Living on Fish

A while ago I offered a post on some of the huge number of bird species that live by eating insects; the numbers involved are staggering. At least equally so, and in terms of sheer mass probably more so, are the numbers of animals that live wholly or significantly on fish. Mostly I'll be talking about birds again, but not entirely. 

Pied Kingfisher Ceryle rudis, Queen Elizabeth NP, Uganda.

The fish resource, though severely depleted by human overfishing, is extraordinary. One authoritative source puts the annual human wild fish catch at 90-95 million tonnes. It's hard to imagine that in terms of numbers of fish, and of course many animals take fish smaller than those generally consumed by people.

Moreover fish is a food high in energy and protein, so energy-consuming hunting strategies can be profitably applied. The Pied Kingfisher above could well have caught his lunch (and it is a he, with that broad breast band) by hovering, which burns lots of energy. 

Pied Kingfisher hovering, Amboseli NP, Kenya.

Many birds plunge into the water from above, or swim on the surface then dive, and pursue the fish underwater, a high energy game indeed. Many of these birds hunt in flocks, which are sometimes vast, converging on schools of fish which can number millions of potential prey items. To encounter such a hunt is among the most dramatic spectacles nature can afford us.

Cormorants (several species) converging on a huge fish school, Humboldt Current, northern Chile.
This is only a small part of the vast loose flock that streamed out to sea in response to other
birds already there.

Kelp Gulls Larus dominicanus and Black-browed Albatross Thalassarche melanophris in the
Strait of Magellan; upwelling cold waters provide the richest fisheries.

Blue-footed Boobies Sula nebouxii (again a tiny part of a flock of hundreds) smashing into the water
from tens of metres up, Galápagos. Note how they close their wings just before they hit the
water. They have no nostrils, which would be a serious disadvantage here.

Peruvian Pelicans Pelecanus thagus diving, Isla de Chiloé, southern Chile.

To an Australian, seeing the two big brown American pelicans diving from on high is a real surprise. Australian pelicans (which are bigger), hunt by swimming, then dipping their huge bills with elastic pouch into the water. They too often hunt in flocks however, chasing the fish schools, often accompanied by cormorants.

Australian Pelicans Pelecanus conspicillatus and Pied Cormorants Phalacrocorax varius,
Longreach Waterhole near Elliott, Northern Territory.

Australian Pelicans fishing, Canberra. The water here is shallow so they had to turn their
heads side on to submerge them. They scoop up water in the bill pouch and squeeze it out, retaining
fish and other prey items.     

 

Pelicans waiting for fish - sometimes stunned by the turbulence - to come through the lock
at Blanchetown on the River Murray, South Australia. The resting cormorants are
presumably sated; you can catch enough fish to fill your energy needs in
a relatively short time.

The cormorants benefit from the fish stirred up by the bigger birds, and will even snatch fish from the corners of a pelican's beak. They of course do pursue the fish underwater.

Little Black Cormorants Phalacrocorax sulcirostris, fishing in Kinchega NP,
western New South Wales.

Fish are slippery - they have an antibiotic surface slime and very smooth scales for sliding efficiently through the water - so a specialised bill is required. Cormorant bills are strongly hooked.

Little Black Cormorant, Coffs Harbour, NSW.
You'll see the hook better if you click on the picture to enlarge it.

Penguins and petrels and shearwaters have similar hooks.

Flesh-footed Shearwaters Ardenna carneipes, Lord Howe Island.

However many effective fish-eaters do not. Darters - a group of four diving fishers superficially resembling cormorants - tend to stalk along the bottom and ambush their prey rather than actively pursuing it like a cormorant. They have sharp-tipped bills and tend to stab upwards, surfacing and swallowing the stricken fish head-first.

Female Australian Darter Anhinga novaehollandiae with fish.
The weird kink in the neck is due to a hinge between the eighth and ninth
cervical vertebrae which enables the bird to thrust its neck forward like a spear.
The bill actually has little serrations on the inner edges to assist in swallowing.

This can be seen better in other species, including these Royal Spoonbills Platalea regia.

Royal Spoonbills at Jerrabomberra Wetlands, Canberra. The one on the left is swallowing a small fish.
Below you can see the bill serrations if you click on the photo.

These spoonbills are hunting primarily by touch by means of a 'bill tip organ' comprising many thousands of tightly packed sensors both in the tip of the bill and in the upper and lower jaws. These combine touch and taste and cause the bill to snap shut if it encounters something edible. Many birds which hunt food in mud and muddy water have such sensors.

Wood Storks Mycteria americana, Pantanal, south-eastern Brazil.

The really big storks have such organs too, but often their fish prey is so big that they can rely on their vision.

Jabiru Jabiru mycteria with big fish, Pantanal.
Despite the bird's huge size, it struggled for a long time to subdue and swallow this mighty meal.
However I doubt that it needed another one that day!

Saddle-billed Stork Ephippiorhynchus senegalensis, with big catfish (I think),
Amboseli NP, Kenya.

A slightly different use of the bill-tip organ is applied by the fascinating skimmers, three distinctive species in the gull and tern family. Their bottom mandible is much longer than the upper. They fly along the water surface trailing the tip of the bottom one in the water and when it encounters a fish or other food item the bill snaps shut on it.

Black Skimmers Rynchops niger;
Pantanal above, and Isla de Chiloé, southern Chile, below.

Fish-eating birds of prey - fishing eagles, ospreys and even fishing owls - certainly have an appropriate hooked bill, but in fact they inherited that, ready evolved, from non-fishing ancestors. They catch their fish using powerful clawed feet.

Eastern Osprey Pandion cristatus, Hervey Bay, Queensland.
The two closely-related osprey species are found all over the world; they are the only
day-time birds of prey to be exclusively fish eaters. Their large back-hooked claws
differ from those of most fishing eagles, and are adapted to slippery fish.

White-bellied Sea Eagle Haliaeetus leucogaster carrying fish dinner,
Port Macquarie, NSW.

African Fish Eagle Haliaeetus vocifer, Queen Elizabeth NP, Uganda.
The ten species of fishing eagle, found across the globe, are now
regarded as all being in the one genus. Though the claws aren't hooked,
the power of the feet is evident in this photo.

Grey-headed Fish Eagle Haliaeetus ichthyaetu, Sabah, Malaysian Borneo.
Until recently this and another species were regarded as separate from the other
fish eagles; they are even more fish-reliant than the others and it is no coincidence
that they have oprey-like recurved claws.

Fishing owls are found both in Africa and Asia, with three species each; the two groups are quite separate and the African ones differ in being almost exclusively fish-reliant.

Buffy Fish Owl Ketupa ketupu, Kinabatangan River, Sabah.
The African fishing owls plunge their legs into the water like fishing eagles,
but the Asian ones are more fastidious, not liking to get their feathers wet.

The many species of abundant gulls, all over the world, do catch fish, but they also scavenge many fish carcases; these days of course many of these are due to discards from human fishing.

Pacific Gull Larus pacificus, Esperance, Western Australia.

Silver Gull Chroicocephalus novaehollandiae, Cairns, north Queensland.

Many marine mammals (especially seals, sea lions and toothed whales) and some freshwater ones are fish eaters. Of these some of the best-known and most specialised are the otters, a group of highly specialised aquatic weasels, some of them quite large. 

The magnificent Giant Otter Pteronura brasiliensis, here in the Pantanal of Brazil,
showing its beautifully adapted paddle-shaped tail.

Giant Otters sharing - and squabbling over - fish in the Manu section
of Peruvian Amazonia. These two areas are relative strongholds of this superb animal,
which can grow up to 2.5 metres long and weigh over 30kg. Populations though are
tragically depleted by illegal hunting for its fur. They are strongly gregarious.

Neotropical Otter Lontra longicaudis, Pantanal, in a roadside lagoon.
About half the size of the Giant Otter and solitary, it is not well known.

The Marine Otter Lontra felina, here off the Isla de Chiloé, southern Chile,
is rare and is also poorly understood. It is quite different from the
Sea Otter of North America.

There are fish-eating reptiles, most notably crocodilians, all of which eat a lot of fish; some eat little or nothing else.

Yacaré Caiman Caiman yacare with substantial fish lunch, Pantanal.

And there are even some fish-eating invertebrates, from sea anemones to insects such as giant water bugs and dragonfly larvae, to spiders. The genus of big fishing spiders, Dolomedes, is found across the world. The long-legged spiders run across the water surface where they seize and deliver a venomous bite to fish and invertebrates.

Fishing spiders in Yasuní NP, Ecuadorian Amazonia above,
and southern Sarawak, Malaysian Borneo, below.

If you like fish, you're not alone. Hopefully this post might have offered you a broader perspective on the fish dinner.

Ringed Kingfisher Megaceryle torquata with fish, Pantanal.

NEXT POSTING THURSDAY 15 JULY

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Cairns Centenary Lakes and Flecker Botanic Gardens; a tropical haven

Winter has come in Canberra and, while mild by the standards of much of the Northern Hemisphere, it's cold enough to get me thinking fondly of the tropics. I've written about Cairns before, focussing on the wonderful and justly famed Esplanade - see here - but today I'm writing about our other favourite part of this beautifully situated (but tourist-swollen) north Queensland city.

This is a sprawling 320 hectare site, with quite a bit of remnant vegetation, in the suburb of Edge Hill and at the foot of Mount Whitfield, just five minutes drive from the city centre. The definition of it is highly confusing and has changed over time. There are two entirely different elements to it. The formal gardens cover 38ha and most people think of them as the Flecker Gardens. To the south across Collins Avenue is the Centenary Lakes precinct. Officially the whole area is the Flecker Botanic Gardens; to avoid more confusion than already exists the formal gardens are now generally known simply as the Cairns Botanic Gardens and the rest of it as the Centenary Lakes.

A typical view of the Centenary Lakes; this is Freshwater Lake,
unimaginatively but unambiguously named. It was originally a three hectare ephemeral
swamp but was converted to a permanent lake in 1975.

The history stretches back to within a decade of the founding of Cairns in the 1870s. Botanist and horticulturalist Eugene Fitzalan founded a small formal public garden and nursery within the boundaries of the modern gardens. He was very well-regarded, worked with von Mueller, and has at least nine plant species named for him. However the modern gardens owe their name to Dr Hugo Flecker, a prominent radiotherapist, toxicologist and natural historian. He identified the source of mysterious deaths of swimmers as a box jellyfish, which was named Chironex fleckeri for him just before his death in 1957. He founded the North Queensland Naturalists' Club in 1932 and guided it as both a scientific and amateur body for the next 25 years. His story is a fascinating one and it's worth reading more about him here. The gardens were named for him in 1971, and some time later (I cannot find a date but the Centenary Lakes opened in 1976, so it could well have been then) the name was extended to the whole complex. 

It might be useful to have an idea of their layout for the account which follows; here's a basic map which should help.

It's a bit fuzzy, but I've added some yellow numbers to help with key features. 1; in the top left corner,
is the relatively small Cairns Botanic Gardens, rough rectangle bounded by the four obvious roads.
2; Saltwater Creek, a tidal creek which connects to the sea a short distance away.
3; Rainforest Boardwalk, an excellent introduction to the lakes area, via original swampy forest.
4; Freshwater Lake, a wonderful spot for water birds. 5; mangroves, which follow Saltwater Creek.
Courtesy Cairns Regional Council.

 

My interest is primarily in the Centenary Lakes system - you can see from the map how densely vegetated it is and most of this is remnant original forest. The formal gardens are just that - very pleasant but mostly of non-Australian plantings, and usually very busy with tourists. Still worth visiting while you're there of course, but I'm only going to feature one aspect of it today.

The Rainforest Boardwalk is our favourite way to approach the Centenary Lakes, though the picnic facilities and lakes are also easily accessed from Greenslopes Road at the bottom of the map.

The enticing western entry to the boardwalk. The fan palm leaves here
are metal!

The walk begins in palm forest, dominated by Alexander Palms Archontophoenix alexandrae; here the forest floor is wet but not generally flooded. This habitat has been almost totally eliminated in the Cairns area.

Alexander Palms dominating the palm forest, above and below.

The foliage of other trees, notably Blue Quandong Elaeocarpus angustifolius,
can be seen here also.

The clusters of small red palm fruits attract many birds (and bats by night), among which the noisy gregarious Metallic Starlings Aplonis metallica are most conspicuous.

Metallic Starlings (adult below, streaky immature, not very clear, above).

From here we move into Lowland Paperbark Forest, magnificently dominated by huge Giant Paperbarks Melaleuca leucadendra, some of them centuries old.

Giant Paperbark.

Lastly, with water lying on the surface of the ground, we enter Pandanus Swamp Forest, where Pandanus solmslaubachii rules with wet feet. 

The very distinctive foliage of pandanus.

The presence of Climbing Swamp Fern Stenochlaena palustris is also
diagnostic of the swamp forest.

Once we emerge from the forest we soon find ourselves on the banks of the Freshwater Lake where waterbirds are abundant, especially in the dry season. Some can be readily found down south...

Male Australasian Darter Anhinga novaehollandiae surrounded by Pacific Black Ducks
Anas superciliosa. Both are common and widespread, but shouldn't be ignored for that.

... others not so readily.

Magpie Geese Anseranas semipalmata, are strange goose-like waterfowl comprising their own
family. Common across tropical Australia (and southern New Guinea) but greatly diminished
elsewhere in Australia.

 

I think that Radjah Shelducks Radjah radjah (long known here as Burdekin Ducks)
are among the most beautiful ducks in the world.

 

Part of the flock, with Pacific Black Ducks.

 

And this was a real surprise when we visited the tropics in the summer
wet season a couple of years ago. Spotted Whistling Ducks Dendrocygna guttata are
found from the Philippines to New Guinea, and in the last couple of decades
have established a colony at Weipa up on Cape York Peninsula.
We'd not expected to see them in Cairns, some 800km to the south-east!
And it had been a while since I'd seen a new bird in Australia.

Other species can pop up anywhere in the gardens; these are all fairly common in Darwin but may be less familiar to you.

Black Butcherbirds Melloria quoyi have a most beautifully rich melodious call. They are now
placed in their own genus, away from the other butcherbirds.

Brush Turkeys Alectura lathami are found anywhere in the area, building their big incubating
mounds wherever it suits them.

Australasian Figbirds Sphecotheres vieilloti (here the northern yellow race)
are found anywhere there are figs (which is pretty well anywhere in this
part of the world). 

Helmeted Friarbirds Philemon buceroides are big noisy honeyeaters,
likewise widespread across the north.

Not seen nearly so often (partly for reasons this photo makes clear) is the
nocturnal Papuan Frogmouth Podargus papuensis. As well as New Guinea it is found
in Queensland down to nearly Townsville. We saw a pair, heavily camouflaged,
roosting in the mangroves by Saltwater Lake.

There will certainly be mammals present, but we've not been there at night. Here are a couple of others we came across; some you can't miss.

Krefft's Turtles Emydura krefftii are among those you can't miss - there's a healthy population
in Freshwater Lake, which come out to sun when things are quiet.

Skinks of course are abundant and diverse.
This is a female or non-breeding male Red-throated Rainbow Skink Carlia rubrigularis.
(Thanks to Steve Holliday for the id.)

Shining Oak-blue Arhopala micale. This is one of a group of butterflies whose
larvae are tended by ants as they feed; the ants provide protection and in turn 'milk'
the larvae for sugary secretions.

Orange-clawed Fiddler Crabs Uca coarctata along Saltwater Creek. They are found along most
of the Queensland coast in muddy shallows. These males are using their ridiculously enlarged
right claws to signal their dominance over other males and attractiveness for females.
They are useless for feeding, which is done by the much smaller left claw. The constant
movement of this claw, transferring food particles to the mouth, apparently reminded
someone of a fiddler's bow; apparently...

Not an animal (or a plant) of course, but I couldn't leave this impressive fungus out.

Basket fungus; at least I'm calling it that in the absence of better information
but it doesn't really resemble the Illeodictyon species which I know and are
usually known as baskets. Any help welcomed and acknowledged!

Finally, I mentioned earlier a part of the formal Cairns Botanic Gardens which I'll include here because of the particular presence of native animal species. This, perhaps surprisingly, is the impressive conservatory. 

Steamy and green, all that a tropical conservatory could be, and full of animal
life as well. It's a lovely experience.

The plantings in it are far from all native, but they attract an array of butterflies and even at least one attractive little snake. I imagine that the butterflies (all local species) have been introduced to the glasshouse, but they could leave if they wish, so I imagine there is some coming and going. 

 

Red Lacewing Cethosia cydippe, above and below.

Red Lacewings feed on a couple of species of rainforest vine.

Male Cruiser Vendula arsinoe. They are found from Queensland to
the islands to the north.

Female Cruisers lay their eggs not on the leaves of the native passionfruit which
is their host plant, but on nearby dead material on which they are less conspicuous.

The eggflies are a group of some 25 species of the genus Hypolimnas whose name purportedly refers to the 'egg' spots on the males' wings. It could well be true, and I've no better explanation.

Blue-banded Eggfly Hypolimnas alimena (on my trousers, inexplicably -
though I was doubtless sweating). It is found from Indonesia to NSW.

Varied Eggfly Hyplimnas bolina. They have a huge natural range from
Madagascar across Asia to northern Australia.

This skink had also taken up residence in the greenhouse; so far I've not
been able to put a name to it. Any assistance welcomed.

But the most surprising encounter there made us start momentarily, though it's quite harmless to humans. Not all the visitors were quite so sanguine however.

This elegant little Green Tree Snake Dendrelaphis punctulatus was gliding through
the undergrowth, paying no attention to us, though it climbs as well as its name suggests.
The skink, plus any geckoes and frogs present, are definitely at risk from it.

I hope that you can make it to the Australian tropics sometime soon in these difficult times; we're certainly aiming to be in north Queensland later this year (with fingers firmly crossed), and will spend a couple of days in Cairns. And while there we will certainly pay yet another visit to the Flecker Gardens. The visit wouldn't be complete otherwise. Maybe see you there?

NEXT POSTING THURSDAY 24 JUNE
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