That Bird Blog – Bird Care and History for Pet Birds

Bird extinctions, especially those on islands, are usually caused by introduced mammalian predators – most often cats and rats – and hunting. The sad story of the virtual disappearance of all birds from Guam is unique in that a reptile, the Brown Tree Snake, is at its root.

The Brown Tree Snake arrived on Guam in the late 1940’s as a stowaway (from the Admiralty Islands) in supplies used to repair the damages wrought by World War II. Finding a paradise of ample food and no predators, populations of this unusually adaptable snake soon exploded. Today 8 of Guam’s 12 forest dwelling bird species are extinct, 2 survive only in captivity or semi-captivity, and 2 are on the brink of extinction.

The Guam Rail, Gallirallus owstoni, became extinct in the wild in 1987. In 1984, while working at the Bronx Zoo, I received several pairs from a group held in captivity on Guam. They were amazingly aggressive little birds, and bred readily. Today they thrive in zoos and have been released onto Guam’s neighboring island, Rota. The Micronesian Kingfisher, Halcyon cinnamomina, also holds on in captivity but is gone from the wild. These have proven more difficult than the rails – those I worked with fed well but remained edgy and usually failed to breed. Captives that do reproduce often make poor parents, and hand rearing of the chicks is sometimes necessary.

The bird extinctions have wrecked havoc on the ecology of local forests. Nearly 70% of Guam’s trees rely upon birds for seed dispersal or to aid in germination by removing seed coats via the action of their digestive systems. Recent tests reveal that all seeds of most trees on Guam fall directly below the parent, where lack of sunlight and high levels of seed-predators condemns them to certain death.

Lacking birds, the snakes have now turned their attention to fruit bats, rodents, shrews and lizards, with catastrophic consequences – Guam’s endemic fruit bat and 5 lizards species are gone, and introduced house mice and rats are the only rodents observed in recent years. People have been bitten while sleeping (it is theorized that the snakes strike at rapid eye movements – how’s that for a “rude awakening”!?) and bird owners sometimes find a stuffed snake in a cage that formerly held their pet.

The birds of mainland USA are not without problems – nearly 25% of our species are considered to be at risk, and the recent introduction of Burmese Pythons to south Florida does not bode well for birds there.

The Brown Tree Snake is considered a potential threat to Hawaii’s unique and already fragile bird populations as well. Read more about this story at:
http://query.nytimes.com/gst/fullpage.html?res=9E0CE7D61239F937A25754C0A964958260&sec=&spon=&pagewanted=2

Guam Rail image is referenced from Wikipedia Commons at http://en.wikipedia.org/wiki/Image:Guam_rail.gif and originally posted by Sabine’s Sunbird

Brown Tree Snake Image is referenced from Wikipedia Commons at http://en.wikipedia.org/wiki/Image:Brown_tree_snake_Boiga_irregularis_USGS_Photograph.sized.jpg and was originally posted by Onionhound

Looking much like out-sized crows, to which they are related, Common Ravens are considered by many ornithologists (biologists who study birds) to be the most intelligent of the world’s 9,000+ bird species. People have apparently held this view from the earliest of times, as the folktales and legends of many races are filled with tales attributing great powers and cunning ways to these impressive birds.

We now have many indications of just how smart birds can be – a number use tools, and some have adjusted to changing conditions and have passed along their newly-acquired knowledge to other birds (more on that in future articles, but please write in if you’d like details). And, of course, parrot owners can fill volumes with tales of their birds’ learning abilities.

One of the most startling observations I’ve run across involved Ravens. One winter not long ago, people ice-fishing in northern Europe (I believe it was in Finland) began to find their hooks, devoid of bait and fish, lying on the ice near the hole that had been cut to allow access to the water below (fishing on an ice-covered lake during Finland’s winter is a cold business to say the least, so the lines were left untended while the fisherman wisely defrosted in nearby huts).

At first, neighboring fishermen were blamed, but some spying uncovered the real culprits. Ravens, apparently after watching people bait their hooks, learned to lift the lines with their beaks.

Keep in mind first that the birds had to associate the end of the line, now well below water, with food. The lines were quite long but, amazingly, the Ravens learned to stand on the slack each time it was laid down on the ice, so that it would not slide back into the water – and they figured this all out in the time that people were warming up and not watching!

The bait-thieves were likely helped in their efforts by the cooperative bond that develops between paired Ravens. Those observing the birds noted that one always kept watch while the other hauled up the line. As Ravens sometimes feed together, without posting a sentry, one is tempted to wonder – did they “know” to expect trouble?!

I once kept an injured Fish Crow (Corvus ossifragus), relative of the Raven, for a time. The bird took all of 20 minutes to learn how to open the latch on his cage’s door. Once I secured the latch with a lock, he would check the lock (once only) by rattling it, and no longer bothered with the latch itself. When I purposely left the lock unfastened, he immediately flipped it off and then lifted the latch.

Parrot owners are always great resources when it comes to “smart bird” stories.

You can learn a great deal about Raven natural history at:
http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Common_Raven_dtl.html

Image referenced from Wikipedia, uploaded by Franco Atirador in Feb. 2007, and using the GNU Free Documentation License. http://en.wikipedia.org/wiki/Image:Raven_croak.jpg

Many know the sad story of the extinction of the USA’s only native breeding parrot, the Carolina Parakeet, Conuropsis carolinensis.  The last known specimen of this species died in 1918, in the Cincinnati Zoo.  However, a spectacular, pigeon-sized parrot once frequented the mountains of southern Arizona and New Mexico, gorging on pine cones before migrating south to breed.

Last observed in the USA around 1935, the Thick-Billed Parrot ranged from Mexico to Venezuela, but is now largely confined to the Sierra Madre Occidental Mountains in northern Mexico.  Brilliant green with a bright red forehead and wing curve, Thick-Billed Parrots dwell at elevations up to 11,500 feet above sea level, and often forage in snow-covered trees.

Pine tree seeds are their main food – so much so that breeding is timed to their availability – and it is for this resource that flocks of over 1,000 foraged for several months each year in our southwestern mountain ranges.  Journal entries of naturalists of the time reflect the shock experienced upon encountering a thousand large, gaudy “tropical-looking” parrots in the snows high in the mountains of Arizona.  Thick-Billed Parrots also rely heavily upon acorns, and take other seeds, fruits, vegetables and insects as well.

Now drastically reduced in numbers, Thick-Billed Parrots are the subject of a zoo-based Species Survival Plan – a cooperative breeding effort seeking to ensure their survival, and are kept in private aviculture as well.  NYC’s Queens Zoo has a nice group in a large, outdoor exhibit – their raucous calls and constant activity render them among the most popular of exhibits.

The USA, especially Florida, is now home to a number of introduced parrot species, many of which breed here (please see my article on Monk Parrots).

You can read about conservation efforts for wild Thick-Billed Parrots in Mexico at:
http://www.worldtwitch.com/thick-billed_parrot.htm

Image referenced from one taken by LTshears in Wikipedia Commons.

August 1, 2008 – researchers working at the University of California (San Francisco) released the heartening news that they had identified the virus that causes Proventricular Dilation Disease (PDD), which has, since its emergence in the 1970’s, remained untreatable.  PDD has caused the deaths of wild and captive parrots of over 50 species, as well as birds in 5 other avian orders.  Aviculturists and conservationists consider it a major threat, especially to critically endangered species such as the Spix Macaw (of which less than 100 remain).

The virus, named Avian Bornavirus, is related to those that cause encephalitis in livestock, and attacks the nervous system.  Infected birds are unable to swallow, digest food or maintain their balance, and eventually die.

A test that enables technicians to positively identify the virus has also been developed.  Birds afflicted with PDD are often misdiagnosed, due the overlap of the symptoms with a number of other diseases.  It is believed that the test will assist in monitoring and limiting the spread of PDD, an extremely important step given that a cure still eludes us.

A veterinary journal article detailing a PDD outbreak in a parrot breeding center in Israel is posted at:
http://www.isrvma.org/article/61_1_3.pdf

Image referenced from Wikipedia Commons: http://en.wikipedia.org/wiki/Image:Spixara.jpg

The Greater Racket-Tailed Drongo, a conspicuous black bird with a deeply forked tail, often forages in flocks comprised of up to a dozen different species of birds.  The drongo perches above the flock, snatching insects that they disturb, and keeping an eye out for predators that might go unnoticed by its hunting flock-mates.  The associated bird species seek out drongos, apparently relying upon them heavily for protection.  Drongos feed more effectively when in such flocks, so the benefits go both ways.

Recent studies in Sri Lanka have revealed that, upon sighting a predator, a drongo will imitate the alarm calls of at least 4 other bird species (babblers, laughing thrushes, bulbuls and others), as well as the call given by the specific predator, i.e. a giant squirrel or eagle.

When unthreatened but hungry, the drongo will attract other birds to itself by imitating their calls – but this time it utilizes contact calls or mating calls.  It very effectively forms a small foraging group in this manner.  So, the drongo is not only choosing the calls of other species, but it’s using them in the correct context – hawk as opposed to snake, feeding as opposed to mobbing.  In essence, the bird is a true linguist.  When presented with a human intruder, one drongo improvised – after a very short “assessment” it gave forth the call of a Crested Serpent Eagle (perhaps because this is the largest predator it normally encounters?).

Male European Starlings, incidentally, mimic the calls of other birds in order to impress their mates.  An individual I visited often as a child, kept at the American Museum of Natural History in NYC, was able to imitate several words as well.

Some parrots seem to exhibit a quite detailed knowledge of what they are saying.

An abstract of an article dealing with research similar to that mentioned above is posted at:
http://scholarworks.umass.edu/dissertations/AAI3179876/

This image was originally posted to Flickr by Kai Hendry at http://flickr.com/photos/16105436@N00/99531708. It was reviewed on 09:53, 17 August 2007 (UTC) by FlickreviewR, and confirmed to be licensed under the terms of the cc-by-2.0.