Meet the Baltic Dunlin
The dunlin is a shorebird that is widespread across the Northern Hemisphere. You can see them from Alaska in the far west to Kamtachka in the far east. Across this range, there are several subspecies, and the Baltic Dunlin belongs to the schinzii subspecies* that breed in Greenland, Scotland, NorthSea, and on coastal meadows around the Baltic Sea. The Baltic dunlin is maybe the most endangered shorebird population in Europe. The Finnish population has decreased from around 200 pairs at its peak in the 60s to less than 50 pairs nowadays, of which the majority breeds in the Bothnian Bay. As a result, the Baltic population is listed as an Annex I species in the European Birds Directive, highlighting the critical need for appropriate conservation measures. This year was particularly bad, with only 20 recorded breeding pairs in the Oulu region. To halt the steep decline, researchers experimented this year for the first time with headstarting as a method to boost the population. More on that later!
So, how can one recognize the schinzii subspecies? Compared to the alpina subspecies -which is rather common in the (sub) Arctic- schinzii birds are a bit smaller, have a shorter bill, and most importantly, they have a duller colored summer plumage and often lack the full black belly. Differentiating both subspecies in their winter plumage is nearly impossible. The Baltic dunlin visits the Bothnian coastal meadows from May to July before returning to its wintering grounds in North Africa, with Banc D'Arguin in Mauritania as a prime destination. During their migration, they spend quite some time in the Wadden Sea. They eat here their fill before embarking on the long journey to Africa. Let us now delve into the research being carried out in Oulu to find out why the life of the southern dunlin is so dangerous.
* Subspecies: A subspecies is a group of individuals within a species that are highly genetically and often morphologically differentiated. However, subspecies can still interbreed. Two species that successfully interbreed almost always produce offspring with highly reduced survival.
This photo shows a dunlin ssp alpina. Note the ruddy back and black belly. In the schintzii subspecies, the ruddy tones are less bright, and the black belly not uniform.
On the highway towards extinction?
Kari Koivula and Veli-Matti Pakannen have been conducting research on the dunlin in the Bay of Bothnia for more than two decades. Over the years, they had a front-row seat to experience the decline of the dunlin population.
Each year in early May, when the first male dunlins arrive, researchers from the Oulu biology department start to gather population data. Upon arriving at the breeding grounds, the male dunlin immediately starts searching for a suitable territory in short grass patches. Male dunlins often use the same territory for several years. In addition, males are monogamous. Therefore, they will wait first for the female that mated with them the previous year. Cute, isn’t it?
Displaying males are relatively easy to find due to their distinctive sound and butterfly-like display flights. Once the male successfully attracts a female, he prepares several nest cups in the grass for her to select from.
Now, the challenging part starts: finding nests! The eggs are tiny and well camouflaged due to their earth green coloration. Even when you know the GPS coordinates of the nest location, you have to use additional landmarks to find it since the nest cup can remain invisible in the tangle of grass.
Searching nests is pretty straightforward. You just walk and walk until you flush a bird from the nest. Then you try to spot the eggs, which can be very tricky.
After the eggs have hatched, dunlin chicks and their parent(s) get a metal ring. Adult birds get an additional color ring code to easily recognize them in the field. Researchers also take blood samples from the birds. This is crucial for genetic analyses, such as quantifying inbreeding, and determining the sex of the individual, especially young chicks. To collect all this data, researchers must walk kilometers and kilometers through the coastal meadows, often without any success, but sometimes one gets lucky! One evening, while searching for ruff nests, colleagues noticed an adult color banded male dunlin alarming. The next day, Vellu went to investigate—and sure enough, the bird had a nest with four eggs, nearly ready to hatch! A few days later, we had the privilege of a special visit: under the pink sky, we banded the chicks. Maybe there’s still a glimmer of hope?
Jelena opens a bag of hand warmers to keep the chicks warm while ringing.
A 1-day-old chick receives it metal ring;
1-day-old dunlin chicks, they are cute, aren't they?
There are several reasons why the Baltic dunlin population is declining. To understand the reason for their dramatic declines, it is important to understand their breeding habitat. Coastal meadows as we know today are not untouched natural landscapes. They are largely human-made. Before, they survived in small numbers in short-growed habitats that developed on emerging land due to land-uplifting*.
Coastal meadows are recognized for their biological and cultural significance as “traditional rural biotopes”. To control the overgrowth of grass and reeds, cattle were used to graze these meadows. This traditional management has been abandoned after the 1960ies, and many of these meadows have become overgrown with vegetation. But, over the past years, coastal grassland restoration by cattle grazing has started again.One would think that this is a solution to the problem of overgrowth. In reality, these management measures can be very risky and are site-dependent. If the cattle are in the breeding area in inadequate timing and number, dunlins might find themselves in a trap, and the inland meadow will still be overgrown with little to no place to nest. One solution might be mowing grasslands at the end of the summer. Moreover, enhanced nitrogen deposition and more nutrient-rich water from the Bothnian Bay make the meadows more productive. As a consequence, grass and reeds grow much faster, complicating the habitat management of these meadows.
Coastal meadows often get flooded later in the summer because of strong southwest winds that blow water from the Baltic sea into the Botnian bay. Because of climate change, these floods occur more often earlier in the season when the birds have either nests or chicks. This kind of flooding can have devastating consequences for the population. Habitat and flooding problems are closely connected. Since more inland areas of the meadows tend to get overgrown by higher grass or reeds, dunlins are forced to breed close to the shoreline where the grass is shorter but where the risk for flooding is the highest. They find themselves caught between a solution (shorter grass close to the shoreline) and a new problem (flooding risk).
*A large pack of ice pressed on the Fennoscandian land during the last ice-age. Since the ice and associated pressure on the land has disappeared, land is lifting upwards. Because of this, countless small islands emerge in front of the Swedish and Finnish coast.
Summer flooding in the meadow
To make it even more disheartening, there is something called “inbreeding”. Small populations, with limited movement – such as the Baltic dunlin – are particularly vulnerable. Inbreeding means that closely related individuals breed with each other. This has negative consequences on the survival of the offspring, putting the population even at a higher extinction risk. Ecologists use a dramatic term for this process, where negative effects amplify each other: the extinction vortex!
I will end with the most “natural” problem: predation. Living in coastal meadows doesn’t come without any risks. A wide range of predators profit from the abundant food source available here. Goshawks, harriers, kestrels, peregrine falcons,…, and foxes visit the meadows in search of food for themselves, and their young. In years when there are a lot of voles available in the forests and inland field areas, the hunting pressure on birds in coastal meadows is lower. Unfortunately, the vole cycle is not as predictable as it used to be and probably motivates predators to shift to a more avian diet.
There are not many options left to save a small, endangered population such as the Baltic dunlin. One of these last resorts that the wader group of Oulu starts trying is head-starting.
A cute video to cheer up this potentially depressing blog. Here you can see the adult male starting to brood on the chicks again after ringing. The males are mainly responsible for raising the chicks.
Headstarting as a last resort?
Headstarting is a conservation practice that has increased in popularity in recent years. The first step in a head-starting project is to collect the eggs from breeding pairs in the field. In many projects, the researchers remove the eggs from the nest cup and leave the nest cup empty. If this is done early enough in the nesting stage, there is a high chance that the parents will make a new nest. But, this also means more work for the researchers - they have to take up a parental role and raise wader chicks until they are ready to fledge. This mostly means providing sufficient food and water since wader chicks are precocial, meaning they can walk and feed themselves straight after hatching. Researchers can avoid the parent freak out when they find an empty nest cup by replacing the real eggs with the dummy eggs. However, birds may still see through this trick and abandon the original nest. They can still start a new nest elsewhere, which can be beneficial, as it means that the next generation of dunlins will be larger. Once researchers have collected the eggs from the field, the eggs are transported to the incubators at the university facilities.
Eggs of three dunlin clutches in the incubator of the Oulu University. It takes about 22 days for dunlin eggs to hatch.
In Oulu, we preferred to return the chicks to their parents as soon as possible if they were still brooding the artificial eggs.. We were not yet prepared to care for a bunch of chicks as it was the project’s first year. Unfortunately, some chicks lost their parents, or their parents abandoned the original nest. Eventually, we had to play "parent dunlin" for four chicks.
For the first week, the chicks stayed at the university facilities in Oulu. It was a very intense week. Young chicks are helpless beings, not used to a captive world without an adult bird to show them the way. One chick died during the first days, and one bird (known as Yellow) nearly drowned in its drinking water. Being a parent is a stressful job—especially when your kids are waders.
It should come as no surprise that we were thrilled when the chicks came to our fieldhouse garden. WithVellu, Lisa, and Jenni, we made a cage in the garden for the three chicks in need of parental care. The chicks would remain in the garden for about two more weeks to adjust to outdoor living and continue growing. Our parental duties included weighing the chicks and feeding them several times a day. It was truly amazing to see them grow every single day. Birds could gain multiple grams a day! In addition to their food from the pet store, I went out with my butterfly net catching mosquitoes. For once, I was happy about the abundance of mosquitoes in the North! After a night in the freezer, these mosquitoes were a delicious meal for the fast-growing chicks.
Initially, chick "Yellow" was rather shy in the new cage.
But soon it started to wander around!
They grow so fast! During some days they could earn up to three grams body mass!
I also started to spy on the chicks using a Go-Pro camera. With most of the other field tasks nearly done, I had time to experiment with this magical cube. I could film the first time they tried to fly, the first time a bird tried to catch a fly, or when they bathed. By closely observing the chicks, we noticed that each bird had its personality, just like humans. Yellow was the biggest daredevil and not shy at all to pose in front of the camera. Red and Green preferred to spend most of their time sheltered under the box. Yellow was also the bird that grew the most. Yellow is likely female, as females are generally larger than males. After about ten days, the daily feeding routine became more challenging as the birds began flying around the cage, the sign it was time to release the youngsters into the wild.
GoPro video showing the first attempt of Yellow to catch an insect!
We released the chicks near a tern and little gull colony in a nearby nature reserve. Terns and little gulls are pretty aggressive towards intruders such as humans and predators, providing a safe space for the chicks. Indeed, ruff and redshank broods often forage near the bird colony to profit from free safety alarms.
Although I was happy with the little dunlins roaming freely, I got tears in my eyes. I hope they will survive their dangerous adventures yet to come. They hopefully almost arrived at their wintering ground in Africa, where they will spend nearly two years, although females often return after one year. May next year, I hope to receive a text saying one of "my kids" is back!
And there they go, hopefully ready for the big wild world full of danger.
Hopefully, this headstarting project will get the Baltic Dunlin population away from the highway to extinction. Anyway, these dunlins have won a special place in my heart, and maybe in yours too?
The relief was great when we saw the young birds foraging as if they had never done anything else.
Written with much appreciated thanks to the feedback from Jelena Belojevic!
More information:
- About Baltic dunlin migration: A paper by Veli-Matti Pakanen and others titled "Migration strategies of the Baltic dunlin: rapid jump migration in the autumn but slower skipping type spring migration"
- About the flooding problem: A pre-print paper by Kari Koivula and others titled "Increased Wind Flood Frequency Leads to Decreased Nest Success of Endangered Waders in Managed Shore Meadows"
- About the inbreeding problem and extinction vortex: A paper by Donald Blomqvist and others titled "Trapped in the extinction vortex? Strong genetic effects in a declining vertebrate population" on the Swedish Baltic dunlin population
- About the habitat changes in the Botnian bay and a broader genetic context: A paper by Nelli Rönkä and others titled "Genetic differentiation in an endangered and strongly philopatric, migrant shorebird"
- About the disturbed vole cycle and its influence: A paper by Veli-Matti Pakanen and others titled "The abundance of small mammals is positively linked to survival from nest depredation but negatively linked to local recruitment of a ground nesting precocial bird"
- About the Swedish Baltic dunlin conservation project: https://en.nordensark.se/nyhetsarkiv/head-start-for-southern-dunlins/
- About a British headstart project focussing on godwits: https://www.waderquest.net/conservation/headstarting/