Haast's Eagle

Last episode, we talked about the small side of birds, but today I want to go big.

Specifically, I want to take you back to the Pleistocene, which started 2.6 million years ago and continued until around 12,000 years ago.

This geological period is more commonly known as the Ice Age and featured a lot of animals that were larger than their counterparts seen today.

These were known as Megafourna, many of which were mammals, but in New Zealand however, the land previously free of mammals except bats.

The Megafourna were exclusively avian.

These megacise birds survived into the Holocene.

This is the period following the Pleistocene, which continues to this day before becoming extinct sometime within the last 700 years.

Are you intrigued?

If you like birds, if you like knowledge, well my friend you find yourself in the right place.

Welcome to Blooops, a podcast about birds.

Hi, I'm Matt, bird enthusiast from New Zealand.

Get ready for silly sounds, but serious facts. Let's get into it.

Now, if I were to ask you what super large extinct bird comes to mind when you think about New Zealand, I feel like it's a pretty safe bed that most people would say more.

But there were others, and one actually hunted and ate more.

It was the apex predator of its ecosystem.

Māori history, through both verbal accounts and rock wall art, tell of this great eagle, and is further supported by the fossil record with the first bones being discovered in 1871.

The excavation project that unearthed these remains was overseen by the director of the Canterbury Museum at the time Julius von Haast.

Hence, this bird went on to become known as Haast's eagle.

In all reality though, the person who found and identified these fragments as a previously underscribed species was the museum taxidermist Friedrich Fuller.

So full as eagle may have in fact been a more appropriate name.

Just a little side note, I know there's been a lot happening in the world of bird names, with a shift away from uponiness naming, i.e. being named after somebody.

This is for a few reasons which I won't get into today, and I fully support this change.

However, for this episode, I'll stick with calling our featured bird Haast's eagle, as this is what it's most commonly known as to my knowledge.

I was so glad though to learn its Māori names, Puakai and Tehokuori while researching.

Hopefully one day these traditional names will become the norm, as they have with other New Zealand birds.

For more information on the bird naming shift, I recommend listening to the Science of Birds podcast episode titled Avian Rebrand, new names for many North American birds.

Anyway, back to the episode. What even name it's given, this bird is the largest eagle ever known to exist.

The males will larger their males and are estimated to have weighed between 15 to 17.8 kgs and 11.5 to 12.3 kgs respectively.

For reference, the largest eagle alive today, the Harpe eagle, weighs around 9 kgs.

Now, a couple more things weren't mentioning, based on what we've discussed so far.

Firstly, fossils for this bird were initially discovered in Canterbury, which is located in the South Island of New Zealand.

This is important because interestingly, it seems that Haast's eagle only existed in the South Island, but not in the North Island.

Secondly, in the late 1860s, just prior to the discovery of these first fossils, so when few to no people, other than those that were indigenous to the land, knew of the eagle's existence.

There was a report of two large birds of prey being shot by a European explorer.

This occurred at Landsborough Valley, and they were labeled as being Australasian Harriers.

The crazy thing was that they were measured as being twice the normal size for an Australasian Harrier.

Could this have just been a measuring or recording mistake, or was this the location of the last Haast's eagle?

Haast's eagles. This identified due to a knowledge gap.

Unfortunately, I don't think we will ever truly know.

Due to its distinctiveness, Haast's eagle was originally placed in the genus Harpegonus.

All on its own, i.e. it was considered monotypic.

This means that it was thought to have no close relatives.

Recent genetic research, however, has disproved this and discovered that ironically, it's closely related to a group of small eagles in the genus Hiroetus.

Again, ironically, it's a sister species to a bird named of all things, the little eagle, which is found in Australia.

These closely related species weigh only about 1kg and have a wingspan of just over a meter.

Compared to the much greater weight, an estimated 2.5 to 3 meter wingspan of Haast's eagle.

The current evidence tells us that the most likely evolutionary scenario is a small-sized common ancestor made its way from Australia to New Zealand and began diverging from the original population around 2.2 million years ago.

Shockingly, however, there is only a genetic difference of 1.25% between Haast's eagle and the little eagle, despite their vastly opposing sizes.

So what ecological factors made or dare I say allowed Haast's eagle to become the behemoth that it was?

Well, it seems to have come down to the size of the prey available.

More, a group of large herbivores were an untapped food source.

There were no mammalian predators like large cats or canines around to hunt them.

Natural selection therefore allowed Haast's eagle to fill this niche as the sole megafauna predator.

It had to become big to be increasingly successful in this role.

By the way, how cool does that sound?

Saw a megafauna predator.

But what pushed larger individuals to begin to hunt more in the first place?

Starting the cascade of natural selection that would favour a bigger and bigger bird?

Well, a likely answer is competition for smaller prey.

You see, there were other similar vectors in New Zealand at the same time.

In particular, Isles Harrier, which funnily enough is also the largest harrier species known to have existed, but didn't get anywhere near as big as our eagle.

As we see in many other examples across the bird world, in terms of survival, it's often better to specialise in a food source rather than having to share it with other species.

Undoubtedly, Haast's eagle would have eaten some more medium-sized birds, as long as they weren't too small to grasp in its talons.

For instance, Kia, Paradise Sheldak, Takahe and Karkapur, alongside the extinct Edspill and New Zealand specific Koot and Goose species have all been suggested.

But by being able to focus on larger prey as well, it created a point of difference from other birds that ensured its survival.

Well, that was until humans came along and began hunting more themselves, not only taking this eagle's food source, but also likely changing crucial habitat as their settlement spread across the land.

This was a species that Haast's eagle couldn't out-of-volve, ultimately leading to its extinction.

We've said that Haast's eagle was able to hunt more, but how do we know this exactly?

Well, fossil evidence shows its telemarks on the bones of these fallen birds.

Despite its size, Al predator was still able to fly.

It had retained fully-developed shoulders and wings, unlike many other island giants, ironically, including them all.

And it seems it would begin either from a high perch like a trio cliff or a spring-up from a lower point using its powerful lead muscles to then attack from above.

It would grip onto the pelvic region first, knocking the moor off balance with a high-speed strike, and then deliver a killing blow to the head or neck with either its beak or talons.

Moor species came in many sizes, and this hunting tactic appears to have worked on even the largest 200 kg versions.

It might not be surprising, then, to find out that Haast's eagle could crush bones through even 5 cm of flesh.

I guess the saying's true. More eagles? More problems.

What it ate seems to be well-known, but where it hunted has been an area of a little more debate.

You see, Haast's eagle had proportionally short wings.

Now don't get me wrong, its wings stem was large in the absolute sense.

But relative to its body, it was on the shorter side.

This has led some researchers to believe it was an eagle that hunted within the forested areas of New Zealand, the shorter wings being an adaptation for maneuverability in this physically crowded environment.

More recently, however, it's been proposed to have inhabited and hunted in open areas like mountains and plains.

How could such a 180 in the scientific view have occurred?

Well, it mostly revolves around the likely ancestor of this bird, and when it made its way to New Zealand.

As mentioned earlier, around 2.2 million years ago was when Haast's eagle started to diverge, which aligns with the Pleistocene, a period marked by glaciers.

These frigid temperatures altered the environment, killing off forest and leaving more open terrain.

It's thought that this is what allowed the Australian ancestor, which if the Haast's eagle's closest relatives are anything to go by, was an inhabitant of open grass and woodlands to successfully establish in New Zealand.

Some additional points to mention here are that most fossils of this eagle had been found in open terrain, and other research has inferred that the neural circuitry needed for fine motor control of flight through a forest was not present in this bird.

Both of these, of course, support the open habitat scenario.

I hope you find all of this as interesting as I do, but it gets even better.

It's pretty clear Haast's eagle hunted like, well, an eagle, but did it feed like one?

Recent 3D shape analysis sheds light on this, and it turns out that while the beak and talons are distinctly eagle-like,

the cranium aka head is more consistent with a vulture.

Wait, what? Where did that come from, right?

Part of this is the presence of nostril scrolls, which are protrusions inside the nose that reduce the entry of foreign matter into this area when feeding inside a carcass.

The structure of the skull was also well adapted for pulling back motions of the head and neck, consistent with other vultures, and I presume is for a specific method of tearing flesh.

Additionally, from what I could gather from the paper, the skull of Haast's eagle looked more elongated than most of the other eagles used for comparison.

But take this with a grain of salt, as the diagrams were not to scale, and there were only a handful of species that were compared, so I could be wrong about this.

The reason I pointed out however, is that it logically, at least in my mind, would make it easier to probe inside a carcass to eat the internal organs.

The whole eagle beak vulture head scenario does raise a question though.

Without a vulture adapted beak, would we expect this bird to have been able to get through the tougher outer layers of its prey to access the softer insights?

The answer is yes, and the reasoning here is that while many vultures scavenge on tough-skinned mammals, Haast's eagle didn't have this option.

Birds were largely all that there were, and birds tend to have softer skin.

The last vulture-related point I want to raise today is the possibility that Haast's eagle head, wait for it, or featherless, or largely featherless head.

This is a common adaptation among vultures as a way to keep the head clean with their method of feeding, and why has this possibility been raised?

Well, in addition to other vulture-like traits being present on our featured bird, there is a specific ancient Maori rock drawing thought to depict this eagle.

In this picture, the body is colored in dark, while the head and neck are left uncolored.

Could this have been to show the difference in feathered dormant between these two parts?

A description passed down through generations of Maori tell us of it having a bunch of red feathers on the top of its head.

Okay, so now some evidence that it was at least partially feathered in this region.

Maybe the ancestors who made the rock drawing didn't have a red incalternative to signify this, who knows?

The rest of the description states that its feathers were otherwise black with hints of yellow and green, but here's where it gets interesting.

The same passage describes the bird's main colours as being black, red, and white.

Black makes hints for the body, red makes hints for the feathers on top of the head, but where does the white come from?

Could it be bare skin on the neck and remaining head area?

Again, we may never know, but it's dang interesting to think about.

Finally, this passage also describes that its resting place was on the top of mountains, which supports the idea from earlier that it lived in a more open habitat.

And that's a wrap for episode 37 of the Bloob's podcast.

Man, that went harsh, I mean fast.

Really, quite coincidentally, after starting research for this episode, I went on a short trip to the South Island.

A near where I was staying was a site featuring ancient Māori rock art.

I didn't get to see the one I talked about just before, but I did see others of Haas Eagle. It was so, so interesting.

I'll post in at some point on my Instagram page at mat.rocella.com.

That's m-a-t-t dot a-o-s-s-e-l-l-a.

If you've enjoyed the episode today and find the podcast interesting, then consider becoming a patron of the show.

You'll really be helping me out to upscale this work. You'll find the support the show link in the show notes.

Or you can go directly to patreon.com, full slash bloob's, 439.

Right now, this project might just be a little legal, but who knows, one day it could reach Haas Eagle status.

As always, thank you so much for listening. Remember, our current birds are awesome, ancient birds are awesome, and you are awesome.

I'll catch you next time.

D-D-D-D, bloops.