Population dynamics of five riverbed breeding bird species on the lower Drava River, NE Slovenia

• Published in: Acrocephalus
• Main Authors: Božič, Luka, Denac, Damijan
• Format: Article in Journal/Newspaper
• Language: English
• Published: Walter de Gruyter GmbH 2017
• Subjects: Actitis hypoleucos; Common Sandpiper; Ringed Plover
• Online Access: http://dx.doi.org/10.1515/acro-2017-0008; http://content.sciendo.com/view/journals/acro/38/174-175/article-p85.xml; https://www.sciendo.com/pdf/10.1515/acro-2017-0008

Abstract 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 m 3 /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 ...