone population, has been geographically isolated for 30,000 years or more

and shows small skull, noseleaf, echolocation and DNA differences

• Roosts in caves (and old mines)

• Colonies range from 10 to, exceptionally, 20,000 individuals

• Mate in the mid-dry season & a single young is born in Dec, so lactation occurs during the productive (wet) season. Growth is so rapid that weaned by late-Feb

• Females are reproductively mature at 7 months, males at 18 months

• Unable to enter torpor, and must feed almost every night

• Emerge at dusk to hunt, catching their insect prey on the wing while in rapid, zig-zag flight within a few metres of the vegetation & ground

Foraging EcologyUnlike other leaf-nosed bats, it uses rapid flight and abrupt

turns to catch its prey (‘stall turns’ or ‘80o of bank’ at 18-22 kph).

This evolutionary choice demands a variety of specialised airframe design features (TEAR=17), including large flight muscles (16% of mbat) that can generate great lateral forces

These features are energetically expensive, so its persistence in the arid Pilbara depends on:

1. The physiologically benign day-roosts found deep underground in humid, temperature-stable caves − it’s relatively small heart muscle leaves no options. Old partially-flooded mines are ideal, but it can use less humid roosts in summer.

2. Very high rate of food intake while hunting − to fuel the big flight muscles, especially during lactation.

Foraging Ecology (cont)

They commute from roost, or between foraging areas, at ca. 28 kph and probably forage no more than an half an hour’s flight from a roost.

If insect biomass is high enough at the time, PLN will forage in any habitat (scree slope, sandplain etc), but reliably productive riparian zones are favoured.

Roost Types

1. Maternity roost: large permanent colony with pregnant and/or lactating females and young present seasonally.

2. Diurnal roost: occupied by one to many individuals during the day, but may move on the next night.

3. Nocturnal roosts: regular transient use, but no evidence of daytime occupation.

All three roost-types underpin the PLN’s regional population, the last two types by allowing it expand its foraging range.

Known PLN localities in early-2010The Pilbara Biological Survey showed that PLN are more common and widespread than previously recognised in both the Hamersley and Chichester sub-regions.

Threats

The Pilbara is arid, so this high energy bat is vulnerable if:1. its roosts are destroyed,2. its accessible foraging habitat is reduced or degraded,

especially when females are lactating.3. humans disturb its roosts.

Since 2010, mining industry consultants like Bob Bullen have carried out detailed PLN surveys over virtually the entire region.

Many additional roosts in natural caves have been identified in both the Hamersley and Chichester sub-regions

… more on this in the other presentations

Threats (cont)

PLN natural maternity roosts are virtually confined to deep humid caves in hard, iron-rich rock strata. These are vulnerable to iron mining operations unless a buffer zone is respected. – For instance, drilling must not penetrate the cave cavity --

heat/humidity loss; oil mist

Maternity roosts are also found in old underground gold and copper mines but these are collapsing, flooding or being open cut.

Even though these mines didn’t exist prior to 1880, there is an urgent need to stabilise some because of their location and colony size

Threats (cont)

There is no evidence that the PLN’s population has declined or that its area of occupancy has contracted, but de-listing the PLN is not recommended because the natural roosts known in the Pilbara are confined to banded ironstone strata that may be mined.

Unconstrained mining will reduce the population by >30% over the next 15 years (= 3 generations).

Without intervention and regionally focused management, most such roost sites will be destroyed over the next 30-50 years.

Research Priorities• Locate all maternity and diurnal roosts, then

– assess the strata containing each roost for commercial potential

– map the extent of the cave structure (buffer zone must encompass the entire cave system)

– census the roost, thence estimate population size– document microclimates required in PLN maternity and

diurnal roosts across the seasons – Determine and monitor population’s age structure and

recruitment success– identify roosts in iron deposits proposed to be mined, and

assess extent of proposed roost destruction Pilbara-wide– assess buffer zone distances and effectiveness w. r. to

various mining operations (blast intensity, drilling etc)

Research Priorities (cont)

• PLN night roosts -- how and when used:– Are they used to expand foraging range seasonally? – Do PLN feed on the mosquitoes etc that refuge in these

caves/caverns

• Assess artificial roost options:– Can we excavate deep adits into low-grade hard rock

strata ($8000 /m), rather than burying structures in spoil dumps, and provide artificial maternity roosts with a viable service life?

– Monitor PLN colonisation rates and longer-term usage.

Research Priorities (cont)Map foraging habitats around each roost, and

assess– temporal dynamics in PLN habitat-use: its

dependence (if any) on continuously productive habitat mosaics, such as nearby riparian zones, as well as on mosaics that are seasonally or ephemerally productive (e.g. after rain).

– proximity to maternity roosts of foraging habitats used by lactating females, other adults, and sub-adults seasonally, and

– how different roost-types are networked to access additional foraging habitat remote from the maternity roosts seasonally.

Research Priorities (cont)

• Calculate PLN foraging energetics– Food capture rates to meet daily metabolic needs, for both

breeding and non-breeding adults (e.g. a lactating CI pipistrelle had to eat one 7mm insect / minute for 4 hours every night)

• Resolve taxonomy of PLN populations: – document genetic structure of PLN populations in detail,

both within the Pilbara and in relation to the Kimberley form.– evaluate extent of movement between/within different PLN

populations– compare physiological differences between Pilbara and

Kimberley forms in terms of arid zone adaptations

Conservation Actions

Develop a set of standard guidelines for mining proponents to follow if this species occurs in their project area:– For management and protection of roost sites and

foraging habitat– monitoring protocols with defined trigger points and

contingency actions for diurnal and maternity roost sites

Create a protected area system of natural caves and old mines with significant colonies:– vested reserves where possible; if not, – seek conservation covenants on private and

leasehold lands, particularly for maternity roosts

Conservation Position

Unlike the Christmas Island Pipistrelle that became extinct in 2010, the Orange Leaf-nosed Bat:

-- Is a monotypic genus endemic to Australia.

-- Is the sole survivor of an Oligo-Miocene radiation.

-- Has a high energy foraging strategy unique among megabats

The PLN is the only arid-zone genotype of the species.

Its collapse would attract international attention.

Echolocation

In the Pilbara there are two bat lineages that use ultrasonic calls to avoid obstacles and locate prey:

1. Sixteen microbat species, that use frequency modulated calls (10–75 kHz),

2. One megabat, the PLN, that uses ‘constant frequency’ calls at much higher frequencies (116–122 kHz).

High frequency calls are severely attenuated by the air so, even when R. aurantia is flying directly towards a bat-detector microphone, its calls are seldom detected at > 3m range

PBS bat detection site PLN forage at 5–6 ms-1 & can’t be detected at >3 m range. It was detected in 11 of 69 sites sampled during the survey (av. 2 nights/site = 5 hrs) suggesting that it is widespread.