Numbers, distribution and nest site characteristics of Jackdaw Corvus monedula in Slovenia and its conservation status

Abstract

In 2008, a coordinated census of Jackdaw Corvus monedula was carried out to assess breeding population, distribution and nest site selection in Slovenia. Data collection continued for unsurveyed areas in the 2009-2011 period, including information on former colonies and threats. A total of 663-794 Jackdaw pairs were recorded at 86 sites, while total Slovene breeding population was estimated to be in the range of 700-900 pairs. Over one third of pairs were recorded in Central Slovenia, notably the largest city Ljubljana (20.8%), followed by almost a quarter in the Podravje region. Most colonies numbered between 2 and 5 pairs, the largest occupying the Bežigrad district of Ljubljana (82-87 pairs). Large-scale density in geographically more or less uniform areas ranged from 3.65 pairs/10 km2 in the Sava plain to 0.15 pairs/10 km2 in mostly mountainous area in northern Slovenia. The majority of Jackdaws selected buildings for nesting (82.2% of pairs), while nesting in trees occurred less frequently (14.7%) and was almost entirely confined to the two easternmost regions of Slovenia. Nesting in cliffs was recorded at just two sites in Slovene Istria (3.1%). Average colony size differed significantly in relation to nest site type, with colonies in rock walls being on average the largest (median = 9.5 pairs), followed by colonies on buildings (6) and those in trees the smallest (3). Among pairs nesting on buildings, multi-storey residential buildings predominated (34.2%). A substantial percentage of population nested also on churches and tower blocks (14.4% and 13.5%, respectively). The highest percentage of pairs utilised holes in roofs (26.9%), followed by eaves (18.0%) and chimney pots (14.7%). Tree-nesting pairs occupied mostly small woods situated in open agricultural landscape. The most commonly used tree species was Beech Fagus sylvatica (53.1% of pairs) which hosted 14 of the total 16 forest colonies. For Jackdaws nesting in urban parks and avenues, plane trees Platanus sp. were the most important (30.6% of pairs). Their population stronghold was in lowlands, with 88.1% of pairs recorded at elevations under 400 m and the highest living colony in Slovenia at 578 m a.s.l. Jackdaws occurred on at least 54 specific sites in the past but became extinct there or declined severely by the time of this study. A minimum of 217-254 pairs were estimated lost at these sites, constituting a decline of 24% in c. 10-20 years. According to the IUCN criteria, Jackdaw would qualify as Vulnerable (VU) on the Red List of Slovenia. The commonest known cause of extinction/decline is renovation of buildings, a threat that is projected to escalate in the near future.