Birds of (small) Prey

In my last post I included a photo of a cuckoo-shrike overpowering, after quite a struggle, a big phasmid (or stick insect). In terms of relative sizes of hunter and hunted it's probably the biggest invertebrate prey I've seen consumed, but it made me think of the unimaginable myriads of invertebrates, especially insects, that are consumed by birds around the world every single day.

Here's the picture in case you missed it; a dark-phase White-bellied Cuckoo-shrike Coracina papuensisstruggling to overcome a huge, and presumably pregnant female, phasmid. Nowra, New South Wales.

In this case the energy expended by the bird was considerable - I watched it struggling with the insect for at least 15 minutes - but the reward was very substantial and worth the effort. It would have found its lunch by searching the foliage of eucalypts for the camouflaged insects. Many birds hunt thus, gleaning leaves and branches for prey ranging in size from phasmids, cicadas and crickets to much smaller but more abundant fare.

Female Blue-crowned Trogon Trogon curucui, Muyuna Lodge on the Amazon River,
northern Peru. She has also captured a very large stick insect.

Yellow Wattlebird Anthochaera paradoxa with cicada, Bridport, Tasmania.
Cicadas are smaller than phasmids, probably with more hard indigestible bits,
but tend to be numerous.

However most invertebrates gleaned from foliage are much smaller; as long as these snacks are sufficiently numerous and easy to find, the effort of snapping them up is also rewarded. I am constantly amazed at the number of caterpillars and other larvae that are lurking (and munching) on trees, shrubs and understorey plants, given the number that are eaten daily by birds and the number of chewed leaves that are still in evidence! Here are some efficient caterpillar-eaters, each of which must find many food items of this size every day - and of course far more if they're feeding hungry nestlings.

Male Crimson Chat Epthianura tricolor, Great Victoria Desert, Western Australia.

Fire-eyed Diucon Xolmis pyrope, a tyrant flycatcher which specialises in living in the cold windy
expanses of Patagonia. This one was in Torres del Paine NP in southern Chile

Pallid Cuckoo Cacomantis pallidus, Great Victoria Desert; this caterpillar seems ridiculously small
for the size of the bird, but again there was probably a good supply of them.

Australasian Pipit Anthus novaeseelandiae near Canberra; I'm sure this beakful of caterpillars was
going to feed demanding babies.

Shining Bronze-Cuckoo Chrysococcyx lucidus, Uriarra Crossing on the Murrumbidgee River near Canberra.
That spring there was a major population explosion of these tiny furry caterpillars in the casuarinas along
the river, and many small cuckoos arrived to feed on them. Not many birds can manage
the often irritating caterpillar hairs but cuckoos seem to specialise in them.

Even smaller leaf-eating insects exist, and are also sought by many birds. Lerp is the term used for the larvae of many species of sap-sucking psyllids, which are true bugs (ie Hemipterans) that secrete surplus sugars to form waxy protective coatings. Many birds nip these off to access the insect inside. The most specific practitioners of this feeding method in Australia are the pardalotes, and on a still summer day the pattering of falling lerp covers can clearly be heard. Here are some honeyeaters which also feed on them, though each insect can only provide a tiny reward.

Fuscous Honeyeater Ptilotula fusca Jerrabomberra Wetlands, Canberra.
Hanging upside down is an effective way to access the underside of leaves.

Yellow-plumed Honeyeater Ptilotula ornata, Nundroo, far western South Australia.

Varied Honeyeater Gavicalis versicolor, Cairns Esplanade.
The white material on the underside of the fig leaf above the bird's bill is
probably webbing protecting either caterpillar or spider rather a lerp,
but the foraging strategy is the same.

Finally before moving on from gleaning here is a bird whose prey's identity I'm not certain of. The Crested Shrike-tit Falcunculus frontatus is a powerful-billed gleaner now regarded as the sole member of its family. Normally it rips bark from tree trunks to extract small animals lurking beneath it, but this one was tearing apart a silken 'bag' in Callitris pine woodland.

I suspect the bag contained processional caterpillars (generally well-protected by stinging hairs), but I couldn't confirm that.

Some birds specialise in catching insects in the air, while many others do it opportunistically. It requires great dexterity and skill.

Mixed flock of woodswallows (mostly White-browed and Masked) hunting flying
insects in front of a coming storm, central Queensland.

Dragonflies, though hard to catch, offer good rewards; they are an important part of the diet of Rainbow Bee-eaters Merops ornatus. This species and the next have long slim bills like forceps.

Rainbow Bee-eater with dragonfly, Namadgi National Park near Canberra.

Great Jacamar Jacamerops aureus with unidentified flying prey, Manu Biosphere Reserve, Peruvian Amazonia.

The Australian (and south-east Asian) fantails, Family Rhipiduridae, are mostly aerial specialists, but some species also chase prey along the ground with outstretched wings and tail, which both help with steering and flush insects from the ground.

Rufous Fantail Rhipidura rufifrons, Monga NP east of Canberra.

Grasshoppers, being abundant and often conspicuously moving on the ground, are common victims of perch-and-pounce hunters. Here are some 'late' grasshoppers.

Crimson Chat male, Great Victoria Desert, Western Australia.

Laughing Kookaburra Dacelo novaeguineae, Cape Hillsborough NP, Queensland.
This is a big bird, often claimed as the world's biggest kingfisher; the meal is appropriately large too!

Noisy Miner Manorina melanocephala, a common and pugnacious colonial honeyeater
which is primarily an insectivore, Callum Brae NR, Canberra.

Female White-browed Woodswallow Artamus superciliosus, Karumba, tropical Queensland.

And I think this Yellow (or Green) Oriole Oriolus flavocinctus is about to eat a beetle (despite being mostly a fruit-eater). but it could equally probably have taken it off the ground or gleaned it from foliage.

Yellow Oriole (now often referred to as Green Oriole to avoid claimed confusion with an unrelated and utterly
dissimilar bird from northern South America), Cairns, Queensland.

Other birds extract prey, often wood-boring larvae, especially of moths or beetles, from living or dead wood. Those with finer bills extract their meals from crevices in bark.

Narrow-billed Woodcreeper Lepidocolaptes angustirostris, Chapada dos Guimaraes, western Brazil.
This is one of a very large number of related species in the old South American ovenbird group;
it is clearly a rewarding lifestyle.

White-browed Treecreeper Climacteris affinis near Canberra. Another old Gondwanan,
but not at all related to the woodcreepers; a striking example of parallel evolution.

Grey-crowned Babbler Pomatostomus temporalis, Longreach Waterhole, 700k south of Darwin.
This one was assiduously probing holes in dead wood.

Species with stronger bills simply smash their way into the wood to get their wriggling rewards. Woodpeckers, found in all vegetated continents except Australia, are famed for this. Small holes excavated by these little woodpeckers are obvious in these photos.

Cinnamon Woodpecker Celeus loricatus, Rio Silanche north-west of Quito, Ecuador.

Yellow-fronted Woodpecker Melanerpes flavifrons near Sao Paulo, Brazil.

Bigger woodpeckers make a much bigger mess of the tree however!

Magellanic Woodpecker Campephilus magellanicus excavation, Torres del Paine NP, Chilean Patagonia.
This magnificent bird is up to 45cm long.

They're not the only birds however which demolish wood in the search for big grubs.

Yellow-tailed Black-Cockatoo Calyptorhynchus funereus, tearing a wattle sapling apart to
extract larvae, Murramarang NP, south coast NSW.

Some birds dig into the ground to get their rewards.

Laughing Kookaburra, Rosedale, NSW south coast, whose beak shows how far it has been probing into the soil for food.

Finally for today, while we tend to think of birds hunting in water as primarily interested in fish or frogs, many of them are interested in much smaller rewards and flocks of various waders extract many thousands of small animals from mud, sand and water daily. The principle is much the same whether they are probing into mud or water - they usually can't see what they're doing and rely totally on sensitive receptors in the tip of the bill and the inside of both upper and lower mandibles. These 'touch/taste' receptors (we have no equivalent) are packed in at densities of thousands per square millimetre. When a living organism is sensed (and they can distinguish between live food and inanimate objects) the bill snaps shut. While the moment of capture is beyond my means to photograph, and the prey is usually tiny, here are some practitioners going about their business.

Bar-tailed Godwit Limosa lapponica, Cairns. Note the upturned bill; there are numerous subtly or obviously
different bill shapes among waders to enable many species to feed in the same place while
minimising competition.

Black-necked Stilt Himantopus mexicanus, Galápagos.

Sanderling Calidris alba, also in the Galápagos; it has a much shorter stouter bill.

Immature White Ibis Threskiornis molucca above,
and Yellow-billed Spoonbills Platalea flavipes,
both at Jerrabomberra Wetlands, one of Canberra's premier birding spots.

Ibis and spoonbills are closely related, but while ibis probe into the mud, spoonbills
systematically sweep their bills from side to side in the water, snapping up tiny
organisms as they contact them.

Flamingos achieve the same result, but in a unique and seemingly improbable fashion, with their heads upside down!

American Flamingo Phoenicopterus ruber, Galápagos. This bird is straining the shallow water for
invertebrates (especially shrimps) and algae. Food is separated from water and unwanted items
using a large sensitive tongue with fleshy spines to pump water in and then out again,
sieving it as it goes. This species is found in the Galápagos and the Caribbean.

Crabs are abundant invertebrates in most shore situations, and feature in many birds' diets.

Common Sandpiper Actitis hypoleucos with crab snack, Darwin.

I recently observed a quite different bird enjoying a crustacean meal too, which took me quite by surprise. The light was wrong, but the subject makes it worth while.

Pied Currawong Strepera graculina, dismembering a freshly caught yabby (a common Australian freshwater crayfish),
Cotter River Reserve, near Canberra. I can't readily find other accounts of this.

Shellfish and other snails make a good meal, but require special techniques and strength to extract.

Young Dolphin Gull Leucophaeus scoresbii, Tierra del Fuego, far southern Argentina.
This bird seemed a bit unsure what to do next, but I've watched Kelp Gulls in Chile
repeatedly flying up and dropping heavy shells onto rocks until they broke, and
then extracting the flesh.

Snail Kites Rostrhamus sociabilis on the other hand know exactly what to do with the big Apple Snails
(Pomacea spp.) that comprise virtually their entire diet. The elaborately elongated
slender upper mandible evolved to extract the snail from its shell by cutting the columellar muscle
that attaches the body to the shell; once that is accomplished the snail simply drops out.

This bird was showing its skills in the Pantanal, south-western Brazil.

So, there's an invertebrate for virtually anyone - at least for representatives of just about any bird family you can think of. Apparent declines in insect populations reported from many parts of the world are cause for concern for this reason, as well as many others. Meantime we can just wonder at the largely hidden vast diversity of small life on which millions of birds depend, and at the myriad of strategies developed to this end. It's still a wonderful world.

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Perito Moreno; a rare growing glacier

Perito Moreno Glacier is one of the chief attractions for visitors to Argentinian Patagonia, and quite justifiably so. It lies in the eastern fall of the Andes, some 60km west (in a straight line) of the touristy town of El Calafate, on the shores of Lago Argentino. This is a vast lake, extending all the way from El Calafate (and well beyond) to the glacier; it was 'discovered' (ie by Europeans) by Francisco 'Perito' Moreno, a nineteenth century Argentinian archaeologist, anthropologist and explorer of Patagonia. 'Perito' means an expert, and has a similar connotation to 'professor' as we might apply it respectfully to a learned person.  

The north face of Perito Moreno Glacier from approximately six kilometres away, across Lago Argentino.

The glacier lies within the huge Los Glaciares National Park, which covers some 700,000 hectares of Andean wilderness, including much of the Southern Patagonian Ice Field, the world's largest after Antarctica and Greenland. (An ice field is defined as a complex of glaciers which buries much of a mountain range.) To give a sense of scale to the photo above, the ice wall we can see towers more than 70 metres above the water surface (with another 100 metres of ice below it). The glacier arises 30 kilometres deeper into the mountains, and the final wall of ice (not all of which is visible in this shot) is five kilometres wide. 

Location of Perito Moreno, near to the Chilean border (which is within the Andes).

The map, taken from Google Earth, shows part of the ice field, the foot of the glacier (at the end of the red arrow),
Lago Argentino, El Calafate, and the approximate point from which the first photo was taken (at the yellow diamond).

This map shows too how the southern arm of the lake is cut off by the glacier pressing against the opposite shore of the lake; the water rises in the southern arm, fed by local runoff, until it is many metres above the level of the rest of the lake. Eventually (on average every five years or so) it breaks through dramatically; this aerial photo was taken on 21 March 2016, which was only three weeks after the most recent rupture. I am surmising that the pale colour of the arm is because it is normally shallower than the main body of water, but I'm open to more informed suggestions.

A closer shot of the glacier wall from the same location as the photo above.
The southern arm of the lake is in the foreground with the main lake out of sight beyond the glacier.

The first time I visited Perito Moreno, more than 10 years ago, I joined one of the daily trips which cross the lake, and conducts walks on the glacier - closely supervised by very well-informed guides, certainly on that occasion.

The boat which conveyed us - the dents in the bow were food for thought!

The ice wall becomes more impressive as the boat approaches it.

The blue in the ice develops as snow falls on the ice and is compressed by later falls, until air bubbles are squeezed out and crystals grow; ice with small crystals and air bubbles appears white. This blue was one of the things that delighted me that day - it was the first glacier I'd ever seen! Here are some images from then.

The glacier's edge, as we approached it.

Ice cave.

The view back to the lake, from atop the glacier.

Glaciers carve out landscapes, and move vast quantities of earth and rock across the surface, and the walk enabled us to see the impacts of that.

Gouges in the rock left exposed when the glacier retreats in summer; the bottom of the glacier
acts like a huge coarse sheet of sandpaper.

 

Moraine is material moved, perhaps for tens of kilometres, under the glacier and left behind when
the ice seasonally retreats. This is terminal moraine, ie at the end of the glacier.

As suggested in the post heading, Perito Moreno is most unusual in this worryingly warming world, in that it appears to be defying trends and logic, and expanding. Since the glaciologists can't agree how to explain it, I'm afraid I won't be trying to!

That was a fascinating experience, and I enjoyed it, but overall I think I prefer the walk that follows the lake shore, on a raised board walk, looking across to the glacier wall.

The glacier face; in the left foreground is the point where the southern arm of the lake (to the left) breaks through.

What is very obvious is the raft of broken ice in the water at the base of the glacier - and of course that is where it originates. 

From closer, the scale yet again becomes evident; many of the pieces of floating ice are huge.

The glacier is a slow river of ice, and at the foot ice is constantly breaking off as it it pushed by the millions of tonnes of ice behind it.

You've got to be lucky and patient to observe the moment of calving, and I was a touch too slow
to get the best of this one.

The results however are very easy to observe as they start their long journey across the lake to eventual oblivion; and some of those results are very odd indeed!

Some very singular icebergs, in which it is not hard to find animal-like shapes!

The surrounding forests are beautiful old-growth Nothofagus, or southern beech, forests, with a startling similarity to such forests in Tasmania and New Zealand - as well they might, having their origins in Gondwana when such forests stretched from a united Australia and New Zealand through Antarctica to South America - and of course were carried across the world when the continents ripped asunder. 

Old growth Nothofagus forests, above and below, straight out of ancient Gondwana...

Apart from the beeches themselves - and Nothofagus species are found in those Australian and New Zealand cool temperate rainforests - other plants are familiar too. 

Winters Bark Drimys winteri, Family Winteraceae.
This is regarded as one of the most ancient of living flowering plant families, offering an insight into
how early flowering plants may have looked. Very similar plants in Australia were until recent decades
also called Drimys, but are now known as Tasmannia.

Gavilea araucana, a member of an orchid genus of some 15 species, mostly found in the cold
far south of South America.

Close-up of the lovely flower.

Animals are present, but the busy and not always respectful hordes of tourists keep them at bay. There are always some treats however.

Patagonian Grey Fox Lycalopex griseus near the foot of the glacier.

A day in wild Patagonia would not be complete without a condor, and Perito Moreno rarely disappoints.

Andean Condor Vultur gryphus soaring against the mountains;
the snow drifts create a somewhat surreal effect.

But the highlight of my most recent visit was a much smaller predatory bird, who would probably have preferred to be overlooked...

Austral Pygmy Owl Glaucidium nana.This little owl, no more than 20cm high, hunts in a range of habitats
in the south of the continent, taking prey (mostly birds) up to twice its own size.
It is often active during the day; this one was by a busy track.

Most of my time in Patagonia has been in Chile, but my two visits to Perito Moreno stand out as highlights of my time in the wild south. Consider finding out for yourself.

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