Spreading the Seeds; animals 'helping' plants

I was reading an intriguing story yesterday - which I'll get to shortly - which led me to think about animals being 'employed' by plants to distribute seeds. There are various ways of doing this, including by sticky burrs which cling to fur and feathers, eventually being dropped (or releasing the seed) some distance from the start of the journey. 

Bidgee Widgee burrs, Acaena novaezelandiae, Family Rosaceae, hitching a ride on my boot laces,
alpine zone, Kosciuszko National Park. They'd probably prefer a wombat or wallaby, but I'll do!
Daisies are another family to employ this strategy.

Australia has perhaps the richest ant fauna in the world, so it is unsurprising that plants from a wide range of Australian families have employed them to assist in distributing seeds. Obviously they don't want the ants to break the seeds up and eat them, and in fact the seeds are usually too hard for the ants to eat. Instead the plant attaches a nutritious temptation to the seed, which the ants haul off to the nest, detaching the seed when they get there and leaving it on the surface or in an underground garbage dump. This dry attachment is either an aril (if it derives from the seed attachment) or an elaiosome (a fatty body different from the aril), and is smaller than the seed. Ants have been observed carrying such seeds up to 75 metres from where they found them.

Discarded seeds surrounding an ant nest, near Alice Springs, central Australia.

But does it work? It certainly does!

Seedlings sprouting from ant nest, Great Sandy Desert, Western Australia.

Ants don't seem to pay much attention to colour, so these arils and elaiosomes tend to be pale in colour. However some acacias have colourful (especially red) arils, which are displayed high on the plant for birds to gather - again taking the seeds along with it.

Blackwood Wattle Acacia melanoxylon, pods, Namadgi NP, near Canberra.

Overall however the simplest and most effective strategy is to have the seeds eaten by a large mobile animal and discarded elsewhere, in droppings or perhaps as regurgitate. Energy is a very important resource - and temptation - for animals, which of course is why so many plants wrap their seeds in colourful, sugar-filled fruits, constructed from the wall of the fertilised ovary. The hard seed passes through the body, deposited sometimes many kilometres away. Here are some birds caught in the act!

Double-eyed Fig Parrot Cyclopsitta diophthalma eating figs (of course), Cairns Esplanade, Queensland.

Metallic Starlings Aplonis metallica eating palm fruit, Cairns Botanic Gardens, Queensland.

Silvereye Zosterops lateralis, with heath berries, Family Ericaceae (or Epacridaceae),
Australian National Botanic Gardens, Canberra.

Pied Currawong Strepera graculina eating Cotoneaster sp. berries, suburban Canberra.
These hedges (and related Pyrocantha spp.) are widely planted in older Canberra suburbs, and currawongs
are important distributors of the seeds into nearby nature reserves, where they are a serious weed hazard.

Male Mistletoebird Dicaeum hirundicum with mistletoe seed, Bundjalung NP, New South Wales north coast.
Mistletoebirds live almost exclusively on mistletoe berries, and are the major vector of the seeds.
It is a fascinating story, and will have its own post one day.

In rainforests in particular, birds and fruit bats are very important vectors of the whole forests' seeds - trees, lianas and shrubs. 

Rose-crowned Fruit Dove Ptilinopus regina in fig, Kakadu NP, Northern Territory.
Other key bird groups involved in distributing rainforest seeds in Australia include bowerbirds
and orioles (which include the figbirds).

Another important contributor is Australia's second-largest bird.

Southern Cassowary Casuarius casuarius, Atherton Tableland, northern Queensland.

We now know that the seeds of the Javan Ash Ryparosa kurrangii, a rainforest tree from north Queensland, germinate far better if they've passed through a cassowary. In fact, over 90% of seeds taken from cassowary droppings germinated, compared with only 4% of uneaten seeds. It has long been known that cassowaries are important vectors of rainforest seeds, but this adds another dimension to their value in the rainforest ecosystem. (The researchers also incidentally found that Javan Ash seeds have one of the highest levels of cyanogens ever recorded in a plant, but presumably the birds pass them through quickly enough and without breaking the surface of the seed, so that they are unaffected.)

In rainforests elsewhere in the world, other birds perform similar roles.

Yellow-throated (or Black-mandibled) Toucan Ramphastos ambiguus, with cecropia fruit,
Wild Sumaco Lodge, northern Ecuador.

Grass-green Tanager Chlorornis riefferii, Abra Patricia Lodge, northern Peru.

Red-crowned Barbet Psilopogon rafflesii, Bako NP, Sarawak.

Bats must never be underestimated however, despite doing their valuable work under cover of darkness.

Black Fruit Bats Pteropus alecto, Charters Towers, Queensland.
Big bats like this - with wing spans of more than a metre - travel many kilometres in a night,
visiting distant rainforest remnants. Smaller seeds are ingested, but even larger ones can be carried
for several minutes before being spat out.

They are not the only mammals to perform the task however.

Ecuadorian Squirrel Monkey Saimiri macrodon (or Saimiri sciureus macrodon), Yasuní NP, Ecuador.

Seedlings sprouting from elephant dropping, Kibale NP, Uganda.

Some plants have even secondarily 'invented' fruit by causing the stem immediately below the bare terminal seed to swell, turn red or black, and fill with sugars, for the same reason as other plants develop 'real' fruit.

Dwarf Ballart Exocarpos strictus.The red 'fruit' is the pedicel, or flower stem, the real fruit is the hard dark nut below it,
comprising a seed in a hard casing.

Mountain Plum Pine Podocarpus lawrencei, Namadgi NP near Canberra.
This is a conifer, so clearly cannot have true fruit (which, as explained earlier, must develop from a flower).
Again the pedicel is swollen, coloured and sweet, and the seed sits on top of it.

Which is pretty much the story - except that I mentioned at the start something I read which triggered this. It was a study conducted by Japanese ecologists which implied that at least one group of animals might have adopted a similar strategy to distribute their 'seeds' - which are really eggs. Stick insects, or phasmids, are poor distributors - many are flightless - but occur on many islands. 

Titan Stick Insect Acrophylla titan, Nowra, south coast NSW.
This one can grow to 25cm long.

Moreover, many species can reproduce parthogenetically - ie without mating. In this case all the hatchlings are female; if they mate both males and females result. The scientists presumably wondered about these two things, because they tried feeding eggs of three phasmid species to Brown-eared Bulbuls Hypsipetes amaurotis, a major phasmid predator in Japan. Up to 20% of the eggs survived, and some hatched, meaning that the birds could potentially be enabling the flightless insects to island-hop. Their next task is to compare the genetics of stick insects along known bird flight paths, to see if there is a correlation. A small thing, but surely much of life depends on a collation of small interesting things...

White-bellied Cuckooshrike Coracina papuensis with large (probably gravid female) phasmid, Nowra.
Did this bird do a favour to its lunch by sparing and spreading its eggs?

NEXT POSTING THURSDAY 14 JUNE

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Wagga Wagga Botanic Gardens

On a recent family-related visit to the inland city of Wagga Wagga I spent some time in the very pleasant native plants section of their impressive botanic gardens, set on the lower slopes of forested Willans Hill. I knew then that I needed to share the discovery with you, as part of my sporadic series on Australian native plant-oriented botanic gardens, especially regional ones. (You can find more under the 'botanic gardens' Label to the right of this panel.)

A general panoramic view of part of the gardens.

Wagga Wagga (you'll get into trouble with locals if you try saying just one Wagga!) is New South Wales' largest inland city, with well over 50,000 people, set on the Murrumbidgee River in the remnant woodlands of the dry south-west slopes region. It is prosperous and always busy, so the gardens are something of a haven, as gardens are.

You can find Wagga Wagga at the end of the red arrow above.

Their story began in the 1950s, when the City Council and the New South Wales Soil Conservation Service began remediating on old gravel quarry by contouring the site and planting thousands of trees, mostly native. Early in the following decade a plan for a botanic gardens was prepared, with the first plantings in 1962; it opened in 1969. The native gardens, along with a big rose garden, were part of the original plans, perhaps unusual for the time. Other specialty gardens feature camelias, cacti, proteas, water saving techniques and a Shakespearian garden, as well as a little zoo and a miniature railway, but I'll leave you to discover those for yourself. The overall area is some 20 hectares, of which I estimate that some 3-4 hectares comprise the native section, at the northern end of the complex.

The entrance to the native plants section.
As you can see from the previous photo the section comprises a mix of garden beds and lawns,
with many mature trees, mostly eucalypts.

The plantings are quite eclectic, being drawn from widely across the continent, and labelling is minimal, which can lead to some frustration if you have a mind like mine which likes to put names onto things. Accordingly I can't name all the photos which follow, and any assistance from you would be greatly appreciated. It is particularly difficult with the eucalypts - Australia has nearly 900 of them, so without knowledge of their place of origin, an amateur such as I hasn't much of a hope.

Here are a few of the trees, starting with some that I do recognise (not many eucalypts in this category!), progressing to a couple that I might know, and ending with one about which I have no idea! A plant is none the less beautiful for lack of a name of course.

Red-flowering Gum Corymbia (formerly Eucalyptus) ficifolia, a bloodwood with distinctive fruit
and foliage (the species name means 'fig-leafed).
A lovely small eucalypt, widely planted but restricted to a very small natural distribution near
Albany in south-western Australia.

Hoop Pine Araucaria cunninghamii, a rainforest tree from the east coast of Australia, from
the Macleay River to Cape York and into New Guinea. More about its family here.

Firewheel Tree Stenocarpus sinuatus, another east coast rainforest tree,
this one in the Proteaceae family.

I think this lovely euc is Sugar Gum, E. cladocalyx, another widely-planted species with a small natural
range, scattered in South Australia in the southern Flinders Ranges, on Eyre Peninsula and Kangaroo Island.

I'm guessing Wallangarra White Gum E. scoparia for this one, but with less confidence.
It too has a very small natural range, on the mountainous border of south-east Queensland and NSW,
but is a popular planting .

And a very attractive eucalypt about which I have no clue at all - any suggestions welcomed!

The garden beds are generally well-tended, though one has some large clumps of what is presumably intended to be Swamp Foxtail Cenchrus purpurascens (also known as Pennisetum alopecuroides). I have some concerns with this for a couple of reasons. One is that there is uncertainty about whether it really is a native grass, and other members of the genus (from Africa, Asia and South America) are highly invasive weeds. Moreover one authority I've consulted is pretty sure that this is another Cenchrus, which means that is an invasive weed; KayePea suggests C. setaceus. I think that prudence would mean removing this planting. (My thanks to KayePea, below, and my friend and weed expert Geoff Butler for assisting with this issue.)

If my authority is right about these they could well take over this bed (and beyond).

Most beds are weed-free however.

A massed planting of a pigface, probably Carpobrotus sp.

Fern-leafed Grevillea G. pteridifolia, a magnificent sight in flower, found across northern Australia.

A guinea flower, Hibbertia sp, family Dillenaceae; the genus has some 150 species from across the country.

I'm pretty confident this is Pink Pavonia, P. hastata, family Malvaceae.
It was long thought to be native to the Australian inland, but is now believed to have
established itself here, having been introduced from central South America.

And of course there were birds present, as there weren't many people around when I was there. Unsurprisingly many of these were familiar and common urban species.

Young Willie Wagtail Rhipidura leucophrys, surely one of Australia's favourite birds,
bold and curious and found across the entire continent.

Male Australian Magpie Gymnorhina tibicen, another ubiquitous species.

Yellow-rumped Thornbill Acanthiza chrysorrhoa, another widespread species, though small
and often overlooked despite feeding on the ground in flocks.

Crested Pigeon Ocyphaps lophotes sunbathing on a lovely autumn day. I think this is one of the world's
most attractive pigeons; it too is found in much of Australia and in recent decades has been spreading south-east.

Others were a little less common, especially in suburbia.

Immature Fan-tailed Cuckoo Cacomantis flabelliformis; this bird, though relatively large,
was probably raised by either the thornbills or Superb Fairywrens which also live in the gardens.

Double-barred Finch Taeniopygia bichenovii, a little delight which certainly
seems to be declining around Canberra at least.

I was surprised at the number of exotic Common Blackbirds Turdus merula present (though the combination of open space and understorey suits them well); however while I was there their numbers decreased by one! Nothing to do with me, but this deadly Brown Goshawk Accipiter fasciatus, flew over me as I sat on a bench with lunch still struggling in its claws, then perched in cover for a while before taking its meal elsewhere.

I can't promise that sort of drama on each visit, but you won't know until you try! I'm sure you won't regret an hour or so spent there however.

And I've just discovered there's a rainforest gully tucked away there too (in Wagga Wagga?!). Oh well, I'll just have to go back again I guess. Maybe I'll see you there.

NEXT POSTING THURSDAY 31 MAY

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For My Melbourne Readers!

Next Thursday (24 May), I'll be chatting with Andrew Robertson of Hill of Content Bookshop about my recent book Birds in Their Habitats; journeys with a naturalist, and I'd love it if you could come along, and let others know who might be interested.

This is a Free Event but please RSVP to melbourne@hillofcontentbookshop.com
or phone 03 9662 9472

I do hope I can meet some of you there!

NEXT POSTING THURSDAY 17 MAY.

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Gannets and Boobies; formidable fishers

Gannets and boobies form a Family of 10 distinctive large seabirds, now known to be most closely related to the cormorants and darters. They are strikingly handsome birds, and dramatic to watch, as they hurtle headlong into the water from high above it (mostly from between 10 and 30 metres up, but in the case of Masked Boobies this may be as much as 100 metres). They close their wings as they hit it (at speeds of up to 100kph, according to Bryan Nelson's classic The Gannet) and continue to chase the fish or squid beneath it. This chase can take them as far as 25 metres beneath the surface; fish are usually swallowed before they resurface. This latter strategy is useful for avoiding the thieves - frigatebirds, gulls, skuas - which are lurking above with intent to steal the rewards of their skill and labour.

Blue-footed Boobies Sula nebouxii fishing, Puerto Vilamil, Isla Isabela, Galápagos, above and below.
You can see the streamlined shape they adopt just before hitting the water.
This was a spectacular sight, right in the harbour.

'Gannet' is based on the same Old English word root as 'gander', which at that stage simply meant a goose, with no implication of gender; for reasons uncertain it came to be applied to the Northern Gannet, which in northern Scotland is still referred to as 'Solway Goose'. The general usage of the word didn't occur until the 19th century. 'Booby' was used in the sense of a 'foolish fellow' - presumably for sitting trustingly in colonies in the face of marauding sailors. We really are shameless! The gannet genus Morus means the same thing, from the same Greek word which gave rise to 'moron'. If I were a gannet (or booby) I'd be suing...

It was long believed that they were closely related to pelicans, but that is no longer the case; pelicans are closer to herons and ibis. The gannets and boobies share the Order Sulidae with frigatebirds, as well as cormorants and darters. (From Sulidae comes the world sulid, referring to a member of the family; I will use it here, not to be smart but because it's easier than saying 'gannets and boobies' each time!) One characteristic that they share with pelicans, which contributed to the misunderstanding, is having all four toes connected by webbing for better swimming power. It seems however that they and the pelicans evolved this adaptation independently.

Blue-footed Booby feet (as if you couldn't have guessed!), Puerto Ayora, Galápagos.
The hind toe has been dragged around to the side to enable the more extensive area of webbing.
In ducks and gulls, for instance, only the front three toes are joined.

The plunging lifestyle inevitably requires other adaptations too.

Nazca Booby pair Sula granti, Española, Galápagos.
The eyes are set right alongside the bill, enabling binocular vision, which is most unusual in birds.
They seem to choose the prey from high up and adjust their dive as come down to follow it, which of course
requires very accurate depth perception. Moreover in a vigorous headlong dive, external nostrils would
be a serious hazard, so they have been dispensed with them; instead they open inside the bill.

A less obvious adaptation is in the breast, which is cushioned to protect internal organs by a remarkably developed set of air-sacs (bronchial extensions which spread throughout the body of a bird to enable their unique respiratory system), like bubble wrap. Their neck muscles are unusually strong, they have membranes to protect the eyes, and a layer of spongy bone at the base of the bill to absorb the impact.

The sulid bill has small serrations to assist in handling fish; on the other hand it lacks the hooked tip of many other large fishing birds.

Red-footed Booby Sula sula, Genovesa, Galápagos.
You can see the serrations here if you click on the photo to enlarge it.

Within the family many (but not all) authorities recognise three genera. The oldest seems to be the Abbott's Booby Papasula abbotti of Christmas Island and surrounding oceans, which apparently split from the ancestors of the other species some 22 million years ago. The ancestral gannets and other boobies parted company 17 million years ago. Despite this the differences between the two groups are not particularly striking. The six Sula boobies are essentially tropical and subtropical, while the larger three Morus gannets are mostly birds of temperate seas. The boobies are generally darker (though as with the Nazca Boobies above there are exceptions). Gannets are white (except for wings and tail) with yellowish heads.

Australasian Gannet Morus serrator, south coast New South Wales.
These long narrow pointed wings are typical of the family.

Here are a couple more examples of these very elegant wings.

Masked Booby Sula dactylatra, Muttonbird Point, Lord Howe Island.

Nazca Boobies, Galápagos.

Peruvian Boobies Sula variegata, Islas Balasteros, Peru.

A further difference lies in the sex size ratios; female boobies are notably bigger than their males, but this is not the case with gannets.

Most sulids are completely white beneath, presumably to provide camouflage from predators coming from beneath them in the ocean. However there are two exceptions; the Brown Booby Sula leucogaster, found throughout most of the world's tropical oceans, and some Red-footed Boobies... This strange latter statement is based on the fact that Red-footed Boobies come in two basic morphs, a brown (shown above) and a white - plus variations on those themes!

Brown Booby, Lady Elliot Island, Queensland.
Even here the belly is white.

All sulids nest in colonies, though this is presumably mostly due to necessity - suitable island sites are not easy to find. The size of the colony and the breeding area will also determine how densely packed the colony is.

Nazca Booby colony at sunset, San Cristóbal, Galápagos.

Masked Booby colony, Lord Howe Island.

Cape Gannet colony Morus capensis, Lambert Bay, South Africa.
This is an extraordinary experience; the huge colony comes right up to a viewing hide.

All these species nest on the ground - in most situations there is no choice, and the gannets in particular are large birds. The nest is no more than a scrape on the ground.

Nazca Booby nest scrape.

This nesting Masked Booby on Lord Howe Island seems to have prepared even a scrape among the grasses.

 However Red-footed Boobies, the smallest sulids, nest in shrubs and trees.

Red-footed Booby colony, Genovesa, Galápagos.
Most Galápagos Red-foots are brown morphs...

... but not all! This is a white morph Red-footed Booby, with an egg.

At first sight, this looks like the brooding strategy of most birds, but sulids lack brood pouches (featherless areas of the belly which have blood vessels close to the surface for warming eggs and chicks) - perhaps they would cause too much heat loss in the water. This parent - they both take turns at brooding - is covering the egg with its feet under the body. These feet have many blood vessels, which warm the egg. On the other hand the bird is basically standing on the egg, so it must have a particularly thick shell!

Nazca Booby and egg, Genovesa.

Most sulids lay only one egg, though Blue-footed and Peruvian Boobies breeding in the great anchoveta grounds of the Humboldt Current lay two or three and aim to raise them all. In other cases, where two eggs are laid (ie Brown and Masked Boobies) the second is simply insurance against loss of the first, and the second chick always dies.

The two eggs of this Nazca Booby on Genovesa represent a most unusual situation for this species,
but they would certainly not have resulted in two fledged chicks.

For the first few days of the chick's life it is brooded on the warming feet, beneath the parents' bodies.

Nazca Booby with young chick on feet, Genovesa.

Here are some more chicks at increasing ages; ages cited are of course approximate. Except where specified, all photos were taken at different colonies on Genovesa.

Nazca Booby with one week old chick, just growing down feathers.

Nazca Booby and 2-3 week old chick.

Red-footed Booby chicks, 2-3 weeks.

Nazca Booby feeding 3-4 week old chick, growing but still quite helpless.

Blue-footed Booby and 3-4 week old chick, North Seymour, Galápagos.

By now the parents may start to leave the chick on its own, as it is now able to adequately manage its body temperature, while both parents forage. However fledging in most species takes around 15 weeks - and this is after some six weeks of egg incubation!

Red-footed Booby chick losing the last of its baby down.

Red-footed Booby chick, now fledged, practising flapping its wings in preparation for
its first flight lesson.

But even after fledging the youngster will depend on its parents for food for another few weeks; it presumably takes this long to learn the complexities of the plunge-diving feeding system.

This relaxed approach to breeding means less stress on the parents, a strategy which is made possible by their longevity, which may be 20 or more years. They may not start breeding until six years old.

Displays, both for reinforcing pair bonds, and for defending territories in crowded colonies, are highly ritualised. Famously, Blue-footed Boobies flaunt their feet, presenting them overtly when landing, and performing slow dances featuring the feet, lifted for inspection. As in most animal blue bits, the effect is a trick, utilising bubbles in cells stacked in precise ways to reflect blue light; more on that here. However Blue-footed Boobies' feet aren't just blue - they cunningly brighten them up by incorporating yellow carotenoids to form the most sought-after shades, which are bright aquamarine. (Mind you, when I started to look up this colour on line I found many shades all called aquamarine, so I'm no wiser as to which is the optimal Blue-footed Booby foot.) Birds with feet artificially dulled by experimenters lost their attraction to their mates. And there was a real correlation between foot colour and fitness. Here are a couple of very different shades I've seen in Blue-footed feet.

Puerto Ayora, Galápagos.

Pucusana, Peru.

And that is probably enough for today, though I've greatly enjoyed preparing this tribute to the wonderful sulids; I hope you've enjoyed it too. Here are just a couple more images...

Peruvian Boobies, Islas Balasteros.

Masked Booby preening, Lord Howe Island.

NEXT POSTING THURSDAY 17 MAY.

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