https://orcid.org/0000-0002-4017-158X
Abstract
The winter months are an important part of the year for raptors as survival throughout this period is critical for the succeeding year’s population recruitment. We reveal novel insights into the wintering of kites (Milvus spp.) on the Mediterranean island of Crete, Greece. We use a combination of 1) direct field observations, 2) online photograph searches and 3) analysis of satellite telemetry data from a tagged hybrid Red Kite × Black Kite (Milvus milvus × M. migrans migrans). The number of observations of wintering kites has increased since 1998. The wintering of numerous Black Kites with morphological features of both subspecies (M. migrans migrans and M. migrans lineatus) and a hybrid Red Kite × Black Kite is a new phenomenon on Crete.
Introduction
Across Europe, there are two native kite species of the genus Milvus, namely the Red Kite (Milvus milvus) (Linneaus 1758) and the Black Kite (Milvus migrans) (Boddaert 1793). The Red Kite is experiencing population declines and it is listed as Near-Threatened on the IUCN Red List of Threatened Species (BirdLife International Citation2018). In the autumn northern European populations undergo short-distance migration and winter in southern Europe including France, Italy and the Iberian Peninsula. Southern European populations tend to be resident all year round (Cramp & Simmons Citation1980; Génsbøl & Thiede Citation2008; BirdLife International Citation2015; Literák et al. Citation2018, Citation2019a).
Black Kites of the nominal subspecies Milvus migrans migrans (Boddaert 1783) (Western Black Kite) breed in the Western Palearctic and Central Asia (Ferguson-Lees & Christie Citation2001) and adopt a different migration strategy than Red Kites by wintering in sub-Saharan Africa and the Middle East (Ferguson-Lees & Christie Citation2001; Panuccio et al. Citation2013). Few Black Kites remain and winter in Europe specifically in the Mediterranean region (Sarà Citation2003; Literák et al. Citation2017). Recent observations suggest that Black Kites with morphological characteristics of the subspecies Milvus migrans lineatus J. E. Gray, 1831 (Black-eared Kite) which are native to Siberia and Japan (often referred to as Eastern Black Kites) are increasing in Europe as well as during the winter months (Ferguson-Lees & Christie Citation2001; Kralj & Barišić Citation2013; Forsman Citation2016; Skyrpan & Literák Citation2019).
Red Kites and Black Kites have the ability to hybridise (Literák et al. Citation2019b). However, due to the large differences in migration strategies between the species, the wintering behaviour of hybrids remains unknown.
To date, there has been minimal research focusing on the wintering of kites on the Mediterranean island of Crete, Greece (Panuccio et al. Citation2019). The aim of this study is to provide an overview of current occurrences of kites wintering on Crete using a combination of 1) direct field observations at key landfill sites and elsewhere on Crete, 2) online photograph searches and 3) analysis of the movements of a hybrid Red Kite × Black Kite tagged with a satellite telemetry logger.
Methods
Identification of kites was based on previously described morphological characteristics (Ferguson-Lees & Christie Citation2001; Forsman Citation2016; Karyakin Citation2017; Skyrpan & Literák Citation2019).
We collated direct field observations of kites by local birdwatchers over 22 winters from 1998 to 2020. Following this, we then supplemented these observations by performing a series of direct field observations between 19 and 21 January 2020 at three landfill site locations on Crete. Landfill sites used by kites were identified based on the latest roost locations obtained from a tagged hybrid Red × Black Kite (see below).
Manual online surveys of kite photographs were conducted targeting ornithological Facebook groups using an in-built search function following a similar search method described by Panter and White (Citation2020). The following key-words were used to identify appropriate Facebook groups: “birding Crete”, “birdwatching Crete”, “Crete ornithology” and “birds of Crete”. Data for Facebook posts containing photographs of kites occurring on Crete during the winter were collected. We defined “winter” as any date between 1 November until 28 February. We supplemented our online search by performing manual searches from BirdGuides (www.birdguides.com) and eBird (www.ebird.org). Photographs ranged from 25 November 2014 until the end of January 2020 as prior content was unavailable.
Additionally, we analysed satellite telemetry data from a hybrid Red Kite × Black Kite female (sex was determined by DNA analysis; Suh et al. Citation2011) tagged as pullus in the natal nest, near to Velké Raškovce in Slovakia on 26 June 2019. The parents of this young bird were a female Red Kite and a male Black Kite confirmed by direct observations and documented by photographs. The bird was tagged with an OT-E25B-3 G logger (20 g, Ornitela, Lituania) fitted on to the back of the bird and secured with a harness consisting of 6 mm Teflon ribbon encircling the body by two loops around the base of the wings joining in front of the breast bone; following the same method as Literák et al. (Citation2019a, Citation2019b). The logger functioned in Global Positioning System/Global System for Mobile Communication (GPS/GSM) systems. GPS locations were sent via SMS text messages by local mobile operators to the Ornitela Centre in Lithuania where they are saved and archived. GPS locations were received every 10 minutes. Analysis of the satellite telemetry data was conducted using a GIS in the software ArcGIS Desktop 10.7.1. with the Spatial Analyst and Home Range Tools extensions (ESRI, Redlands, USA).
Pearson’s Correlation Coefficients were used to test for significant linear correlations between number of observations over time in R (R Core Team Citation2019).
Results
From the long-term field observations, a total of 153 kites were recorded wintering on Crete (). Of these Black Kites comprised 98% of all recorded individuals. The largest number of kites recorded occurred during the 2019/2020 winter, where 61 Black Kites were observed comprising 40% of all recorded individuals over the 22 year period.
Table I. Locations and number of individual wintering kites complied from long-term field observations from 1998 to 2020.
Over a three-day period in January 2020, 157 kites were recorded at the surveyed landfill sites (). Some 68 Black Kites, many of which had features of Milvus migrans lineatus (), two Red Kites and our tagged hybrid Red Kite × Black Kite (OT005) were observed ().
Table II. Locations and number of individual wintering kites observed during direct field surveys at three landfill sites on Crete in January 2020. *Hybrid (Milvus milvus × M. migrans migrans).
Figure 1. (a) A group of perching kites in Arkadi on 17 January 2020. An adult Red Kite is visible in the upper right corner. The other birds are Black Kites which comprise individuals with characteristics of both subspecies of migrans (Western Black Kite Milvus migrans migrans, see bright yellow legs) and lineatus (Black-eared Black Kite Milvus migrans lineatus, see pale/bluish legs) termed Eastern Black Kites likely originating from a hybrid zone in north-eastern Europe; b) A juvenile (2cy) Eastern Black Kite with migrans features (see brown underpart of wings without white window) and lineatus features (see pale/bluish cere and legs). Arkadi, 17 January 2020; c) A juvenile (2cy) Eastern Black Kite with lineatus features with a rufous dark head and pronounced dark eye-mask. Chersonesos landfill, 19 January 2020; d) A juvenile (2cy) hybrid Red Kite x Black Kite tagged with a telemetry logger (OT005). Arkadi, 20 January 2020; e) Left side: Black Kite not determined to subspecies-level, possibly an adult Western Black Kite (bright yellow legs and cere, rear underbody of the same colour as belly, rusty, according to Forsman (Citation2016) pp. 89, Fig. 99, underwing coloured more diffusely than in three-coloured pattern of lineatus). Right side: a juvenile (2cy) Eastern Black Kite with lineatus features (bluish cere and legs, three-coloured pattern of underwing with white window). Partheni landfill, 21 January 2020. f) Left side: a juvenile (2cy/3cy) Black Kite not determined to subspecies-level even though some lineatus characteristics are present (pale/yellowish legs and cere, the rear underbody lighter than belly). Right side: a juvenile (2cy) Eastern Black Kite with lineatus features (bluish cere and dark eye-mask). Arkadi, 20 January 2020. All photographs taken by P. Podzemný.
A total of 74 individuals were recorded from Facebook photographs comprising Black Kites (77%), Red Kites (20%), and Hybrids Black Kite × Red Kite (3%) (Table S1). There was an annual increase in the number of observations uploaded online from 2014 to 2019.
Our data suggest that there has been a significant increase in the number of wintering kites on Crete since 1998 (R2 = 0.307, df = 20, P < 0.01).
The tagged hybrid Red Kite × Black Kite OT005 ()) arrived on Crete on 3 October 2019 via Karpathos and Kasos and used a total of five roosting places during the winter period (). It roosted in numerous locations (roosting places; RP) throughout the winter months including RP1 (1 night), RP2 Partheni landfill (93 nights), RP3 Arkadi landfill (1 night), RP4 (23 nights) and RP5 Chersonesos landfill (39 nights). OT005 moved among RP2, RP4 and RP5 utilising these sites multiple times. On 6 March 2020, after a period of 157 days, OT005 died and visual examination of the carcass revealed electrocution by a medium-voltage electrical distribution powerline as the cause of death.
Figure 2. Movements of a hybrid Red Kite × Black Kite (OT005) during the wintering period on Crete. RP, roosting places (black circles), location of death (yellow triangle) and GPS locations of OT005 (blue circles) at 10 minute intervals. OT005 arrived from Kasos on 3 October 2019 and spent 157 days on Crete before its death on 6 March 2020.
Discussion
Our study is one of the first to document the wintering of kites in the genus Milvus on Crete. Previously, only seven Black Kites wintering on Crete were reported in 2009 using a driven transect sampling technique (Panuccio et al. Citation2019). We found large number of wintering kites on Crete which we believe to be a more recent phenomenon revealed by the annual increase in the number of direct and online observations especially since the winter of 2017/2018.
We considered whether the rise in the number of wintering kites may be tied to the increased activity of observers, equipment availability, popularisation of the internet and the increased uploading of observations online in recent years; however, it is unlikely that numerous numbers of wintering kites remained unnoticed during past decades. Furthermore, it has already been noted that the number of Black Kites wintering in the Mediterranean is increasing (Panuccio et al. Citation2013). The findings of Literák et al. (Citation2017) also suggest that the wintering of Black Kites in Greece has increased greatly since the turn of the century. Black Kites have also been wintering on Sicily since the early 1990s (Sarà Citation2003) and in Turkey since the early 2000s (Biricik & Karakaș Citation2011). However, these observations failed to identify individuals to subspecies-level and our supplementary approach of using online photographs allows us to identify birds to a finer taxonomic level and to identify Black Kites wintering on Crete with Milvus migrans lineatus morphological features (i.e. Eastern Black Kites).
We observed large flocks of wintering kites comprising both European kite species including a hybrid Red Kite × Black Kite. The highest congregations of kites were observed feeding from landfill sites which provide an abundant food source during the winter period for many raptor species (Pande et al. Citation2010; Arkumarev et al. Citation2014; Literák et al. Citation2017). Analysis of the satellite telemetry data also revealed a reliance on landfill sites throughout the winter period for OT005 until its death. Due to the scavenging nature of kites and high food availability (Panuccio et al. Citation2013), Crete can support high densities of kites during the winter months, acting as a winter refuge for individuals prior to the spring migration.
Our field and online surveys were not exhaustive and prior online content may have been removed, some suitable landfills also remained unchecked which could potentially impact the number of wintering kites included in our census. Despite this, our results filled a knowledge gap on the wintering of kites on Crete. Wintering kite populations should continue to be monitored and appropriate conservation action, including the safeguarding of powerline components by insulating dangerous wires and preventing the illegal shooting and poisoning of raptors, should be implemented to ensure population recruitment in succeeding years (Xirouchakis Citation2004).
Ethical approval
A telemetry study of Red Kites and Black Kites in Slovakia was permitted by The Ministry of Environment of the Slovak Republic (664/297/05-5.1pil, 2944/2017-6.3,4930/2016-2.3 and 8268/2020-6.3).
Geolocation information
Study area: Crete, Greece.
Supplemental Material
Download MS Word (28.7 KB)Acknowledgements
We would like to thank N. Tsiopelas and E. Hrtan, Jr. for providing important information on the studied kites and M. Skyrpan and two anonymous reviewers for providing valuable comments on the manuscript. We would also like to thank all photographers who uploaded photographs of kites online used in this study.
Disclosure statement
The authors declare no conflict of interest.
Supplementary material
Supplemental data for this article can be accessed here.
Additional information
Funding
References
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