Fossil and subfossil records and recent status of shrikes (Passeriformes: Laniidae) in Bulgaria

A total of 13 Quaternary localities of three recent species of shrikes with a total of 24 bone and bone fragments are reported. They encompass Early Pleistocene (Biharian) to Late Holocene (subrecent) and reveal the wide former distribution of Lanius collurio throughout the country. Eleven localities are situated in the Northern Bulgaria and two – in southern regions of the country. Most of the localities are located in plain and hilly landscapes and only two localities are mountainous. For each species are provided data on the chronostratigraphic distribution, altitudinal distribution and the anatomical belonging of finds. Localities of L. collurio are located between 50 and 130 m a.s.l.


Introduction
Although the oldest fossil record of shrikes (Laniidae Swainson, 1824) has originated from Europe (Late Miocene from Polgardi 2, Hungary, see Mlíkovský, 2002; Middle Miocene from Felsőtárkány-Felnémet, Hungary, see Kessler & Janos, 2012), at present it is believed that the family of shrikes originated in the Australasian region (Josef, 2008). The family's Pleistocene fossil records are abundant in Europe, but most of the localities are concentrated in the southern parts of the continent (Tyrberg, 1998). Shrikes have been well known in the Quaternary in the Balkan states. Bulgaria has one of the richest fossil record regarding shrikes both on the Balkan Peninsula and in Europe.

Results and discussion
Red-backed shrike Lanius collurio Linnaeus, 1758 At present, L. collurio is a migratory species from the southern regions of the boreal zone to the temperate zone in the Western Palearctic. The species inhabits open lands with dry soils and scattered thorny shrub and trees, steppes and semideserts (Harrison, 1982). The 16°C July isotherm limits its breeding range. The red-backed shrike is an indicator for sunny, warm and dry high-grassy habitats (Cramp & Perrins, 1993).
Historia naturalis bulgarica 41 (2020) Status in Bulgaria: in the recent Bulgarian avifauna, the species is breeding and migratory. During migration, L. collurio is common throughout all the country (Ivanov, 2011), except the highest mountain regions.
Fossil records in the Western Palaearctic: fossil remains of L. collurio are known from Austria, Croatia, Czech Republic, France, Germany, Hungary, Moldova, Romania, Ukraine and the United Kingdom (Tyrberg, 1998).

Lesser grey shrike Lanius minor Gmelin, 1788
In the Western Palaearctic, L. minor is a breeding bird in the drier temperate zone. It winters in subtropical to tropical zones in Africa, south of the Sahara Desert (Harrison, 1982). Inhabits "grassy areas with more tall trees, and in more forested areas than the great grey shrike" (Harrison, 1982: 214), forest edges, dry grass steppes and landscapes with scattered trees, parklands and orchards.
Status in Bulgaria: widespread throughout the country mainly in the plain and hilly areas up to 900 m a.s.l. (Ivanov, 2011).

Great grey shrike Lanius excubitor Linnaeus, 1758
At present, L. excubitor is a migrant and resident bird in the Western Palaearctic. It breeds in drier subarctic to tropical zones and winters in temperate to tropical zones. Inhabits partly open areas with scattered trees and tall shrubs from the scrub and forest tundra to the mixed and broadleaf forest, moorland and dry hillsides (Harrison, 1982). Status in Bulgaria: regularly wintering but in small numbers and highly dispersed. Single specimens are found in winter in many regions of the country (Ivanov, 2011). Lanius excubitor is a critically endangered species according to the Bulgarian Red Data Book (Nikolov, 2015).

Conclusions
Skeletal representation indicated that in the collected bone material the most numerous were humeral bones (8), followed by tibiotarsi (3) and mandibles (3). A total of ten skeletal elements were represented in the Bulgarian fossil record.
Obviously, L. minor and L. excubitor were not abundant in the Pleistocene and the (Early) Holocene in Bulgarian localities of the Quaternary avifauna. We can explain that by the underrepresentation of the lesser to medium-sized passerines due to usual common taphonomic reasons. It is important to note that all of the studied localities were former feeding places of the Eurasian eagle-owl Bubo bubo (Linnaeus, 1758), which determines the frequency of shrike bone remains in the deposits. Eagle-owl hunts within a range of 50 km 2 from its nest during the breeding season and sometimes the prey may be captured 5-7 km away from the nesting site or feeding place.
All Quaternary localities (except for Shirokovo for L. excubitor) lie within the present species breeding range. The site of L. excubitor is among the southernmost localities of that species in the Palaearctic (along with the sites in Mallorca, Azerbaijan and Israel, see Tyrberg, 1998).
Although not very numerous, the fossil records of shrikes complete the scanty knowledge on the Pleisto-cene and Holocene paleoenvironment in the region of its localities in Bulgaria. In the surroundings of each of them, the former distribution of the broadleaved scattered trees and tall shrubs and open-grass meadows is confirmed by the established skeletal remains of shrikes.