Recent changes in the presence status and numbers of ruddy shelduck (Tadorna ferruginea) in the Eastern Balkans

The ruddy shelduck (Tadorna ferruginea) is a species of great conservation importance within its European breeding grounds. Tadorna ferruginea is included in the Red Data Book of Bulgaria (2015) in the category “Critically Endangered”. The species is qualified as “Near Threatened” in EU27 countries as a whole. Recent data from the Balkan parts of the species range indicate its considerable enlargement. During the last 10-year period, the presence status of the ruddy shelduck during winter changed from incidentally wintering in low numbers to regular and even locally abundant wintering species. The numbers of T. ferruginea migrating over the Eastern Balkans increased substantially, especially during autumn. The reasons of these expansion of the species are discussed.


Introduction
The ruddy shelduck (Tadorna ferruginea Pallas, 1764) has a small natural breeding range in Europe, restricted to the southernmost parts of Russia and Ukraine, Southern Moldova, eastern parts of Romania (Dobroudzha), Bulgaria, Greece and European Turkey (Nankinov et al., 1997;Hagemejer & Blair, 1997;Birdlife International, 2004). It is a species of great conservation importance in its European breeding grounds and is included in the Red Data Book of Bulgaria in the category "Critically Endangered" (Zehtin-djiev et al., 2015).The species is qualified as "Near Threatened" in EU27 countries (Birdlife International, 2015). Tadorna ferruginea was considered as a breeding migratory species in Bulgaria, wintering in the country as an exception (Zehtindjiev et al., 2015). A steady decrease in population numbers for the period 1990-2010 was reported: from 50-200 breeding pairs (Kostadinova, 1997) to 70-90 pairs (Nankinov et al., 2004), 40-80 pairs (Ilieva et al., 2007) and further to only 15-20 pairs (Zehtindjiev et al., 2015). During the last 20 years a program for restocking of the local population was implemented at the Biological Experimental Station Kalimok (Institute of Biodiversity and Ecosystem Research of the Bulgarian Academy of Sciences), in an attempt to stop the negative trends in numbers of this species.
In Greece, a small nesting population of the species is confined to NE Thrace and some of the Aegean Islands, with a total of 15-40 breeding pairs in the 90-ties of the XX-th century (Handrinos & Akriotis, 1997;Birdlife International, 2004).
Typical wintering grounds of the species in the western parts of its distribution lie in Turkey, Syria, Palestine, North Egypt, Iraq, Iran, Azerbajdzjan (Hue & Etchecopar, 1970;Cramp & Simmons, 1977). The ruddy shelduck is a migratory bird on the Balkan Peninsula with small numbers wintering in Greece (Cramp & Simmons, 1977). Winter numbers recorded during the mid-winter counts of waterfowl in Bulgaria have been in the range of 0-15 individuals (Kostadinova, 1997). According to Michev & Profirov (2003), in the period 1977-1996 only five ruddy shelducks have been recorded to winter in the country during these counts. The same authors mention the first more numerous flock wintering in Bulgaria: 16 individuals (ind.) has been recorded in January, 1999 in the Danube River between Ruse and Silistra. A flock of 14 ind. was observed in the Durankulak Lake, NE Bulgaria, on 29.12.2006 (Simeon Gigov -https://ebird. org/view/checklist/S35057644).
In Greece, the species winters regularly but in low numbers (Bauer et al., 1969;Handrinos & Akriotis, 1997). Occasionally, bigger flocks of tens of birds have been recorded during winter and migration periods, mainly in the coastline lakes of Thrace: in the delta of the Mesta (Nestos) River -up to 150 ind. on 15.01.1973, in the delta of the Maritsa (Evros) Riverup to 68 ind, in the Ismaris Lake -up to 25 ind. (Handrinos & Akriotis, 1997).
Migration of the species over the Eastern Balkans during the 90-ties of XX-th century was considered as "almost unnoticeable" and took place in spring from the end of February until April and in autumn -from the end of July to November (Nankinov et al., 1997).
New data collected for the present study, including terrain observations and literature sources, reveal considerable changes in status, distribution and numbers of the ruddy shelduck in the Balkan countries during the last ten years.

Material and methods
The study area included the major part of the Balkan distribution of the ruddy shelduck -Bulgaria, the easternmost part of Romania and continental Greece (the Aegean coast of the Thrace Province).
The data were collected during the period 2008-2020. Data on the status and distribution of the ruddy shelduck in the Balkan countries before 2008 had already been presented in the existing scientific literature (Nankinov et al., 1997;Handrinos & Akriotis, 1997;Ilieva et al., 2007;Zehtindjiev et al., 2015). Out of 30 formerly known localities, 20 were visited on one or more occasions during the period of the present study.
Inland wetlands were specifically investigated during the breeding period of the species -April-June. We chose wetlands offering typical habitat for the species, i.e. small-to medium-sized artificial or natural wetlands among steppes, natural grasslands or agricultural lands with bare shores and suitable places for earth or rock hollows in the vicinity (e.g. limestone or loess slopes or cliffs, often along small rivers or in dry river valleys). All types of wetlands were visited during migration and winter periods.

Bulgaria
During the period of the study, a considerable enlargement of the breeding distribution of the ruddy shelduck in Bulgaria was recorded (Fig. 1). We found that the occupied territory in North-eastern Bulgaria was enlarged in southern direction. In South-eastern Bulgaria the newly found localities lay in western and south-western direction from the previously known distribution. Concrete new localities were as follows: North-eastern Bulgaria  According to the existing published and newly obtained data on the breeding numbers of the species, the size of the Bulgarian population of the species could be expected to be between 80 and 120 breeding pairs. The ruddy shelduck was distributed in a total of 49 UTM squares, in 19 of them (38.8%) the species was found for the first time after 2008. In 12 UTM squares the species was found before 2008 and confirmed later by us. In the rest 18 UTM squares the spe-cies was found before 2008 and not confirmed later by us or other authors.

Romania
According to the data presented for the report under article 12 of the European Bird Directive (2008-2012), the ruddy shelduck was found during the breeding period in 58 ETRS 10x10 squares in Dobrudzha, an area between the Lower Danube River and the Black Sea coast, and in one ETRS square to the west of the Danube River, with a total population of 40-70 breeding pairs (http://pasaridinromania.sor.ro/Califar-rosu; https://circabc.europa.eu/sd/a/68b0ea7d-3a11-4a12-9eb4-4308c39d7de8/RO_A12NatSum_20141031. pdf). In the past its breeding numbers across the country were lower -20-25 pairs (Vasiliu, 1968).

Discussion
The winter status of the species has changed significantly during the last ten years. Before 2008, the species was irregular wintering species in Bulgaria and regular but not numerous winter visitor in Northern Greece. In Burgas wetlands for the period 1996-2002 the maximal number of the species during winter was 5 ind., all at Atanasovsko Lake in 1999 (Dimitrov et al., 2005). In Maritsa (Evros) River Delta, winter numbers of the ruddy shelduck were reported to be 42-239 ind., according to the standard data form of the special protected area (SPA) Delta Evrou. (http://natura2000.eea.europa.eu/Natura2000/SDF. aspx?site=GR1110006). Flocks of over 1000 birds as recorded in December 2017, in Maritsa River (Evros) delta (present study), have never been reported from the Balkan Peninsula. Nowadays, the ruddy shelduck can be qualified as regular winter visitor in Eastern Bulgaria and Eastern Romania and numerous wintering species locally in NE Greece.
Breeding numbers and distribution of the species also showed clear positive trend. Many of the formerly (in the period 1980-2000) abandoned areas have been reoccupied recently, such as many locations in NE Bulgaria. In the 80-ties of XX-th century the westernmost distribution of the ruddy shelduck in the Danube River Plain reached Nikopol and Brashlyanitsa, Pleven District (Boev, 1983;Botev & Peshev, 1985). If the current positive trend continues, soon we could expect reoccupation also of these areas in the Central Danube River Plain. Additionally, some new areas were occupied recently by the species in SE Bulgaria, such as Yambol District and some locations in Haskovo District. Former data about the presence of the species in these regions are lacking or they do not refer to confirmed breeding but only to observations of pairs during the breeding period (Ilieva et al., 2007).
Recently, the numbers of the ruddy shelduck both during autumn and spring migration has increased.
Monthly monitoring at Burgas wetland complex for the period 1996-2002 recorded maximal counts of up to 29 ruddy shelducks during the spring migration and 15 ind. during autumn migration (Dimitrov et al., 2005). The highest number for that study was reached in June in Atanasovsko Lake -35 ind. These numbers are significantly smaller as compared to the numbers recorded during the present study at the same locality. The greatest increase was recorded after 2016 and to a greater extent during autumn migration period.
However, the origin of the wintering and migrating ruddy shelducks across the Eastern Balkans remains unclear but we suppose that most of them come from the breeding populations of Ukraine and Southern Russia. Alternative hypothesis can be that flocks from Asia Minor also contribute to the observed picture, especially in forming the wintering population in Greece and SE Bulgaria.
What are the possible explanations of the increase of the numbers of the breeding, migrating and wintering ruddy shelducks on the Eastern Balkans? Increase of the breeding numbers and distribution of the ruddy shelduck throughout Eastern Balkans could be explained by some recent trends. Much milder and snowless winters in the region during the last 20 years allow many of the local birds to stay close to their breeding grounds. The increase of the birds spending winter in the Balkan states is obvious. Shorter migration distances decrease the chance of mortality of birds along the migration route. The rearing of captive ruddy shelducks at the Kalimok Biological Experimental Station and releasing them in the wild is another positive factor that, without any doubt, contributes to the species numbers, at least at local level.
For the increase of migration flocks using Balkan routes the main reason could be the increase of the breeding populations in the Balkan countries, Southwestern Russia, Ukraine and possibly in Asia Minor. During the period 1980-2000, there was a significant increase in the breeding population of the species in southern parts of European Russia, e.g. Stavropol District, Lower Volga River, Don River Valley and Western Manich Lake (Krivenko & Vinogradov, 2001). In Ukraine some areas where the species has been extinct in the past, nowadays are being reoccupied again: for example Harkov Region, where the species started to breed after long period of extinction (since 1997) and its number reached 40-45 pairs in 2014 (Banik, 2014), but also in Lugansk Region and other parts of the country (Vetrov & Litvinenko, 2014). The increase of the ruddy shelduck numbers and distribution in the western parts of its breeding range is explained with the shift of the traditional moulting sites from east (Kazakhstan) to west (in Southern Russia, Manich-Gudilo Lake system) because of drought of some key wetlands in Central Asia (Banik, 2014). The same author deny the possibility that the increase of the ruddy shelduck population is a consequence of the increase of the semi-wild population of "Askania-Nova" Nature Reserve (Ukraine) and gives a proof from the numerous ringing recoveries revealing that birds hatched there are almost entirely sedentary. The longdistance records of ruddy shelducks from that population are very rare and are reported from Russia, Azerbaijan and Georgia (Zubko et al., 2001).