Population dynamics of the White Stork Ciconia ciconia in Slovenia between 1999 and 2010
Between 1999 and 2010, an annual census of the White Stork Ciconia ciconia breeding population was carried out in Slovenia using standardised methods. The Stork's population was concentrated in the NE and SE parts of Slovenia. In the 1999-2010 period, the breeding range of its population in Slovenia expanded in NW direction (the Savska ravan region), in SW direction (the Notranjsko podolje and Pivško podolje regions), but the species also colonized a part between Central and SE Slovenia (Dolenjsko podolje). Between 193 and 240 pairs were breeding during the study period, 209 pairs on average (HPa). The largest number of breeding pairs was recorded in 2004, the smallest in 2005. During the study period, breeding pairs (HPa) occupied 350 discrete nests in total. Average number of breeding pairs that raised juveniles (HPm) was 161. The highest fecundity was recorded in 2004, when 534 juveniles (JZG) fledged, the lowest in 2006, with only 219 fledged juveniles. On average, 414 juveniles fledged per year. The breeding pairs' (JZa) average breeding success in these 12 years was 2.02, the highest in 2000 (2.41), the lowest in 2006 (1.09). Average breeding success for the successful breeding pairs (JZm) was 2.57. The highest was in 2007 (2.94), the lowest in 2006 (2.07). The largest number of breeding pairs in 2004 and 2008 can be explained by the favourable fecundity in the population in 2000 and 2004, as juveniles become sexually mature at the age of 3-5 years, and at that age they generally return to the breeding grounds for the first time. The lowest number of breeding pairs and poor breeding success in 2005 and 2006 was caused by late arrival of White Storks to the breeding grounds and by unfavourable weather conditions during the breeding period. The pattern of nests placement did not change generally during the last 12 years. The largest proportion of nests was positioned on various kinds of poles (81%) and on chimneys (18%). In total, 27 area surveyors and 239 assistants helped in census realisation.
An overview of the long-term (1980–2019) population development of colonial Laridae species in continental part of Slovenia, their nest sites at anthropogenic water bodies, and various conservation measures with special focus on Common Tern Sterna hirundo along the Slovenian/border part of the Drava River is given. Breeding of these species occurs only on the westernmost fringes of the Pannonian plain, on lowland floodplains of the main rivers of the Danube Basin. Altogether, breeding of Common Tern and Black-headed Gull Larus ridibundus was recorded at 11 and 10 sites, respectively. Lake Ptuj is the single site with mixed-species colony residing there in all years of the study period, while at Ormož (two sites) it was established during the early 1990s in the Slovenian territory but moved completely to the Croatian side by the second half of the 2010s. At all other sites, a suitable breeding habitat became available or was provided by management in just a few years, or created only recently. The percentage of Common Tern national population breeding in continental Slovenia was usually well above 50% throughout the 1980s and 1990s (52–136 pairs), while in the last 16 years (77–258 pairs) it ranged between 40.8% and 69.0%. Breeding of Black-headed Gull remains largely limited to continental Slovenia. Overall, continental populations of both species in the last few years have been substantially higher compared to the most of the study period. Long-term trends were estimated as a moderate increase for Common Tern and a strong increase for Black-headed Gull. Since 2006, the Mediterranean Gull L. melanocephalus has been a regular breeder at Lake Ptuj (up to 28 pairs), the only such site in Slovenia. Three general types of conservation measures implemented at different nesting locations are described in detail: (1) measures to create/increase the total surface of breeding habitat – the construction of new breeding structures, such as artificial islands and nesting rafts, (2) measures to maintain and enhance breeding habitat through recurring management activities, and (3) measures aimed to increase chick/nest survival and improve breeding success.
In 2006–2017, annual censuses of breeding bird species regarded as indicators of natural rivers were carried out on the 38.9 km long lowland stretch of the Drava riverbed between Maribor and Zavrč with altered flow regime due to the operating hydropower plants. Gravel bar habitats were surveyed in four years of the study period by combining orthophoto analysis and analysis of field photographs. Effects of gravel bar management were evaluated based at 20 locations. The Little Ringed Plover Charadrius dubius occurred on 39.8% of the gravel bars, but most were occupied only in a few years and held just one breeding pair. Low numbers between 2009 and 2012 (< 30 pairs) were followed by a steep population increase from 2014 onwards to a maximum of 66–73 pairs (1.7–1.9 p/km). Such population dynamics was attributed to the lack of large discharges (>500 m3/s) and consequent overgrowing of riverbed in the first part of the study period, while the increase in the second part was due to the creation of extensive shingle areas (from 20,6 ha in 2009/10 to 37,8 ha in 2014) by the extreme flood in early November 2012, subsequent regular occurrence of large discharges outside the breeding seasons and large-scale removals of woody vegetation. Breeding population of Common Sandpiper Actitis hypoleucos remained at a rather similar low level (<20 p) during most of the period studied after an initial decline, and did not reflect changes in the overall surface area of riverbed habitats. Contrary to the general situation, the number of breeding pairs on gravel bars subjected to management increased several-fold. Maximum number of pairs on these bars was reached up to four years after the initiation of management measures, as only then the optimal mosaic of early successional stages interspersed with shingle areas developed at main sites. The species was widespread only on lower part of the Drava. Kingfisher Alcedo atthis was fairly widely distributed along the riverbed, but occurred in rather low densities throughout (c. one pair on 2–3 km of the studied riverbed on average), probably as a result of limited bank erosion and consequent overgrowing/lack of suitable nest sites. The population was estimated as stable with effects of harsh winter conditions on breeding numbers in some years. The majority of nest holes were excavated in eroded river banks along the main river channel (77.8%), followed by similar sites located in mouth areas of small tributaries of the Drava (14.8%). Regular breeding of Sand Martin Riparia riparia since 2012 (up to 259, mostly at only one location annually) was almost exclusively the result of the annual artificial nest site preparation programme. Fairly large gravel bar-breeding population of White Wagtail Motacilla alba, monitored since 2013 and predominantly ground nesting in sparsely vegetated areas, seems unusual considering the prevalent breeding habits of the species at the European scale. Conservation implications and guidelines for future management efforts are discussed.
In 2012 and 2013, the selection of foraging habitats and the diet of the Hoopoe Upupa epops were studied in the Goričko area, where a significant population decline of the species has been recorded in the past 15 years. Goričko is an area with a well-preserved traditional mosaic-like agricultural landscape very rich in biodiversity which, however, is disappearing. The diet was determined using automatic camera recordings of prey brought to chicks by parents. Mole crickets Gryllotalpa gryllotalpa were the most dominant prey (35.4% frequency and 81.3% biomass of prey), followed by Scarab beetles larvae Scarabaeidae, caterpillars Lepidoptera larvae and True flies Diptera. Feeding frequency was highest in the period of most intensive chick growth (between 8 and 21 days of age). Selection of foraging habitat was researched by observation of birds during foraging. Hoopoes foraged mostly in mown meadows and grassy courtyards and, to a lesser extent, on sandy cart tracks and road edges. These habitats were characterized by low vegetation and patches of bare ground that enabled Hoopoes to forage efficiently. Home range size was determined using minimum convex polygons. The maximum home range size was between 42.9 and 57.7 ha, while the percentage of foraging habitats within the home range did not exceed 18%. Based on our results, we propose the following measures for effective Hoopoe conservation in the area: maintaining the present range of existing unimproved meadows, stopping the conversion of meadows into fields, restoring fields to meadows, prohibiting the use of pesticides targeting Mole crickets.
Due to numerous bird surveys in the past 20 years, the avifauna of Goričko is relatively well known. For some species, the very first national ecological researches were conducted in this area. The article summarizes all bird surveys so far. It presents population trends of farmland species which is one of the most threatened bird groups in Europe. Most of the qualifying species of this habitat that are protected within the Natura 2000 network have suffered a decline at Goričko, specifically Quail Coturnix coturnix, Scops Owl Otus scops, Hoopoe Upupa epops, Woodlark Lullula arborea and White Stork Ciconia ciconia. The number of breeding pairs of the latter has not changed, but its fecundity has decreased. Furthermore, populations of other farmland bird species have decreased, for example Skylark Alauda arvensis, Stonechat Saxicola rubicola, Serin Serinus serinus and Common Linnet Linaria cannabina, as well as butterfly populations and tracts of grassland habitat types. National agricultural and nature conservation policies are evidently inefficient in protecting the biodiversity of Goričko. The most probable cause for bird population decline is agricultural intensification, which manifests itself at Goričko as disappearance and intensification of meadows, land consolidation, degradation of traditional orchards and use of pesticides. As a result of land consolidation hedges, uncultivated strips between fields, individual trees and bushes and minority habitat types are disappearing, whereas the surface of arable fields is increasing. Nature conservation measures performed by the Public Institute Goričko Nature Park with the support of DOPPS – BirdLife Slovenia volunteers seem to be efficient, but are spatially and temporally constrained. For this reason, they cannot serve as a substitute for insufficient systemic financing which could be improved by substantive and financial reform of the agri-environmental scheme. Currently, a negligible percentage (1% in 2016) of Goričko is covered by agrienvironmental scheme measures with positive influence on qualifying species and habitat types. As a consequence, only an insignificant share of subsidies from the Rural Development Plan is used for nature protection at Goričko. If the system of agricultural subsidies remains unaltered, no improvement of the conditions for bird conservation at Goričko can be expected.