Most migratory birds cross Europe using two main routes: the East-Atlantic flyway is used by birds from Eastern Canada, Greenland and Western Europe, which pass to Africa through the Strait of Gibraltar, while the Pontic-Mediterranean flyway gathers birds from Central- and Eastern Europe and the western part of Asia. Songbirds avoid flying over large bodies of water; thus, they follow the Black Sea coast while crossing Romania. Chituc Spit is a sandbank located south of the Danube Delta, wedged between Lake Sinoe and the sea, and is one of the last of wild beaches in the country. Due to the NE-SW orientation and the positioning between two large water surfaces, the spit acts as a funnel for migrating songbirds, but it is widely used also by other migratory species. The fully protected status within the Danube Delta Biosphere Reserve voids this place from human impact, and allows birds to feed and rest undisturbed throughout the migration period.
After an absence of 17 years, Milvus Group organizes every autumn since 2014 a ringing camp on Chituc Spit, with the aim of researching bird migration in the area. The ringing activity runs for 14 to 17 weeks, from mid-July to early November. The mist-nets are located in three types of habitats: in the reed bed (180 m), in shrubs (110 m) and in semi-open habitat (80 m), and sum up to a total length of 370 m. Some of these nets were added in the last two years, but the data collected in different years can be compared by applying some correction methods (e.g. correction to the total length of nets).
The results of the camp from 2019
We carried out ringing activities for 99 days, between July 21 and October 26. During this period, the teams composed of 11 ringers and 89 volunteers, marked a staggering number of 19.927 birds, which represents an absolute record for the camp and also for Romania, since no other continuously running ringing activity had produced so many ringed birds. The busiest week in camp’s history was between October 13-19, 2019, when we ringed a total of 4.231 individuals. A new daily record was also established by ringing of 876 birds on October 20, 2019.
Of the 112 ringed species this year, the five most abundant species captured were the robin (Erithacus rubecula, 2.796 individuals), the blue tit (Cyanistes caeruleus, 2.696 individuals), the red-breasted flycatcher (Ficedula parva, 2.115 individuals), the sedge warbler (Acrocephalus schoenobaenus, 1.684 individuals) and the bearded reedling (Panurus biarmicus, 1.072 individuals). Two national rarities were ringed in the last two weeks of the camp: a red-flanked bluetail (Tarsiger cyanurus, 3rd national observation) and a Pallas’s leaf warbler (Phylloscopus proregulus). Another Pallas’s leaf warbler was observed near the camp but it was not captured.
Regarding the international recaptures of the camp, we added to the camp’s list an adult reed bunting (Emberiza schoeniclus) ringed in Greece on November 1, 2018 and recaptured at the camp on September 5, 2019, and a great reed warbler (Acrocephalus arundinaceus) ringed by us on August 17, 2019 and recaptured in Durankulak, Bulgaria on September 7. Thanks to our colleagues from the “Prof. Dr. Ioan Borcea” Marine Biological Station from Agigea we have two new national recaptures also: they recaptured on October 13 a blue tit ringed by us two days earlier, while we recaptured on October 19 a blue tit ringed at Agigea on October 15.
Regarding our local recaptures from this year, we mention a ruddy turnstone (Arenaria interpres) ringed in August 2014 and photographed near the camp on August 9, 2019; a sanderling (Calidris alba) ringed in September 2016 and a reed bunting ringed in July 2015.
The results of the camp from the last 6 years
In the 593 days of ringing activity between 2014 and 2019, we ringed a total of 85.556 individuals of 161 species, the most abundant species being presented in Fig. 4. The most emblematic species of the camp remains the red-breasted flycatcher, because, besides being the most abundant species of our camp, as far as we know, no other ringing camp catches as many individuals as we do on Chituc Spit.
Because the number of days of ringing and the total length of the mist-nets used varies between 2014 and 2019, in Fig. 5a we present the annual totals divided by the lengths of the nets and the days of activity of each year (i.e. thus controlling for these differences), while the exact values are shown in Fig. 5b.
The pentade is a commonly used unit of measurement to present data collected during migration, that represents the number of individuals captured from a particular species in 5 consecutive days. We present below charts with the migration dynamics of several bird species that migrate predominantly in shrub habitats (the length of these nets has been relatively constant throughout the six seasons of study), grouped in such pentades:
Between 2014 and 2019, the birds ringed by us on Chituc Spit four individuals have been recaptured in Romania, two in Bulgaria, two in Italy, one in Turkey while other four individuals were recaptured in Israel. During the ringing activities we have recaptured or resighted birds from Romania, Hungary, Poland, Cyprus, Greece and Israel, one individual from each country.
The data gathered during the six years of ringing represent a solid basis for monitoring the migratory numbers of the species that cross Chituc Spit. In order for the monitoring to be representative, it must be repeated periodically with the same effort (i.e. the same working period, the same surface of nets placed in an always identical configuration). Thus, carried out in the long term, such monitoring aids a real and useful image about the migratory population size, and implicitly, the populational changes in the breeding area of these migratory species.
We hope to continue the ringing activity in the forthcoming years, studying the autumn migration of songbirds which are on their way to their wintering quarters. We thank all the ringers and volunteers for their effort and professionalism, exhibited at the camp from the early hours of the day until dark.
The ringing camp was financially supported in 2019 by S.C. Kék Hal S.R.L., the Association of Ecology Students from the “Lucian Blaga” University of Sibiu and by Jenica and Cornel Cotorogea, for whose contribution we are deeply grateful.
We are also grateful to the Administration of the Danube Delta Biosphere Reserve, especially to the governor, Mr. Catalin Țibuleac, for the institutional support of our research activity.