No. of finches required to sustain a viable genetic pool.

[Lonchura]

What is the minimum number of birds required to sustain a viable genetic pool, of pure wild strain finches, before defects/mutations appear in the following generations? I recently read an article in the Queensland Finch Society newsletter ‘Finch News’ (“A Sincere Apology” by Kent Smith, January.2011.p.12), in which his breeding wild form true to head colour Gouldian’s was starting to show mutations much to his disappointment.

I myself have been working on Australian Native Bush Budgies and the original captive pool of birds was very limited. I have been aware of the potential for mutations happening for many years. So I have been purchasing new bloodlines (birds) from around the country furthermore, I have also been keeping records of my budgies to avoid interbreeding. I was unsure of the genetic history of the original budgies and the additions I have bought from other breeders over the years (I was assured they were all quality true to form budgies). Now after eight years of working to keep them in their wild Green form, I am starting to get some mutations showing up. But … lucky for me I have been banding and keeping fairly accurate genetic records of my birds (using a software program called ‘Bird Tracker’) and I have been able to back track my records to try to weed out possible mutations or splits.

I see breeding true to wild form finches (or any other birds for that matter), eventually becoming a problem with all our birds in Australia if we as breeders are not very careful. A few examples that spring to mind are the Red-faced parrot finch (Erythrura psittacea), Java rice sparrows/finch (lonchura oryzivora) and African Silverbills (Lonchura cantans).

[nathan morley]

i agree Lonchura it is very hard to get pure normal finches an parrots these days couse all the finches and parrots like zebra finches , mannikans , budgies , cockatials etc... are all mutated or split an i think they look ugley so i onley keep normals .

[Diane]

The figures seem to vary wildly on this topic from the highly unlikely 1 pair for those with a Biblical view (Noah's Ark) to 160 pairs.
It seems like animals could just about get away with 80 pairs but would need some human intervention at some stage, but as a population, 160 pairs seems to be the number geneticists agree on.
However an American study in 2005 suggests that the Americas were populated with approximately 70 people, so maybe the figure of 80 pairs isn't that unlikely.

To me, the thing about putting a number on this raises all kinds of questions.

What if a larger than average number of the original pairs already carry a genetic mutation to begin with? Using this captive number the mutation could be concentrated and come out earlier than would be expected in the wild. In the wild any mutation that detracted from the species survival would quickly be wiped out.
Its already been established that most of us as humans have the capacity to be carriers of at least 5 to 10 genetic diseases in our DNA. As humans we have the ability to travel the planet and we can exist in multiple ranges of climate. Birds are more restricted in the areas they can inhabit and more susceptible to changes within that area.

As finch breeders we would be more than likely starting off with a captive group complete with their already introduced genetic problems.
So then the question is would this 160 pairs still be enough genetic diversity to overcome the mutation?

If we were able to source wild caught pairs, due to the birds only existing in certain geographical areas could you be sure of getting enough diversity to begin with?

Considering nature has made these birds exists in confined areas surely some mutations are needed to ensure the continued species survives?



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[Tiaris]

I think its very hard to put a number of pairs figure on it. More important is the genetic vigour and genetic variation of the remaining stocks. For example, a genetic pool of 20 pairs of Green Avadavats of which all young breeding age birds are closely related and have been showing signs of lack of genetic vigour for the previous 10 years or more. Compared to this just 10 pairs or less of another species with diverse features and from a range of genetic sources is a far more secure base to build a viable population from.
I often hear people say something to the effect that rabbits and sparrows established to huge numbers from a very small initial base stock so why can't a small number of rare finches do the same? Of course, the rabbit and sparrow started from small numbers from a genetically robust source population. If the small numbers of rare finches are the remnants of a long-term dwindling stock of birds which have become genetically closer over decades of decline this is not a fair comparison. If the rare finches came from an imported consignment from a free-breeding genetically diverse captive (or wild) population then the rabbit/sparrow comparison is a fairer one.

[E Orix]

This subject has been discussed for years and years
Most times it has been left to fizzle out which is a shame but probably the best for the birds.
The reason being that a blanket no inbreeding policy be the normal approach is the safest way.
This is not directed to line breeders etc as they are experienced and know what to do but if a statement came out inbreeding is not an issue
then virtually every begginer,backyard breeder wouldn't bother and brother/sister,mother/son father/daughter matings would be rife its bad enough now.
Hap hazard breeding methods are not good for the continued quality of stock,the experienced breeders should and do everything in their power to limit in breeding especially with our rarer species
Even Western Govt. have laws relating to people not having children when closely related
So should we not continue the approach inbreeding should be a last resort.

[west finch]

I think the sparrow theory works in the wild due to natural selection only the strong survive to breed any weak birds never last long enough to pass on there genetics . If any birds in a domestic breeding program where selected on vigour and then bloodlines the problem would not be as bad .Only a theory.

[SamDavis]

Some time ago I read the book "The Beak of the Finch", which describes a long term (20 years + if I recall) study of Darwin's finches on a small island in the Galapagos. If I recall correctly some of the species on the island virtually died out (less than 10) during an extended dry period. Once the rain came this species was able to rebuild its numbers suprisingly rapidly. From memory there was a small amount of hybridisation occuring between related species, however the characteristics of the individual species returned rapidly. I'll try and find my copy and locate some quotes relevant to this discussion.

[Lonchura]

I was also looking at the book "The Beak of the Finch" Friday night at the Queensland Finch Society meeting; it was what prompted me to think about the topic in more detail. I started to wonder about how it related to Australia’s dwindling finch populations. So I posted the question and obviously there are even new comers like young Nathan Morley who have also been thinking about the situation.
I have no issues with mutations being bred (in fact I keep them myself and do admire some of them for their colour), but I am concerned that everyone is thinking that somebody will still have the plain old inexpensive normal birds. Then when it’s realised there could be a problem with the genetic diversity and vigour of a species.

IT WILL BE TO LATE AGAIN!

It’s the again bit that worries me, as this situation has happened many times before but now I feel obligated to try and stop it happening with a species I know and have had experience with. I can’t help to save them all and you probably can’t either but you may be able to help by being part of a group to work on another species. One that is within your interest area, skills, price range and available time you may already have them in your collection.

It is near impossible and sometimes too late to find good unpolluted bloodlines for many finches kept in Australia. But this should not be an excuse for not trying to maintain what we have. I believe if someone doesn’t try and maintain true wild form (colour, size, shape and in some situations sub species) bloodlines, they will all be gone from Australian aviaries. It seems most finch breeders in Australia have forgotten or do not understand we have no resupply options for wild caught finches from within Australia or overseas. Keeping true to wild form finches will be impossible without the help of other dedicated breeders with similar beliefs. As we have identified there is no set number and the only thing all can agree on is the bigger the group of people maintaining reasonably accurate records of their different blood lines to maintain the genetic vigour and diversity to ultimately sustain all populations.

.

[GregH]

I like what you're trying to achieve but going back to your original question there isn't a single answer. I don't have any specific finch examples but in plants I've got a bit of an idea from my work. The number required to maintain a viable population isn't a single figure since you don't know how inbred a population is to start with unless you genotype them and you have no idea which deliterious genes are in that population and how resistant the species is to inbreeding. In a small population you can quickly eliminate deliterious genes and their combinations but the cost is genetic diversity which may be of benefit in other areas. Some species can sustain this if they are adapted to the conditions under which they are kept but change things then they're in trouble especially if they are supre specialised like pandas. In contrast some other species quickly succumb to inbreeding depression so you need to pay attention to pedigrees. It's an experimental science to find out which populations and which species are going to suffer from inbreeding depression.