1 2 Summary In 2016 most important breeding areas of both population groups of Aquatic Warbler in Ukraine were surveyed. In particular, 6 breeding areas of the Desna- Dnipro population were visited from 30 th May till 4th June (5 evening censuses). Two persons participated in the survey. Monitoring of the Prypiat population groups was held on 14-25 th June, and 10 evening censuses were carried out. During this period, the number of survey participants ranged from 4 to 17 persons. The survey involved 2 ornithologists from Germany, 8 – from Lithuania, 4 – from Poland, 5 – from Ukraine. The censuses covered 435 ha of all 1,090-1,190 ha of suitable habitats in the breeding sites of Desna-Dnipro population, where the surveys were carried out (total area of suitable habitats is 1,180-1,280 ha). 48 males were recorded there. In breeding sites of Prypiat population 724 males were recorded on 2,889 hectares. This is about 49.7% of the total area of suitable habitats in the breeding sites (5,765-5,865 ha), where the surveys were carried out, or ~ 43% of the total area of suitable habitat of the Prypiat population (6,615-6,715 ha). During the survey of the breeding sites of the Desna-Dnipro population hydrological conditions were optimal for most parts of them – they were significantly better than in 2014-2015. Importantly, during April and early May the water level in the AW habitats was significantly lower than during our investigation. Heavy rains during the second half of May led to a rise of the water level in the habitats. This also concerns the vegetation - almost all was not subjected to the winter and spring fires (except for one – UA-04 “Voronky”). In this season we have observed very critical situation in the key breeding sites in Udai valley UA-05 “Dorohinka-Monastyryshche” and Supii valley UA-01 “Vilne- Berezanka” (Halka valley UA-06 “Halka” and Supii valley UA-04 “Voronky” also). The AW number was reduced greatly in these breeding territories. The AW number of six breeding sites (where survey was carried out, without the expected number in UA-07 “Paskivshchyna” and UA-08 “Horodok”) was estimated at 153-220 males. For the third year in a row in the floodplains, where AW of Prypiat population breed, no spring floods occurred. This often leads to burnout of habitats of birds. This was observed in 2014-2015 and 2016. In particular, in the breeding period of 2016 we recorded previous burning of 90-100% of breeding habitats in site UA-16 “Hrechyshcha-Shlapan”, UA-17 “lake Liubiaz”, UA-21 “Sudche”, UA-23 “Naviz- Kolky”. The total number of AW on the four breeding sites was estimated at 32-45 males, whereas in 2014 it was 225-275, and in 2012 – 360-430 males. The water level was well below the ground in the AW habitats of almost all breeding sites. Only in two areas it was optimal – in UA-17 “lake Liubiaz” and UA-24 “Bile-Pisochne”. However, the first site was completely burned in spring and AWs were absent, but the second site was in an optimal state and the number of AW was very high. 3 For the surveyed breeding sites of the AW Prypiat population (evening censuses or, at least, visits during the day period), we estimate the total AW population at 1,857-2,095 males . We can assume that this is the total number of Ukrainian part of Prypiat population, because to automatically add birds from breeding areas that have not been visited would not be correct. It is necessary to take into account the conditions of many breeding areas during the last three years, when habitats were dry and burned. AW were often absent in such areas. Therefore, we can not be sure whether the birds bred in areas that we have not visited. Thus we should not add birds that have been counted in previous years in other sites to the total number for Ukraine. The total AW number in Ukraine in 2016 we estimate at 2,010-2,315 males. We are very grateful to all our colleagues for their participation in the survey of the Aquatic Warbler in Ukraine. And a special thanks to our German and Polish colleagues for the financial support of this research by the German and Polish BirdLife partners (NABU and OTOP). Without that it would have been impossible to perform this survey. 4 Introduction There are two population groups of breeding birds of this species in Ukraine – the Desna-Dnipro and the Prypiat population. In recent years, when surveys of the two groups were held, the number of Ukrainian population was estimated as follows: 3800-4365 males - in 2008, 4000-4750 in 2009, 4200-4900 – in 2010, 3450-4050 – in 2012, 3400-3780 – in 2014, 3050-3375 –in 2015. Terms and Method of Research In 2016 most important breeding areas of both population groups of Aquatic Warbler in Ukraine were surveyed. In particular, 6 breeding areas of the Desna- Dnipro population were visited from 30 th May till 4th June (five evening censuses). O. Iliukha and A. Poluda participated in the survey. Monitoring of the Prypiat population groups was performed from 14 th to 25 th June, and O. Iliukha, M. Khymyn, Y. Korkh and A. Poluda participated in all the 10 evening censuses. In the evening censuses from 16 th -23 rd June, further colleagues from Germany, Lithuania, Poland and Ukraine participated (Annex 2, Tabl. 1 and 2; Annex 3, Photo 1). During this period, the number of survey participants ranged from 6 to 17 persons per evening. AW censuses are conducted with the method developed by the International Working Group on the Aquatic Warbler (Aquatic Warbler Conservation Team, 1999). In the Aquatic Warbler habitats 200 m wide and 1-1.5 km long transects were surveyed. This surveys began 30-40 minutes before sunset. Singing males were counted during sunset because the singing activity of males is very high. The number of males at a site was calculated by extrapolating the results of transect accounts on the entire area of suitable AW habitat at the site. Besides assessing the number of birds in a definite grouping, the state of plant associations and the hydrological conditions of the habitat were determined (pits were dug on the most nesting areas to control the water level). Results and Discussion Desna-Dnipro Population During the survey of the AW breeding areas (30.05.-04.06.2016) hydrological conditions were optimal in most parts of the sites. Importantly, during April and early May the water level was significantly lower than during our investigation. Because of this, some breeding territories were completely burned. Heavy rains during the second half of May led to a rise of the water level in the habitats (Annex 2, Fig. 1). 5 UA-01. Supii valley, area between Vilne and M. Berezanka (Vilne- Berezanka) Aquatic Warbler occupies part of the floodplain of river Supii, which is a tributary of river Dnipro. The whole local population is located in the hydrological zakazniks "Usivskii-I" and "Usivskii-II". This part of the floodplain of Supii river ia a eutrophic sedge marsh. Te total area of AW habitat is about 260 ha (Annex 1, Map 1). The data on the water level in the monitoring area in general show a rather sustainable water regime. As a rule, the water level in the monitoring pits ranged from -3 to +12 cm in May and June. In the first 10 years of observation (since 1995) only in one season (June 2003) the water level in the breeding period was low (-5 cm) (Annex 2, Fig. 2). However, since 2011, there have generally been low levels of water in the breeding season. The water level in water point was +2 cm in June 2010, it was -10 cm in the third decade of May 2011, -6 cm – in the first decade of June 2012, -11 cm – in the third decade of June 2013, -6 cm – in the second decade of June 2014, -9 cm – in the first decade of June 2015. In 2016 (3rd June), the water level was -6 cm. During inspection most of the breeding habitat was wet, but most likely in the middle of May the territory was drier. In this season we carried out evening censuses on two plots in the western part of the floodplain. Our monitoring route is located on the first (northern) plot (40 hectares). Only two males were counted on this territory (Annex 1, Map 1). For comparison, on the same plot in 2015 12 males were registered, in 2014 – 13, 2013 – 22, 2012 – 16. The active expansion of bushes continues on this plot (Annex 3, Photo 2). On the second (central) plot (80 hectares) only 3 males have been counted. In previous years, in this area the number of males was 5-10 times as high. A total of only 5 males was counted on an area of 120 hectares. We can assume that in adjacent areas (southern area of 60 hectares with more water, and an eastern area of 80 ha) 10-15 males do occur. The total number of AW of the whole population group was dramatically low – only 15-20 males (in 2014- 2015 it was 70-80 males, in 2013 – 90-100 males, in 2012 – 80-90 males, and in 2010 it was 140-160 males. UA-02. Supii valley, area near Novyi Bykiv (Bykiv) The AW group occupies the western half of the Supii river floodplain. The whole group is located in the reserve of local importance "Boloto Supii".