Death by Parasitism in Darwin’s Finches

Death by Parasitism in Darwin’s Finches

Galapagos isn’t just about tame, cute, intriguing animals and exotic landscapes. The islands are home to many invasive species and diseases that threaten its wildlife, and you should be warned, this post may gross you out. Since 2004 on Floreana Island, Sonia Kleindorfer, Rachael Dudaniec and others have been studying one of the major problems threatening Galapagos land birds, the introduced parasitic fly, Philornis downsi (pictured above), which feeds on the blood of growing nestlings in Darwin´s finch nests. The fly is thought to have been introduced to the islands via fruit or live chicken imports from the Ecuadorian mainland, and was first discovered in finch nests in 1997. However, some Philornis flies were found in museum collections made in 1964, though it wasn’t noticed as a problem until about 30 years later. We are working together with Charlotte Causton from the Charles Darwin Research Station, who is coordinating the international program to address Philornis on the Galapagos Islands.

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A nicely positioned nest right by the sea in an Opuntia cactus:-)

The adult flies lay their eggs in finch nests; egg laying by adult flies has rarely been observed. Our in-nest videos showed adult flies walking over finch eggs and laying fly eggs in nests with newly hatched finch chicks (see this). The fly larvae feed on the blood and tissues of nestlings, and frequently kill all nestlings in a nest before the chicks can fledge. The larvae reside in the nesting material, and feed on nestling blood for about 5 days before pupating at the base of the nest. The flies then emerge into the non-parasitic adult fly stage about 10 days later. These flies are very robust and are known to live up to 280 days in the laboratory (pers. comm. Charlotte Causton), so that’s a lot of nests that can be infested by a single female fly. Our group has found that in-nest mortality of chicks ranges between 20-100% across years (see here). We also showed that finch species differ in how many parasites they have in their nests, and in their ability to survive (see here). The parasitic larvae are surprisingly large and can reach up to 1.8 cm in length – so the death rate is perhaps not surprising when you imagine 30 of these feeding on a single little nestling.


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The adult, non parasitic life stage of Philornis downsi
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This nest is ready to be pulled apart so we can count its parasites and preserve them in ethanol for later analysis….
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These are fly pupae, which cluster together in the nesting material, forming little cocoons at the base of the nest.

The parasite is a huge problem for declining local finch populations and localised species like the endangered Mangrove Finch on Isabela Island (less than 200 pairs) and Medium Tree Finch on Floreana Island (around 5000 birds left in the world). This year, working on Floreana and Santa Cruz, we have found many inactive nests containing dead chicks that have died from Philornis parasitism. The chicks seem to die off one by one, with the healthiest chicks avoiding larvae by standing over their siblings. The sibling at the bottom of the pile dies first but also acts as a buffer for its siblings standing on top of it.  When all the other siblings  have died one by one, the single remaining chick is left to endure the full onslaught of hungry fly larvae, succumbing to death sometimes within a few hours. The Medium Ground Finch nestling pictured below is an example of this. This solitary nestling appeared fine when discovered at 8am one morning, but when we returned at 10.30am the nestling was dead with many holes from larvae found all over its body. This is one vicious fly.



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This unfortunate nestling was found dead in the nest within 2.5 hrs of being attacked by parasites

A large part of our work here is monitoring nests and collecting them once they become inactive due to death by parasitism, predation or abandonment. We tear the nests apart carefully to count every single Philornis larva and pupa within the nest. This year we are finding about 30-40 per nest on average, but recently found one with 114!! For each nest we count the number of 1st, 2nd and 3rd larval instars as well as pupa and empty pupa cases (emerged flies). They are rather disgusting things, to say it mildly (see below).



2nd and 3rd instar Philornis  parasitic larvae. The dark patches on their bodies is bird blood  they have fed on- ewww…


Philornis fly pupae

Previous genetic analysis done by our group on the flies across islands found there is pretty high connectivity of fly populations across islands, and across the highland and lowland habitats (published here ). Genetics has also provided insight in to how many flies lay their eggs in a single nest (published here).

The effects of the larvae can be seen here: Enlarged bird nostrils (called ‘nari’) caused by the larvae burrowing their way in to the body. The large nari are frequently seen through to adulthood and may affect bird song and the ability to attract mates


From our and others observations, it seems that things are beginning to changing over the last 12-15 years, with some evidence that these incredibly harmful parasites may be showing signs of co-evolution with their hosts (e.g. see here). Co-evolution in hosts and parasites may lead to less mortality among nestlings, which ultimately will act to ensure that fly populations are sustained with a sure supply of hosts in the long run. For example, our group (Kleindorfer et al.) has documented increasing hybridisation among Floreana tree finch species, and hybrid birds have lower numbers of parasites and fledge more nestlings (see here). If hybridisation is good for combating Philornis, this suggests the fly is directing Darwin finch populations along new evolutionary trajectories.

This poor little guy has an infected would on his belly from the blood sucking larvae

We can’t just wait for evolution to ‘do its thing’ though – death rates are way too high for that. This is why many researchers are currently working very hard at the Charles Darwin Research Station and in the United States to develop control methods for the fly. These range from chemical eradication by spraying nests with insecticide, to developing pheromonal compounds to attract adult flies to traps.


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Removing Day 1-2 small ground finch chicks and egg from a nest before spraying it with insecticide to kill the parasites

There is also work on the potential of using ‘parasitoids’ to control fly numbers, which are insect parasites of the parasitic fly itself. A lot of work is also being done to try and find weaknesses in the fly’s reproductive cycle that could indicate prime times for control measures. Breeding the flies is proving difficult though, and this important work continues by research groups around the globe.

Spraying the base of a nest with insecticide to eliminate parasites
10 day old chicks cozy in their newly sprayed nest

Clearly one thing missing from the puzzle is funding, and unfortunately, money for research and implementing control measures may be the one thing that holds us from solving this issue – the biggest threat to the worlds’ fastest evolving group of birds. With all of this knowledge combined with careful conservation decisions and action, Darwin’s finches will continue to provide insight into how different life forms come into being.


Opuntia cacti in Garrapatero, Santa Cruz, where the finches prefer to nest

Floreana Island

Floreana Island

Floreana has the smallest number of people living on it out of all the Galapagos Islands (just 160) making it a unique experience for us to interact with the friendly community (including marine iguanas, featured above) and integrate in to daily life there. Sonia initiated her work on this island in 2004, so luckily we already know well who to ask for various items like bread, eggs, and a lift up to our field sites each day. Floreana is no tropical paradise, despite the visions brought by the island’s first European settlers in the 1930’s. It is a hot and harsh environment with many thorny trees, sharp unstable lava rocks and no paved roads. In all its rawness it still exerts an enchanting and unique beauty, where the animals seems to approach humans with the same curiosity as we approach them.

We just arrived back in Santa Cruz yesterday after about 2 weeks of mist-netting and searching for finch nests near Cerro Pajas volcano (below) and in the lowlands. The island has been super hot and dry despite fears of torrential El Nino rains, and the number of active Darwin’s finch nests was really low. Because of this, we came back to Santa Cruz earlier where the rains have been a little more frequent and nests are more active. It was so unusually hot this year on Floreana that most of our team seemed to ‘pass out’ at least an hour a day in the afternoons, and we sometimes took to sleeping outside in hope of a fresh ocean breeze. However, we caught many dozens of Darwin’s finches in the lowlands and highlands (pictured), leaving content with our time there….

Cerro Pajas (inactive volcano) has the highest elevation on the island and is covered in a Scalesia-mixed forest – our study site winds around the right side of the crater and into the center of it.  Photo: R Dudaniec
Taken from the base of Cerro Pajas. Photo: R Dudaniec
Setting up a mist-net early one morning at the base of misty Cerro Pajas. Photo: W Loo

Although back here in the ‘big town’ of Puerto Ayora we aren’t witnessing a constant wildlife documentary on our doorstep overlooking the sea, the high speed internet, less biting insects, and access to air-conditioning is a total luxury….

Here are a few more photos that hopefully capture the atmosphere of this special island, as well as what we have been up to….

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Sunrise in the lowlands looking up to Cerro Pajas. Photo R Dudaniec
A small ground finch nest in the lowlands – we spend a lot of time searching for these! Note the use of ‘Darwin’s cotton’ to make the nest – a native cotton that grows in the lowlands. Photo: R Dudaniec
The lowlands of Floreana – in constrast to the highlands, are very dry and almost leafless due to the lack of rain. This area is full of thorny bushes and cacti that keep finch nests a bit safer from predators, like rats.  The white trees are the beautifully-scented ‘Palo Santo’. Photo R Dudaniec
Left to Right: Jefferson, Rachael, Sonia and Wesley, next a rock carving done by an early European settler as a joke to trick anthropologists. There were no native people of Galapagos….
A Galapagos tortoise in the Floreana tortoise sanctuary. Photo: J Garcia Loortortoise

There is a legend on Galapagos called ‘The curse of the giant tortoise’ – which states that when the tortoise looks into your eyes, it can assess whether you bring good or bad intentions to the islands, and if bad, it will curse you with some horrible fate….

Galapagos fur seals at the ‘La Loberia’, which is a favourite breeding site on Floreana (though not too many this year due to El Nino). This is a mother and her pup. Photo: W Loo
An amazing shot of a Blue-footed Booby by W Loo



Our home and field station for the last two weeks is pictured here on La Playa Negra (Black Beach, where Charles Darwin came ashore) – the house furthest to the right, where sea turtles and marine iguanas nest on the beach in front, and pelicans, Galapagos penguins and sea lions drift pass on the waves. There is also a HUGE diversity of insects, including scorpians, wasps, spiders and grasshoppers….;-) eek.

A hermit crab from La Playa Negra. Photo: R Dudaniec with help from ‘hermit crab whisperer’ J Garcia Loor






Life in Puerto Ayora, Galapagos

Life in Puerto Ayora, Galapagos

Many people ask ‘are there people living on the Galapagos Islands?”. The answer is definitely YES, 25 000 of them. There are four main inhabited islands. Most people are in the town of Puerto Ayora, Santa Cruz, the first stop for most tourists flying into Galapagos. It is a bustling touristy town full of restaurants, banks, bars and boats, with pelicans, sea lions and marine iguanas recuperating from their maritime meals. This is where tourists book their tours and dives, and buy every sort of souvenir available with a tortoise, sea lion or blue-footed booby on it. Though an inspiring gateway to the Galapagos, one aspect of living in Puerto Ayora is the lack of clean drinking water, so keeping track of how much drinking water you have left each day and making sure you keep your mouth shut while showering keeps one ‘present’.

We are now on Floreana Island, where the internet is is like an elusive ghost that sometimes appears (so a short post) but we’ll do our best to share what we have been up to soon. First here are a few glimpses of what we left behind in Puerto Ayora…

The Santa Cruz fishing dock is a hub of activity each day. Fish are distributed throughout the towns’ restaurants and people, coming straight off the boats seen in the background.


Entrance to the Charles Darwin Research Station
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Example of an Ecuadorian ‘almuerzo’ (set lunch) – delish!
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The ‘Kioskos’- lots of baked fish, beans and rice

Meanwhile, we arrived on Floreana a few days ago, and are heading up to the highlands of Floreana each day at 5.30am to catch birds and find nests, which involves hiking through the thorny ‘cats claw’ trees, entangling vines, and dealing with mosquitos and the fire ants, which bite your neck and ankles. It’s all worth it though in the afternoon when you get to watch sea turtles swimming by from the porch;-) Life is much simpler here; there is one house that sells bread, another that sells eggs, but you can’t really buy anything else. There are no paved roads and the population is 160. More from Floreana soon!

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all the gear we took to Floreana, ready for loading on to the boat
….and an old friend was there to meet us on arrival at Floreana. Photo: Sonia Kleindorfer





Meeting the finches: week 1

Meeting the finches: week 1

Week 1 on Santa Cruz Island

After more than 35 hours of travel and 4 flights later from Australia, half of our team (Sonia Kleindorfer and Rachael Dudaniec) arrived at Baltra airport, with all gear in hand:-). The other half of our team also made it successfully: PhD student Wesley Loo, from Harvard University, MA, and field assistant, Jefferson Garcia Loor from the Central University of Ecuador in Quito. So far we have had 4 full days out in the field under the Equatorial sun – some of us re-acquainting with old finch friends, some of us making new ones….


Our mission on Santa Cruz

Our broad aim for our ~10 days on Santa Cruz is to capture and sample 10 birds per Darwin finch species in each of the lowland and highland habitats – that’s nine different species! Each bird we catch is carefully measured, weighed, sampled for DNA analysis, and then released.

Darwin’s finches

Not all species of Darwin’s finches live on every island – there are 13 species in total and each species has a unique set of morphological and behavioural features that makes them ecologically different. There are two main groups: the ground finches (found mainly in the lowlands) and the tree finches (found mainly the highlands).

Here’s how we went in week 1, including some pictures of the endemic and strikingly tame creatures that roam these often harsh, rocky volcanic islands. It has been nothing less than a flurry of feathers and activity…..

DAY 1 Garrapatero Beach, Santa Cruz, Lowlands Habitat

The Galapagos finches occupy two main natural habitats – the hot, rocky and thorny lowlands and the humid, rainy and shadier highlands . We decided to get our field work started in the lowlands, at Garrapatero beach area, where Darwin’s ground finches are super abundant.

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This is a mist-net that we use to capture the birds. We play recordings of different songs of the finches, which attracts them to the area, and if we are lucky, they will fly into the net! (Note flamingos in background;-)
Just 50 meters from our mist-nests were pink flamingos, gracefully feeding in the lagoon. photo: J Garcia

Today we caught a bunch of small ground finches, medium ground finches and a cactus finch (pictured), named because it feeds on the flowers of the Opuntia cacti that are spread throughout the lowlands (pictured in last post).

The Cactus finch – Geospiza scandens.                                                    photo: R Dudaniec

DAYS 2 and 3:  Los Gemelos (‘The Twins’), Santa Cruz, Highland Habitat

It was a relief to go from the extremely hot and harsh lowlands to the lush, green and shady highlands! Our study site is in the Scalesia forest of the highlands, at Los Gemelos, named because of two giant volcanic sink holes located there.

Scalesia trees in the highlands, Los Gemelos.     photo: S Kleindorfer
Our bird banding station in the Scalesia forest. Note coffee thermos. Work starts at sunrise.

The Scalesia trees are home to the tree finches, some of which we caught and are pictured below…

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The Large Tree Finch (Camarhynchus psittacula) – named for having the largest beak of all the tree finches.. This is a male, shown by its black neck plumage. Photo: R Dudaniec
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The Woodpecker Finch (Camarhynchus pallidus) – often seen using tools and its long beak to pry out insects from the bark. Photo: R Dudaniec
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Sonia – happy with a Small tree finch 🙂
Some of us were lucky to see this beautiful barn owl. photo: J Garcia

DAY 4 – Garrapatero Lowlands

Back to the lowlands in Garrapatero! So much activity this morning….and we were very busy at the mist-net. The most exciting species we got today was the very large-beaked Large ground finch (Geospiza magnirostris). These guys need their large beaks for crunching on hard seeds, and they definitely know how to defend themselves!

Large Ground Finch (Geospiza magnirostris).    photo: W Loo
Measuring the beak….          photo: W Loo
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…and at the end of the day, we stop to ponder and take a little cafecito.. (left to right – Jefferson, Wesley, Rachael)


In a couple of days we travel the island of Floreana, where we will start to find finch nests and monitor the impacts of the devasting introduced parasitic fly, Philornis downsi, and catch more birds for about 3 weeks…we can’t wait to get there and see what is going on! Stay tuned! 🙂

The red balloons show our field locations- Santa Cruz is the island in the middle, and Floreana at the bottom. Isabela, the largest island of the Galapagos, is the seahorse shaped island. Santa Cruz has a human population of approximately 20 000 people, and Floreana approximately 100.



A journey with the finches of Galapagos

A journey with the finches of Galapagos

On January 23rd, 2016, we embark on a 4-week journey to study the famous group of birds, Darwin’s finches, on the unique and treasured Galapagos Islands.

Our team? Two researchers from Australia: Professor Sonia Kleindorfer from Flinders University (Adelaide, SA), Dr Rachael Dudaniec from Macquarie University (Sydney, NSW), PhD student from Harvard University (USA), and a field ornithologist assistant from Ecuador. We are biologists (in Animal Behaviour, Conservation Genomics, Evolutionary Ecology) building upon a long-term study of Darwin’s finches on the Galapagos Islands.

What are we doing? We are setting out to answer questions about the impacts and evolution of a deadly introduced parasitic fly, Philornis downsi, that kills the majority of nestling finches on Galapagos. We are also out to answer questions about speciation and hybridisation among the finches, and how to best manage their declining populations.

To do this, we will spend 4 weeks with Darwin’s finches in the field, finding their nests, catching them, measuring them and monitoring their survival and populations. We will also be facing whatever this years’ El Niño decides to bring…like rain, rain, and more rain….

Follow this space! Here we will share what we are up to, our best photos, videos and the unexpected spectacles that occur during our field work 🙂



The Small Ground Finch (Geospiza fuliginosa)                          photo: Tim Clark
The Small Tree Finch (Camarhynchus parvulus)                               photo: Tim Clark
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Philornis downsi, the introduced fly with blood-sucking larvae that kill Darwin’s finch nestlings in the nest