Magpie Mystery

May 2010

How can I unravel the puzzle of these strangely coloured birds?

Lately I have been seeing some birds with strange white patterns hanging out with the local magpies. These birds look like Magpies but have too much white on them. Can Australian Magpies (Cracticus tibicen) hybridise with other birds like the Pied Butcherbird (Cracticus nigrogularis)? Are these birds magpies and why do they look so different?

Answer

Heterochroistic Magpie The white belly on this female magpie from Marcoola is usually a tell-tale sign that you have a bird with a colour mutation rather than your average sub-species or hybrid.

How Interesting, the birds in your photographs are indeed Australian Magpies (Cracticus tibicen) but with a difference!

They have suffered a partial loss of black pigment (melanin) in their plumage, which means they are now ‘heterochroistic’. Heterochroism is a genetic colour abnormality which in this case has lead to asymmetrical patches of white plumage showing through where black plumage should normally exist. These birds are not albino. If they were the eyes, legs and beak would usually be pink or red, and the entire animal would be white instead of just patches.

Sadly because of their new “clothes”, these birds could be at a natural disadvantage and not live for long. Having plumage which stands out from the crowd can make a bird obvious to predators. They may also have weaker feathers due to a lack of melanin, and to top it off impaired eyesight.

This is a unique family group, the bird in the middle is the typical “black-backed” male, with the female on the right and on of the offspring on the left.

What is really fascinating about your birds is that this seems to be a family group with a ‘normal’ adult male, a ‘heterochroistic’ female and two ‘heterochroistic’ offspring. This means that seemingly normal coloured male bird would have also needed to carry the recessive gene for heterochroism, to pass the condition onto the young birds.

Not every strangely coloured looking Australian Magpie you see will be a ‘heterochroistic’ bird. While Australian Magpies and Pied Butcherbirds are closely related, often occuring side-by-side in suburban areas, these species are not known to hybridise. You would be much more likely to encounter one of the other seven documented subspecies of Australian Magpie (Cracticus tibicen) that occur in different parts of the country.  Each of these has slightly different plumage and in certain regions these subspecies can overlap and hybridise, just to make things more confusing.

Heterochroistic Magpie Birds such as this individual from Bribie Island have had a large amount of black pigment (melanin) removed from their plumage and could be in higher danger of predation because they stand out from the suurounding environment.

The one thing these subspecies and hybrids will always have in common is an all-black front, so this is why your birds are colour mutations. Sometimes it may not be this easy to separate a subspecies from a bird with a colour abnormality. If this is an area of interest for you it would be a good idea to research what subspecies and hybrids you may encounter while travelling, so you can tell the difference.

It will be a great opportunity to see how this family group progresses, if the young reach adulthood and to monitor your local flock for more of these birds over in future years. A fascinating result of nature.

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