Sympatric wintering of Red Kites and Black Kites in south-east Europe

Abstract

We characterized the spatiotemporal activities in winter grounds of the tagged Red Kites Milvus milvus originated from Austria, Czech Republic and Slovakia and wintering in southeast Europe. Birds arrived to winter grounds in Hungary, Croatia, and Greece from 10 July to 12 December (median 22 October) and departed from winter grounds between 14 February and 22 May (median 14 March), thus staying at winter grounds from 121 to 229 days (median 145, mean 161±43 SD). If we regarded kernel density estimate 80% (area of main foraging and roosting activities) as the best indicator as to the size of home range, we revealed that the size of a home range for Red Kites staying at one place through the entire winter was from 10 to 108 km 2 (median 72, mean 60±36 SD) and that the size of home range for birds with local shift(s) in winter grounds was from 344 to 620 km 2 (median 434, mean 466±115 SD). We found not only Red Kites at these places but often also Black Kites Milvus migrans. The numbers of Black Kites wintering together with Red Kites were higher than the number of Red Kites at all Greek winter grounds. At winter grounds in Hungary and Croatia, the number of Black Kites was lower than the number of Red Kites or Black Kites were wholly absent. Sympatric occurrences according to only direct observations of wintering Red and Black Kites were found also in some other locations in Bulgaria, Croatia, Greece and Hungary.

Age, landscape, and arrival date explain ranging behavior of wintering red kites in southwest Europe

“…Despite the well-documented use of urban areas by kites (Knott et al 2009;Literák et al 2017Literák et al , 2019aPanter et al 2020), urban land cover was not a predictor of kite winter space use in our study. This may be an artefact of the large-scale approach of our study because urban land cover constituted a very small proportion of the landscape relative to more open and closed cover types.…”

“…Food is the predominant limiting resource for over‐wintering raptors, with concentrated, high‐quality food resources during winter well‐documented to negatively predict raptor home range size (Kenward 1982, Linkhart et al 1998, Tornberg and Colpaert 2001, Rolando 2002, López‐López et al 2014). Although over‐wintering kites are not strictly territorial, as evidenced by communal roosting (Literák et al 2019 a , Panter et al 2020), threshold group sizes at roosts may mediate acceptance of incomers, and earlier arrivals are more likely to secure areas with rich, concentrated resources, potentially defending these against intruders while foraging. Late arrivals, conversely, will have less choice about where to over‐winter and will consequently be more likely to inhabit less optimal habitats with sparser and more widely distributed resources, resulting in greater ranges.…”

“…Our core area results support the general patterns of age‐related differences identified by previous researchers (Kenward et al 1981, Marquiss and Newton 1981, Rolando 2002), where 1 cy bird core areas were larger than those of older conspecifics. This likely reflects winter site fidelity around areas of high resource availability or communal roosting opportunities (Literák et al 2019 a , Skyrpan et al 2020).…”

“…We tagged all birds with 20-g Saker H loggers (Ecotone, Gdynia, Poland) weighing on average 2% of the kites' body mass. We fitted loggers onto the back of the birds and secured them with a 6-mm Teflon ribbon harness encircling the body in 2 loops around the base of the wings and joining in front of the breastbone following similar methodology to Literák et al (2019aLiterák et al ( , 2019bLiterák et al ( , 2019c. The loggers operated in GPS-GSM systems and received signals every 3 hours depending on signal strength.…”

“…Northern breeding populations tend to be migratory, wintering in 3 key regions of southwestern Europe: the Iberian Peninsula, Italy, and the Pyrenean region of southern France (Evans and Pienkowski 1991, Viñuela 1997, Ferreira et al 2015, Raab et al 2017). They occasionally also over‐winter as far east as Greece (Literák 2017, 2019 a ; Maciorowski et al 2019; Panter et al 2020). Southern populations are mostly resident within the Mediterranean region (Knott et al 2009, Crespo‐Luengo et al 2020) because of milder climates and sufficient local resources available for over‐winter survival (García et al 1998).…”