Saturday, 30 August 2014

Saving the Fig Parrot

Brisbane has some beautiful coastal wetlands.  In large cities like Brisbane, the coastal wetlands are usually the last native ecosystems present that would be similar to how they were when the early settlers arrived.  The bush and rainforest have been transformed by weeds and have become an alien vegetation that is dominated by a handful of adaptable and aggressive species such as noisy minors that exclude other birds and animals.  Brisbane was a biodiversity hot spot but much has been lost.  Mangroves forests and salt pans which were once the poorest habitats for fauna have now become one of the richest as they are relatively immune to degradation.  Mangroves and the small islands of terrestrial forest they contain may even be the last habitat of some species.

Perhaps the rarest and most endangered bird in South East Queensland is Coxen’s Fig Parrot (Cyclopsitta diophthalma coxeni).  There are an estimated 100 individuals left but no one really knows as they are a cryptic species.  The small green parrots feed quietly on native rainforest figs and being the size and shape of fig leaves, they are very hard to see so targeted searches for this species usually fail to find any.  To save the species, the QLD and NSW State Governments want to start a captive breeding program, but nobody can find an occupied nest.  Stock for breeding programs is normally taken from wild nests.  I suppose that this would make my discovery of some possible old nesting hollows in a mangrove tree a significant find.

Cyclopsitta diophthalma coxeni
Possible old fig parrot nest holes in a mangrove beside the board walk at Nudgee Beach
A lizard in a stag beetle hole in the same tree.  The stag beetles may make pilot holes for the parrots.
Fig parrots make their own hollows.  Over about a month, they chew their way into a rotting branch.  Some hollows are about 60 cm deep which I discovered by finding fallen nest branches which split open when they landed.  If you find a fallen nest or any nest, be sure to report it to the national parks service.

Cyclopsitta diophthalma macleayana
Fig parrot in Cairns starting to tunnel - 17 July 2014.
fig parrot at nesting hole entrance
Stopping for a look around.
Cyclopsitta diophthalma macleayana
30 August, been sleeping in the hole for while now, but when there is a noise, the parrot comes to the entrance for a look (flash photo taken just after dark).
Cyclopsitta diophthalma macleayana
Female fig parrot begging for food from its mate.
Cyclopsitta diophthalma macleayana
Male fig parrot about to feed the female.
There is a species recovery plan for this species but it does not appear to address the nesting requirements for this species.  My knowledge of the subject comes from observing another subspecies of fig parrot, the red browed fig parrot (Cyclopsitta diophthalma macleayana) which is still common in Far North Queensland.  Fig parrots need rotting branches between 10 and 25 cm in diameter where the sapwood softens without the branch falling.   Live timber is too hard and in many cases would have unpleasant sap.  In nesting branches, often the sapwood rots away completely and the dead branch becomes an empty tube of bark when the parrot scrapes out the contents.  The favoured species are fig trees (F. drupacea) but I have seen nests in beach almonds (Terminalia arenicola).  I even have a nest near my house in a rainforest tree with one of the hardest scientific name I know of (Blepharocareya involucrigera).  Many of the nesting trees are in parks.  Twenty years ago, I would only see fig parrots flying in small groups high in the sky.  In only a few years, the fig parrots have moved into town.  I suspect many/most urban nests are lost to tree loppers who are called in to remove sick trees and dead branches.   If we can find places where trees can be allowed to old and decrepit, then every park fig in Brisbane City could one day be visited by this species.  Figs branches tend to rot until they become as light as foam before falling and if dead branches of suitable diameter were cut off a bit more than half a metre from living timber, the safety hazard from falling branches would be very small.  In fact many of the local nests around Cairns are in the stubs of branches that were trimmed by the city council.   Any branch with a gnawed hole or a gnawed test pit should be off-limits to tree trimmers.  The birds tend to chew out test pits until they find timber that just right.

Although I did find nest hollows in the mangroves, I do not believe that in general mangroves are suitable habitat.  Mangroves have high populations of rats which predate crabs and which would prey on parrot chicks as well.
Cyclopsitta diophthalma macleayana
Red browed fig parrot feeding on Ficus racemosa on an isolated tree on a sand ridge in the mangroves.
I suspect that another serious oversight of the recovery plan is that it does not address the food supply of the fig parrots.  Fig parrots eat green figs and not ripe figs. The northern fig parrots feed very heavily on Ficus racemosa and to a lesser extent on F. drupacea, both of which are native to Brisbane but which are rarely planted.  These figs are deciduous and drop very heavy crops of fruit a number of times a year so are not ideal park trees.   Planting these species around the margins of parks, particularly on the edges of the mangroves creeks and other places where people don’t typically venture might be a way of boosting food resources.  Fig parrots are highly mobile and isolated trees make up most of their food supply.  Another undocumented food is Melaleuca viridiflora flower buds.

Fig parrots feed for days to weeks on a single tree until fruiting stops and they return as soon as fruiting begins again, so isolated urban trees are likely to be extremely important to this species.  The species recovery plans should include the establishment a network of isolated trees which can fee the birds year round.  All the photos above were planted trees.  I planted them.

Tabbil-ban dhagun boardwalk at Boondall Wetlands
The 1.5 km long km board walk at Nudgee Beach is just across from Brisbane Airport - something to do before you catch a plane. 

Further Reading:
Coxens fig parrot Species Recovery Plan

Wednesday, 13 August 2014

Hovering Stilt Mangroves

There is an old question of whether stilt mangroves need to have a trunk running down to the ground or can survive held up by stilts alone.  On a recent trip up the Blind Barron, near Cairns, Australia, I found my answer.  The mangroves in this strange place appear to be walking over the mud until they fall like lemmings into the creek.  Some living mangroves are even defying gravity and are hovering over the water, supported entirely by no more than a few skinny stilts. 

Rhizophora (stilt) mangroves hovering over the creek
Going up the creek was like being in a tunnel with a fallen roof.  Stilt roots reached out over the creek from both side for almost 2 metres.  It was a case of going in on a very low tide to get under the overhanging stilt roots.  It is a creepy place and was famous for having a large crocodile.

Close to entrance of Blind Barron

The creek tapers quickly and becomes impassable by boat as the fallen trees block the way through. Normally creeks maintain their width with erosion on one site and regrowth of mangrove on the other.  I have never seen encroachment from both sides at once and this probably relates to the origin of this creek.

As far as boats will go

Sunday, 10 August 2014

How did Mangroves Evolve?

When I Google mangrove evolution all I find are a few pithy generic statements and no real information.  I think that if all the mangroves we currently have were to disappear, other plants would race to fill the ecological vacuum.  Next time you are in the mangroves, look for non-mangrove trees that are dipping their toes in saltwater.  It is surprising how many there are and how many species can actually survive in the edges of mangroves swamps, where they are surrounded on all sides by mangroves and are growing in mud.  The question is why are these species not completing the transition?  That is a very big question so lets investigate a small part of it, how mangrove stilt roots may have developed.

The one scientific paper on mangrove evolution that I could get for free (most are locked up behind science journal paywalls) was about the biogeography of mangrove evolution and it said that almost all the mangroves present today evolved in the Tethys Sea which was sort of where Arabia and India are today.  The earliest species were Acrostichum, the mangrove fern and Nypa, the mangrove palm.  These species like lower salinities so that is a clue.  The main mangrove species (Avicennia and Rhizophora) were around 50-70 million years ago so forests just like those lining the worlds tropical oceans today would have seen dinosaurs.  Perhaps the Tethys Sea was like the sea between Australia and the island of New Guinea is today.  The information from the paper tells me what evolved and where but does not tell me how the plants evolved.  If I knew how mangroves evolved, then perhaps I would be able to understand the barrier that is preventing more mangroves from evolving.

Recently I have been seeing stilt roots on some species of mangrove that normally do not have them.  These mangroves usually have pneumatophores which are breathing roots that protrude from the mud.  If the trees have a choice of stilt roots or pneumatophores, why do they choose pneumatophores?  Fortunately it is possible to collect evidence on conditions that favour stilt root development.

In a swale, which is a shallow valley between sand ridges, I found several white mangroves (Avicennia marina var. eucalyptifolia) with stilt roots instead of the usually pencil roots.  This is very strange as Avicennia is the champion producer of pneumatophores. The stilt roots are not as well developed as those of stilt mangroves (Rhizophora) but are clearly stilt roots none-the-less.  

Avicennia tree on stilt roots
Avicennia tree with stilt roots instead of pencil roots (pneumatophores)
The swale traps a pool of freshwater in the wet season and saltwater in the dry season.  I happened across the swale on one of the few days when it was completely dry.  During the wet season, the swale appears to be a window lake, which means that the freshwater table is above ground level.  Several large paperbarks live or lived among the mangroves.  However as sea level rises by a few millimetres each year and the drainage line to the sea expands due to tidal and storm water flows, the ingress of seawater is increasing and the paperbarks are declining. 

Mangroves growing around a paperbark tree (Melaleuca leucadendra
Two days later a full moon brought in one of the highest tides of the year and flooded the swale and covered the entire stilt root system of the Avicennia trees.  It seems that in the centre of the swale the water is just too deep for pneumatophores.  Avicennia on the margins of the swale grow thickets of pneumatophores.  

Mangrove swale with standing water at full depth

Stilt roots and a few pneumatophores when pool is full

Avicennia can also grow adventitious roots (roots growing from the trunk above ground level) in more exposed situations, such as river mouths, where regular tides are experienced. In these areas, however the adventitious roots rarely become stilt roots.

Adventitious roots on tree a creek mouth
Another mangrove species that can also form stilts instead of pneumatophores is the black mangrove (Lumnitizera racemosa).  Normally, black mangroves have very few pneumatophores unless they are in areas with freshwater seepage, then they grow strange root loops.   In one special place, near Pormpuraaw in the Gulf of Carpentaria, I found a forest where black mangroves have stilt roots instead.  The Gulf has only one high tide per day, whereas the east coast of Australia has two high tides each day.  There is much less tidal exchange of water and the headwaters of rivers probably remain brackish longer than their east coast equivalents.  Upstream of the tidal creek is a vast flat swampy plain that slowly drains into the mangroves for several months a year, creating freshwater tides for part of the year. It is these special conditions which create this strange forest.
Lumnitzera mangroves in headwaters of a creek which has strong seasonal freshwater flows
Lumnitzera on stilts with super long Avicennia pneumatophores
Brackish water swamps with still pools of water do not foster stilt roots, in these places pneumatophore development goes crazy.  In a back swamp close to the black mangroves is a brackish water swamp with pools of water surrounded by mangroves and reeds.  The mangrove pneumatophores are exceptionally long and dense.
Avicennia around a brackish pool with Baumea reeds
The Avicennia pneumatophores are as dense as the reeds
So my concluding conjecture is that stilts seem develop more in areas with seasonal freshwater flooding or tides.  In fact this is just the type of place that the forest mangrove grows.  The forest mangrove (Carallia brachiata) is the only non-mangrove member of the stilt mangrove family in Australia. Carallia has a propensity to grow masses of adventitious roots even when it is in rainforest on wet foot hills, so perhaps the stilt mangrove families propensity for this type of root structure combined with an opportunity is what lead to stilt mangroves.  

Monday, 4 August 2014

Life in a Beach

Each area of coastline is different.  It is not a case of the same species be present is slightly different numbers, each place seems to be the product of different ecological rules.  Sandy beaches are normally somewhere where animals are very scarce, perhaps only a few ghost crabs are present.  However the beach at Archer Point, close to Cooktown, is literally crawling with life.

Amphipod burrows
Amphipod burrows near high tide line

Amphipod about 1 cm long.
An amphipod

I have never seen a beach covered with burrows all the way from the low tide mark to the high tide mark before.  I even had to dig up the ground to find out who was in the burrows.  Amphipods jumped out of the first handful of sand so must be just below the surface.

Amphipods are basically a small (1 cm long) prawn-like animal that walks on land.  They have very big eyes and are nocturnal.  When chased, they can jump like crazy to avoid being caught.

Since seeing the amphipods at Archer Point, I have kept my eyes open and have scanned several beaches which seem similar in terms of protection and sand properties.  Finding amphipods on these other beaches is a struggle.  Normally, there are a few amphipods under washed up leaf litter and seaweed.  It is unusual to find large numbers on a beach that is almost clear of plant debris.  I suspect that there is freshwater seepage concealed within the beach which some how helps the amphipods.

Recently 4WD vehicles were allowed back on many Queensland beaches.  Scientific research had shown that vehicles driving on the beach crush many of the animals that live in the sand and hurt the ecology of the beach. My position on this matter is that each place has to be assessed individually.  It is nice to be able to pull up right beside the sea and relax and I would not like to see every beach fenced off.  Many beaches are reworked so much by wind and waves that few living animals are present and driving on these beaches does little damage.  However it is repulsive to find tyre tracks all over remote beaches where people should be able to enjoy freedom from such things.  In this case, there is no reason to drive on the beach at Archer Point as the beach is only 300 m long and has an unusual ecology featuring vast number of amphipods which would suffer due to vehicles on the beach.

There is no point in driving onto this beach as it is so short, yet lots of people do it
Amphipod holes beside tyre tracks