Mangrove Ants adapt to nesting underwater

mangrove ants
One nest entrance is circled, and another was just behind me as I took this shot

When I was wandering along the bank of Ross River near the Bowen Road bridge a few months ago, I looked down, saw a perfectly ordinary looking ants’ nest and a moment later thought, “Hey! That’s odd! That would be under water at high tide!”

The ants were perfectly at home, however, running in and out of their nest entrance. Odd indeed. Continue reading “Mangrove Ants adapt to nesting underwater”

Extreme mangroves

mangrove creek
Mangroves line Screw Creek where it enters Anderson’s Inlet

I grew up with mangroves as a normal feature of my coastal landscape but never really understood how abnormal that was for a Victorian, which is what I was at the time, until very recently.

It was pure luck, really. I grew up in and near a South Gippsland town half-way between Melbourne and Wilson’s Promontory and our nearest beach was Inverloch, on Anderson’s Inlet; and we stopped at Tooradin, on the northern edge of Westernport Bay, every time we went to Melbourne. I never knew that mangroves were only found along 2% of the Victorian coastline or that the mangroves in Corner Inlet near Wilson’s Prom were the world’s highest-latitude mangroves, at 38 deg. 45′ South. MangroveWatch Australia has all the details if you want more, but there isn’t a lot more to tell: there is only one Victorian species, Avicennia marina, known locally as the White Mangrove (and elsewhere as the Grey Mangrove; be wary of common names!), and even that one struggles to survive except in sheltered spots or to get to any height greater than a metre.

mangroves
Looking across Sawtell’s Inlet, Tooradin, to the mangroves
leaves and yellow berries
Foliage and fruit of the White Mangrove at Tooradin

Fast forward to 1990 and my arrival in Townsville … mangroves all over the place, and again I took them from granted – because I had grown up with them, of course! But where Victoria had one species and a total area of a mere 60 km2, Queensland has 39 and 4000 km2. They are not all stunted little things, either – some reach 25 metres; once again, MangroveWatch has all the information but this time there is far more of it.

I have often written about them on Green Path, though usually as a background to the wildlife (big or little) they support – butterflies at Cape Hillsborough or Ross Creek, Rainbow Bee-eaters in the city, and so on. This link will take you to all references to them.

Blue Tigers in the Mangroves

looking across mangroves to a bay
Mangroves at Cape Hillsborough National Park – looking south, with the boardwalk out of sight to the left

Back to Cape Hillsborough … the National Park is a peninsula and there’s a big area of mangroves on the broad, low-lying neck between the resort and the mainland. The “Diversity Boardwalk” loops through them and returns via higher ground to illustrate how land-forms shape plant communities.

boardwalk through mangrove forest
The beginning of the Diversity Boardwalk

All mangroves are salt-tolerant and don’t mind sand or wet feet but even within the family there is a variety of preferred habitats, and a small difference in height above sea level (even a metre or two) allows bigger mangrove species to thrive, so the boardwalk does earn its name. (Mangrove eco-systems are a huge topic in themselves – you could start with wikipedia if you want to explore them.)

But what about the Blue Tigers? Surely they should be even more famous than the Swamp Tigers of the Sundarbans? Sorry – they are butterflies.

Blue Tigers, Tirumala hamata, are Milkweed butterflies (Danaidae) like the Crows and they have the same habit of getting through the dry (winter) season by congregating in large groups in moist, shady places and doing as little as possible. I have seen groups of Crows on Townsville’s Town Common but was not at all prepared for the enormous flock of Tigers (flock?? cloud? school? flight? flutter? swarm? rabble? kaleidoscope??) I saw near the boardwalk car park.

blue butterflies on red flowers
Blue Tigers feeding on bottlebrush

I amused myself by seeing how many of them I could get into one photo, both in the shade and feeding in full sun on the flowering bottlebrush trees.

blue butterflies on trees
Blue Tigers resting in the shade

The beginning of October, when I saw them, was probably near the end of their resting season. There’s no sense in wasting energy making babies if they are going to starve as soon as they hatch, but as soon as the caterpillars’ food plants start growing again, normal life (i.e. breeding) resumes.

The Tigers weren’t the only butterflies enjoying the bottlebrush near the boardwalk that day; I also saw Wanderers, aka Monarchs (Danaus plexippus) and a Ulysses (Papilio ulysses) there. In the shade of the mangrove trail proper I saw Australian Rustics, Bush-browns and some unidentified Skippers. And I saw another, smaller, aggregation of Tigers on the Beachcomber Cove track, a little way up the hill from its resort end.

A friend in Townsville had this to say about Blue Tigers closer to home:

Blue Tigers … used to overwinter in quite large numbers along the track from Horseshoe Bay to Balding Bay [on Magnetic Island], quite possibly still do though they weren’t there when I walked the track on Saturday [early October], I think too late in the season for them.
Interesting that you saw them in Cape Hillsborough though – a bit cooler there perhaps?
… They are a favourite of mine. I’ve seen them overwintering in lowland vine forest in the Mission Beach/Kennedy Bay and Airlie Beach areas too, as well as the banks of Alligator Creek downstream from the swimming and picnic area – often they are with Crows, but the ones I remember seeing on Magnetic were exclusively, or almost exclusively, tigers.

Ross Creek mangroves and birds

mangroves with stilt roots in water
Mangroves – not a million miles from the city

One of the nice things about Townsville is the network of parks threading through the suburbs. Some of them seem to have no particular reason for existence until the wet season arrives and they become floodways for a day or two, but the most important network is associated with Ross River; the parkland along its banks is almost continuous from the Dam down to the city, and bike paths run through most of its length.

The city centre, however, is not on the river but on a tidal mangrove creek, Ross Creek, which runs from Hermit Park past the Civic Theatre to the ferry terminal; this map may make the situation clearer. Its inland end looks like it connected to the river not too long ago but the river banks have been built up and the creek now just peters out in parkland.

Between them, the River and Ross Creek are wonderful wildlife corridors between the coast and the inland. Vegetation corridors, too, bringing the rich mangrove eco-systems right into the suburbs. The photo above was taken on the upper end of Ross Creek, where Queens Road crosses it. I stop there often on my way home from the city if I have spare time, because fifty metres from the road might as well be a couple of hundred. My last two visits rewarded me with photos of Brown Honeyeaters, a Great Egret, a flock of Little Black Cormorants and a ding-dong battle between a two crows and a brahminy kite.

small olive-brown bird in branches
Brown Honeyeater in the mangroves
Great Egret taking to the air
Great Egret taking to the air
birds against the sky
Little Black Cormorants

The cormorants were just passing through (this time, anyway – a year ago I saw a similar flock on the ground here) but I was able to watch the other two for much longer. I sat for twenty minutes on a low branch of the mangrove tree which the Brown Honeyeater was treating as his home base, repeatedly flying off and returning to sing; and on my next visit I followed the Egret quite a long way upstream as he fished in the shallows, flew a few metres and resumed fishing.