"Researchers' time is limited - you can't get everywhere. The more participants and people are involved in your research, the more you can achieve," said Ülo Väli, a senior researcher at the Estonian University of Life Sciences (EMÜ). Although a team of scientists can accomplish more than a single researcher, yet another way to increase the scope of you research is to involve citizen scientists. "In this way more people are involved in field data collection, and the geographical scope or spatial coverage is often much larger as well. You could even collect information from all over the world, if you wanted," Väli said.

Together with Ana Magalhaes, an intern and an exchange student at EMÜ, Ülo Väli tested the suitability of citizen science data for ecology and conservation research. Specifically, they monitored the content related to the diet composition of the lesser spotted eagle posted online by volunteers monitoring the nests of four eagle pairs breeding in Estonia.

Review of observations

Citizen science often means that people around the world collect small samples of field data, which later forms a large and representative block that enables a more detailed analysis, said Ülo Väli, and added: "Our case was a little different, we had people all over the world sitting at home behind their computers and following webcams directed at only four designated bird nests", said Väli.

Although all nests were located in east-central Estonia (Jõgeva and Tartu counties), i.e., the geographical coverage of the survey was small, people in different parts of the world could follow what was happening in them. "Due to the fact that the birdwatchers were all over the world, the events related to the research have been recorded continuously. For instance, when the Estonians slept, the Americans were still up somewhere," Väli said.

Väli said, hundreds of wildlife internet cameras (webcams) have been installed in Estonia and increasingly grow in popularity with many open forums emerging around them. "People spontaneously are jotting down everything they see while watching webcams and share their impressions and knowledge online," said Väli. So the researchers themselves did not give the eagle enthusiasts any tasks, but only reviewed their forum posts.

"Not much happens in the nests," said Väli, and noted: "A big event could be, for example, when birds deliver prey or simply fly in and out. It is also exciting to see when the chicks start hatching and the young learn to fly. A separate topic is the division of labor between male and female birds. "What and when was brought to the nest has been spotted and recorded. We have used this data for our research as well," said the senior researcher.

A frog or a mouse?

Ülo Väli admitted, he chose the lesser spotted eagle for this study, partly for his subjective feeling of admiration for the species. However, together with Asko Lõhmus from the University of Tartu and within his own research group at EMÜ, Väli had already extensively studied the lesser spotted eagle before, which is the model species in ecological studies and a flagship species in conservation research.

From the conservation point of view, this species of eagle is very well suited to be examined, because these birds depend on the agricultural landscape for their livelihood. "The prey they catch - voles, frogs, moles, and smaller open-field birds - reflect the state of the agricultural landscape," said the senior researcher.

The diet of the lesser spotted eagle is mainly composed of meadow voles and, to a lesser extent of other smaller mammals, such as northern water voles and little weasels, said Väli, and noted that, "another important item in their spring diet is frogs." Even though frogs completely disappear from the diet composition by the summer start, the spring webcam recordings provide ample evidence to the fact that frogs make up an important part of the diet at this time of the year.

The traditional method of determining the diet of raptors is based on the analyses of pellets and prey remains collected at nests. This method provides data for only a short period prior to the collection of the material, and so considerably underestimates the proportion of frogs in the diet of eagles. The direct observations from webcams, however, show that "the lesser spotted eagle mainly feeds on frogs until the beginning of May," said Väli.

Väli added that the proportion of voles and other smaller mammals gradually increases and plays an important role in the diet only from May onwards with smaller birds being added to the diet in mid-summer, when they are most abundant after their offspring fledging. Indeed, passerines' fledglings are an easy target in the meadows.

Väli and Magalhaes specifically paid attention to the records on feeding patterns of a pair of eagles during their breeding season. "The eagle looks like it could catch a big prey, but it doesn't. They merely seize a small mouse or a frog with their beak, carry it to the nest, and that's enough for them," says Väli. This means, however, that birds must fly often from and back to their nests. When there was a growing hatchling in the nest, the researchers expected to see evidence of even more frequent prey deliveries among the older birds: "We did see an incremental increase," said Väli.

The researchers were also interested in observing the parental roles in the lesser spotted eagle during the nestling period. Väli said that in the lesser spotted eagle, as in most raptor species, it is the female who, after incubating the eggs, also looks after the hatchlings. "It has been known that the mother bird begins hunting at the end of June or the beginning of July, after the young are half-grown. We saw this confirmed in the records made by volunteer observers," he said. Thus, although many observed facts about the lesser spotted eagle were already known, the study showed that the data provided by citizen scientists could be trusted. "They really wrote things down as we have expected to find them, at least to some extent," said Väli.

Citizen science has high potential for ecological research in the future

"Above all, our study showed that citizen science is a reliable source of information, and this tool could be useful in different ways. It could be useful in the study of other species and in a different set-up, for example, on a slightly larger scale," Ülo Väli said.

This research confirmed the earlier discoveries on the diet and behavior of the lesser spotted eagle during their breeding season: "We've been sitting in the field hides, peering through our binoculars and taking photographs with long-distance lenses to spot what the birds are preying on. Our survey of the data collected by citizen scientists via webcams reflected the general pattern detected in our earlier studies fairly well," said the senior researcher.

For instance, the crowd-observation of the cowslip primrose is also gaining momentum in Estonia. "Cowslip spotting is an increasingly popular activity worldwide with the data collected continuously increasing," Väli said.

Väli noted, there is nothing new in the idea of nonprofessionals contributing to science. "Modern citizen science is simply the reinvention of an old practice, which has already been promoted by, among others, Eerik Kumari in the middle of the last century," he said. The examples of such a long-term practice in Estonia are, among others, the activities of the Estonian Ornithological Society (Birdlife Estonia) and the Estonian Naturalists' Society (ELUS).

"At the time, it was emphasized that amateur ornithologists could also publish the results of their birdwatching activities in scientific journals", Väli explained, and added that now the emphasis is on people watching and recording their observations, while professionals analyze it further.

Väli also added that it is regrettable only a fraction of professional research is open to the general public: "I believe the accumulated information and serious scientific analysis could be put to a wider use," he said.

Ülo Väli ja Ana Magalhaes have published their research in PLOS ONE.

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