New scientific research: translocation of Aquatic warblers might be more successful than was thought

One of the two translocated females of Aquatic warbler, that was managed to find during field studies at the Žuvintas Biosphere Reserve. Special plastic ring no. 7E.

DNA tests of Aquatic warblers, translocated from Belarus to Lithuania last year show that the number of males and females is more or less the same (42% and 58% respectively). According to the researchers, these results show that the translocation of these rare birds, which success is already being evaluated well by the international biologists’ community, may be even more effective, than it was thought so far.

This summer, experts managed to find 11 returned birds, that were translocated to Žuvintas in 2018. These included 9 males and 2 females. While finding males for experts is not difficult – when the sun sets. they sing loudly at the tops of the grass, finding females causes much more difficulties. They are masters of disguise – they don’t sing, hide deep in the sedges and start to make sounds only when approached, or when the chicks are already out of nest – the females move to the adjacent reeds with the chicks, where it is even more difficult to find the birds.

“Despite the fact that the female searches were carried out by very experienced Belarusian and Lithuanian specialists for several days, and after that we went to the sites ourselves almost every day, we managed to find only 2 females. Back then, experts speculated that there were probably more females, but they were deeper in the high reeds, making it very difficult to find them. The results of DNA testing indicate that there should be no less females than males, so it may be that the experts were not mistaken and that the translocation of Aquatic warblers was even more effective than we found in the field studies. These science-based considerations only confirm that our successful experience as one of the first biologists to test the translocation method with Aquatic warblers can be crucial to preserving this unique species from extinction.” – Žymantas Morkvėnas, Director of the Baltic Environmental Forum who coordinated the translocation of Aquatic warbler, commented on the new DNA test results.

Belarusian ornithologists are searching for females of Aquatic warbler by “combing” the sedge fens in the Žuvintas Biosphere Reserve

DNA testing for birds gender determination – effective, but rare practice

The gender of Aquatic warblers was determined by analyzing the DNA extracted from their blood samples. “Bird sex determination by DNA testing is not a common practice, relying more often on differences in appearance or behavioural characteristics between individuals of different sexes. However, it is even impossible to determine birds’ gender by their appearance when they are young and just begun to fly, so therefore the DNA examination was the only suitable method for us” says Baltic Environmental Forum ornithologist Gintaras Riauba.

Senior Researcher, P. B. Šivickis Parasitology Laboratory, Nature Research Center, dr. Vaidas Palinauskas takes blood samples from Aquatic warblers, from which the DNA was extracted for birds’ sex determination

Senior researcher at the P. B. Šivickis Parasitology Laboratory, Nature Research Center, dr. Vaidas Palinauskas says: “The sex chromosomes of birds are slightly different than human chromosomes, but the sex determination procedure is quite common: pure DNA is extracted from a tiny droplet of bird’s blood, the solution of which is used to multiply a certain corresponding DNA fragment. Later, the amplified DNA is passed through a special gel, where, figuratively speaking, the race of DNA fragments is happening. Let’s imagine that both a male and a female have 2 runners (DNA fragments) each, running in the gel. The two male runners run the same distance, while one of the female runners is behind. In the gel picture we see the result of such race – the two male runners overlap and therefore form one narrower strip, while two female runners stop side by side and form a wider (double) strip. Interestingly, the difficulty in determining the sex of birds depends on the species of bird. Often, sex determination by DNA testing of birds found in nature is a well-established practice and the protocols (i.e., following the same imaginative comparison, would follow the competition rules) are clearly described. Although, what is suitable for one species of birds may not be entirely appropriate for another because of the genetic differences between the species. Aquatic warblers are one of the rarest in Europe, and there is very little of such research. We encountered difficulties while examining the sex of the translocated Aquatic warblers, as even widely used protocols were not suitable. Finally, during the consultations with colleagues from the University of Lund in Swede, the appropriate primers and so-called polymerase chain reaction protocols have been adapted”.

A “race” of DNA fragments in a special gel. Male’s the two “runners” (DNA fragments) “run” the same distance, overlapping and thus form one narrower band, while the female two “runners” stop adjacent and form a wider (double) band. Photo by Nature Research Center

The results of DNA testing in Lithuania largely coincides with the results of earlier studies and the literature on the sex ratio of Aquatic warblers – the number of males and females in broods is more or less the same (about 55% of males and 45 of females).

Juveniles health also examined – blood parasites not found

Aquatic warbler chick hiding deep in grass in Žuvintas Biosphere Reserve

DNA extracted from birds’ blood has been used as an opportunity to check the health of the birds and to test them for diseases caused by blood parasites, including malaria. “Birds of the warblers family can be infected with blood parasites not only in breeding areas but also when migrating to Africa or southern Europe, so birds can also carry a variety of infections when flying out of the tropics,” said dr. V. Palinauskas. Using special markers, in the P. B. Šivickis Parasitology Laboratory it was investigated whether juveniles were infected with haemosporidia. Results of parasite DNA testing revealed that all juveniles were healthy. The good health and physical condition of the birds, before release gives great hope that most of them will survive the migration period and will return to Lithuania in the spring.

You can find out more about taking of blood from Aquatic warblers and preparation of blood samples for both sex determination and diagnosis of blood parasites by watching the special video blog series.

Dr. Vaidas Palinauskas draws blood from translocated Aquatic warblers

The translocation of Aquatic warblers was carried out in 2018-2019. In total, 100 rare birds were brought to the Žuvintas Biosphere Reserve from the largest habitat of these birds in Belarus. In 2018 98% of the birds were successfully bred and released. During the search of birds it was revealed that at least 11 birds (22%) returned. Previously, researchers had agreed that a 20% return rate would be a complete success. It is worth to be happy that all 50 Aquatic warbler chicks that were brought to Žuvintas in 2019 were successfully raised and released. This is 100% survival rate.

The translocation of Aquatic warblers is only one of the activities of this species conservation project, which will last for 7 years in Lithuania and Belarus, and makes up about 5 % of the total budget. During the project 20,000 ha of Aquatic warbler habitats where a large number of other species find place – great snipes, common redshanks, corncrakes and other birds, will be restored by managing water levels and building a biomass processing facility in Dreverna to address the issue of late-cut grass removal from fields, nature education and communication activities.

More about Aquatic warbler conservation in Lithuania and Belarus.