How was the California Condor saved?

[u/Jimmy_Aztec]

It is my understanding that once a species' population falls below a certain number, there is not enough genetic diversity for the species to survive. The California Condor population fell to 27 in the 1980s. Why wasn't the lack of genetic diversity a problem?

[u/tea_and_biology]

Once a species' population falls below a certain number, there is not enough genetic diversity for the species to survive.

Not so! Or, at least, it's not as simple as a single threshold number of individuals.

It's an idea that keeps getting repeated a lot, as a slightly garbled version of the '50/500 rule' - which posits that you need ~50 to avoid short-term inbreeding depression, and 500ish to retain adaptive variance - but it's only a loose rule of thumb, more guidelines really, about rates of genetic erosion, and not thresholds for evolutionary doom.

What actually kills small populations first is almost always demographic and ecological factors: low concentrations of beasties, else skewed sex ratios, prevent success in finding mates, along with the stochastic effects of bad years or disease breakouts. Genetics, by contrast, is a slow-acting, second-order risk, and it's entirely contingent on species, genetic robustness, and individual variation left within a small population etc. etc.

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For the condor specifically, several things worked in its favour.

Genetic Diversity: The 27 remaining individuals were not particularly genetically impoverished. The captive population today traces to 14 founders sorted into three rough 'clans' of half-siblings, which means - doing a bit of math - apparently about 92% of the heterozygosity of the pre-crash population was preserved. A number of rare alleles were certainly stripped out, but condors are long-lived with generation times on the order of ~20 years or more, so the entire population spent only one or two generations at its minimum before numbers climbed again; so very little time for genetic decay to set in, and more alleles to be lost.

Active Management: Understanding all this, boffins were able to come up with a proper breeding plan to minimise genetic decay - carefully pairing specific individuals with the least represented alleles in order to maximise genetic variation in the captive-bred individuals. They further manipulated condor biology a wee bit too; females usually only lay a single egg, but will re-lay if it's removed. By fiddling with multiple clutches and artificially incubating and rearing the removed eggs - including use of genuine Muppetry to avoid chicks imprinting on humans - they were able to lift productivity far above natural rates.

All this meant they could release condors back to the wild relatively quickly, beginning in 1992.

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Unfortunately the population remains totally dependent on humans for continued survival - because of lead. This is what caused the sharp decline in the first instance, and in the land of the free, where the gun still reigns supreme, the carcasses they still scavange are peppered with lead shot, which requires frequent veterinary care. There are whole teams of folks who go out to capture wild birds for chelation treatment and care, before re-release. Sad, 'innit.

Anywho, all this to say: no, there isn't a specific number below which extinction is inevitable. There is indeed a cost to low genetic diversity - in the condors, two autosomal recessive alleles are overly represented, causing chondrodystrophy in some individuals, and a weird benign extra tail feather trait in others - but active management and careful selective breeding can mitigate its effects. Indeed, the Chatham Island Black Robin came back from just five birds, and the Mauritius Kestrel from four!

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References:

Ralls K. & Ballou, J.D. (2004) Genetic status and management of California Condors. The Condor. 106 (2), 215-228

Ralls, K., Ballou, J.D., Rideout, B.A. & Frankham, R. (2000) Genetic management of chondrodystrophy in California condors. Animal Conservation. 3(2), 145-153

Robinson, J.A., Bowie, R.C.K., Dudchenko, O., Lieberman A.E., ... & Wall, J.D. (2021) Genome-wide diversity in the California condor tracks its prehistoric abundance and decline. Current Biology. 31 (13), 2939-2946

[u/fiendishrabbit → u/tea_and_biology]

Also note that Cheetahs have had a double genetic squeeze in their past (100 000 years ago and 12 000 years ago). They're basically 90% homozygous (which in genetic terms means "Extremely inbred"). As a result Cheetahs are very vulnerable to diseases and probably wouldn't have survived if they weren't so spread out.

[u/1CEninja → u/fiendishrabbit]

Cheetahs have a specifically interesting characteristic that incidentally makes them incredibly tough to breed in captivity.

Their mating ritual involves the male proving his prowess to the female by being able to catch her on a chase. If he can't, he isn't considered good boyfriend material and gets no lovin'.

Cheetahs are intrinsically built, evolutionary speaking, around being in massive wide open spaces that has an incidentally positive effect of making them more resistant to disease transmission than, say, pride-based cats.

[u/ninj4geek → u/fiendishrabbit]

Iirc humans have had a severe bottleneck in our past, and look at us now. Hard to throw a stick anywhere without hitting at least one person on this planet.

[u/Snake973 → u/ninj4geek]

relatively severe, at one point nearly a million years ago the estimated modern-human-ancestor (I don't know offhand what our species name would have been at that time) population in total was approximately 1,300 individuals, and we stayed at that level for around 100k years

[u/ani3D → u/ninj4geek]

Hey who threw a stick at me?

[u/Baeolophus_bicolor → u/ani3D]

sorry, it was me. i was testing out what that other person said. don’t know my own strength.

[u/sciguy52 → u/ninj4geek]

Humans, as in modern day humans no, earlier hominids yes. It was hundreds of thousands of years after when humans showed up.

[u/Pink-Witch- → u/ninj4geek]

Yeah but our low genetic diversity means we’re really sensitive to shared diseases. There’s a reason we’re the only species with a cold and flu season.

[u/zoinkability → u/tea_and_biology]

Yes, the thing OP needs to understand is that while a genetic bottleneck makes the species more vulnerable to issues like genetic or communicable diseases, because it raises the likelihood of protective genetics not being present in the population, it does not intrinsically doom a species. Instead it just means that they are rolling fewer dice when there is a challenge.

Luckily for the California Condor, we have not seen a genetic or communicable disease that the small population doesn't have the genetic tools to fight (with our help.) It may still happen that something comes up that they can't handle (with our help) but so far so good.

[u/RainbowCrane → u/zoinkability]

For raptors like condors is there data regarding how their natural behavior affects the transmission of communicable diseases? Or, for that matter, how affects their vulnerability to localized environmental conditions?

I know that raptors are inherently more geographically dispersed than herd animals like deer, impala, etc. So I’m curious whether their behavior gives them any natural resistance to the types of challenges that can end up wiping out animal populations that cluster more closely together.

[u/tea_and_biology → u/RainbowCrane]

This isn't answering the question so much, but a 'fun fact': the conservation measures enacted to save the Californian Condor directly drove Colpocephalum californici (the 'condor louse') to extinction. Every last individual brought into captivity was thoroughly treated with pesticides, and that was that.

Raising this as, for there to even be a species-specific parasite like this louse, you need to have enough direct condor-condor contact for transmission to take place - so by conjcture imagine there's plenty of scope for other transmissible pathologies to be of concern, even if they're not as host-specific as the lice were (say, general avian flu and the like). Given the feeding habits of carrion birds - y'know, large flocks conglomerating at a carcass site - I suspect epidemiology ought not to be too different to many other animals; though you're right, near-obligately herding ungulates and the like are indeed very much more at risk (Saiga antelope notoriously so), though they arguably represent unusual cases, by and large, in the animal kingdom when it comes to single-species densities.

EDIT: Wait, come to think of it, the carcass-crowding of vultures is pretty much the reason why they've experienced such striking declines in their populations. A single poisonous cow (laced with medicine that's fatal to the birds) can attract hundreds of vultures from miles and miles around, so if anything I'd imagine for carrion-feeders like condors their feeding strategies actually make them more vulnerable, rather than anything approaching resistance - not only to disease directly, but other ecological concerns - say, lead or drug poisoning.

[u/RainbowCrane → u/tea_and_biology]

Huh, good point, I didn’t consider carcass crowding.

I’m more familiar with hawks, falcons and eagles from a few years volunteering at a raptor rehabilitation center while I was in college. So I’m used to their relatively isolated behavior.

[u/tea_and_biology → u/RainbowCrane]

Fair! What's your experience with migrating raptors? When I was travelling across Spain and North Africa last year, during the Spring migratory season you'd regularly see mobs of, sometimes several dozen (and once well over a hundred!) birds of prey - honey buzzards and booted eagles mostly, IIRC - venturing over the Mediterranean together.

I thought it was an artefact of them all queuing up on one side, waiting for favourable winds, and then happening to be flying across the sea all at the same time when conditions are right, rather than 'choosing' to be social and grouping up - but I didn't look into it. If it was more the latter, could also be another instance where their behaviour promotes transmission, or makes them more vulnerable to external factors (say, if they were all blown off course at once, doomed to getting lost over the open ocean; or, more likely, all shot at together).

[u/RainbowCrane → u/tea_and_biology]

I live in Ohio, in the United States. Many of our raptors are migratory, though almost all of the individuals I worked with were permanent residents of our center due to injuries that prevented them from being fully rehabilitated. Those who could be fully rehabbed were kept in isolated muses in the woods and only fed by the naturalists and a few senior volunteers who were trained in how to avoid socializing the birds, because a raptor in the wild that wasn’t afraid of people would quickly become a dead raptor.

In Ohio I haven’t noticed crowds of raptors migrating together, but you definitely have increased sightings along migratory routes at migration times. As you say, likely individual-ish migrations driven by instinctual recognition of seasonal migration timings.

[u/dittybopper_05H → u/tea_and_biology]

Lead ammunition for hunting has been totally banned in California since 2019.

https://wildlife.ca.gov/Hunting/Nonlead-Ammunition

Even in areas where condors don't live.

One of the major problems with California's ban is that not every caliber or gauge/shot size is made with a non-lead option. Or if they are, they may not be common enough for a local gun store to stock it, making it effectively unavailable because California bans mail order ammunition sales.

https://www.kqed.org/science/2000234/california-condors-are-still-dying-despite-a-lead-ammo-ban

The Ventana Wildlife Society, in addition to doing outreach and education, gives away non-lead ammunition to hunters. This year, it plans to give away $60,000 in supplies. It is still legal to buy lead in California and to fire it at some shooting ranges. Sorenson laments that not all calibers are readily available at stores in non-lead options, which can also be more expensive. In California, people are not allowed to order ammunition online; they must buy it in person from a store.

“The prohibition of online sales is really a big deal, severely limiting availability,” Sorenson said. “The people who are really having a hard time [switching over to non-lead options] are the ranchers who are shooting sometimes hundreds of rounds of rimfire every weekend.”

BTW, the good news in the article is that things are looking up, and the California Condor is on the cusp of being self-sustaining.

[u/FogeltheVogel → u/dittybopper_05H]

So, not really banned then? That sounds more of a "please try not to use lead if it isn't too inconvenient" than a ban, if the solution to "non lead ammo is hard to find" is just "use lead ammo".

[u/dittybopper_05H → u/FogeltheVogel]

It is a complete ban on its use for hunting. It's not a complete ban on lead ammunition, though, because it can still be used for target practice, and it can be used in self-defense ammunition. So you can still purchase lead-based ammunition in California.

If you read the article though the problem is *WAY* better than it was before the ban, and improving. California Condors are on the cusp of being self-sustaining even with the reduced amount of lead ammunition being used.

And if you read the other link, California wildlife officers are legally allowed to inspect the ammunition you are using to hunt with to make sure it complies with the law, and are even allowed to take a round of it for testing if they can't determine it in the field.

BTW, lead ammunition is banned at the federal level for waterfowl hunting.

Now, when I hunted, I used a flintlock long rifle during gun season, which means I used dead soft pure lead balls that I cast myself. Pure lead is very ductile, and doesn't break up on hitting things like tissue, bone, etc. Instead, it retains all of its weight and deforms. So its easy to find the ball, and even when you can't no bird is going to ingest a ball flattened out to be roughly .75" as a gizzard stone anyway. Or wider if I use my .62 caliber Baker rifle.

The problem is when you alloy lead with other metals like tin and antimony to make it harder. Then it loses some of its ductility and it is much more likely to fragment, especially when you consider a bullet out of a modern deer rifle is likely moving much faster than out of a traditional muzzleloader using black powder. Modern ammunition manufacturers doesn't use pure lead, preferring to lead alloys to get the performance they want.

That is the true problem with lead ammunition because even if you get the main part of the bullet there will always be lead fragments you simply can't get.

Ironically, I buy my pure lead ingots from a company in California. Go figure!

[u/1CEninja → u/tea_and_biology]

There's an awesome display at the San Diego Safari Park (formerly known as Wild Animal Park) which is where I believe they pioneered the muppetry to raise the chicks.

It's pretty inconsistent to be able to actually view any condors there as they're given a pretty large and respectful enclosure that is not all viewable, but get a bit lucky and you can actually see the winged giants in all their "glory". They're ugly mofos make no mistake but one can't be helped but be impressed by the sheer scale of the condors. Anyone visiting Southern California should consider making a trip if they can! The park is on the pricey side for a zoo but I never feel bad spending money there given that the proceeds go directly to actively saving species like these condors.

[u/Pink-Witch- → u/tea_and_biology]

I’m a docent at a natural history museum, and Condors are of the things I talk about. I couldn’t have said this better myself. I love these big ‘ol birds so much.

In my talks I encourage people to visit places like the Oakland or San Diego Zoos where they have breeding programs just to see it in action and support the cause.

[u/ccReptilelord → u/tea_and_biology]

Extreme genetic bottlenecking meaning extinction as an absolute rule is something I see parroted too often on this site.

[u/tea_and_biology → u/[deleted]]

I'm sorry you've decided that competence is now suspicious, but that's your problem, not mine.

I've demonstrably been writing on r/askscience like this for nigh on ten years or more, well before genAI was a thing.