The breeding distribution and numbers of the Jackdaw (Corvus monedula) in Kharkiv City, Ukraine

counts of breeding Jackdaws were made in Kharkiv City,


Introduction
The Jackdaw (Corvus monedula) is a common and widely distributed species in Kharkiv City, Ukraine. More than 120 years ago in Kharkiv region the Jackdaws nested in niches, holes, crevices of buildings especially under roofs, in attics, in brick chimneys, church towers (Somov, 1897) as they do today. The tree-hole nesting (in hollow trees) was quite common at the end of 19 th century but is not recorded in Kharkiv City and neighboring areas nowadays though more than 50 years ago the Jackdaws formed colonies and nested in tree cavities in oak forest at approximately 90 km from Kharkiv City (Novikov et al., 1963). Also the Jackdaws nested in niches and holes in loessial and more rarely granite slopes (holes in cliffs) in some parts of Mykolayiv, Vinnytsya and Zhytomyr regions of Ukraine until 1990 (Loparev, Yanish, 2010).
The Jackdaw was once assigned to a group of species with high tolerance to climate change based on the results of the analysis of life history traits e.g. trophic niche, number of brood attempts per year, life expectancy and others (Banik, Atemasov, 2010) thus presuming that the species may be at least less vulnerable to climatic fluctuations. The population trends for the Jackdaw in some European countries e.g. in the Czech Republic, Hungary, Slovenia are declining but are stable or even increasing in the others as in Finland, Sweden, the United Kingdom, Belgium (Božič, 2016;Wild Bird Populations..., 2018). Moreover, the population trends can be different among regions and habitats. Thus, for example, the increase in farmland and the decrease in woodland habitats were observed in the United Kingdom (Common Birds Census 1964-1993Gregory, Marchant, 1996). In Ukraine the woodland population tends to decrease during last 35 years (Senik, Gorban, 2015) and nesting in steep holes is not noticed anymore (Loparev, Yanish, 2010). The oppositely directed population trends are evident in different regions of Ukraine. Thus, the numbers of breeding Jackdaws decreased at the begining of 21 st century in Western Ukraine (Horban, 2002;Senik, Gorban, 2015;Bokotey et al., 2010), but apparently increased in

Method
The counts of the numbers of Jackdaws were carried out in Kharkiv City, Ukraine, in 2016-2017 with the main purpose to estimate the breeding density, Kharkiv population size and the distribution across different habitat types. The city area was divided into 0.25 km² squares (n = 1354). QGIS program was used to choose randomly 40 squares where the numbers of nesting birds were then counted and mapped ( Fig. 1). We could not accommodate stratified sampling scheme because it required more counts efforts within industrial areas where in most cases special permissions are needed to work. The surveys were made in April-May (19 squares) and early June (4 squares) in 2016 and April-May (10 squares) and early June (7 squares) in 2017. Thus the time span of the surveys (April to early June) coincided with the Jackdaw breeding period (see also Cramp, Perrins, 1994;Podobivskyi, Kotiv, 2016). We accomplished a distribution study with use of single species count method (Bibby et al., 1993;Czechowski et al., 2013).

Fig. 1. The distribution of squares surveyed in Kharkiv City
The breeding distribution and numbers of the Jackdaw (Corvus monedula) in Kharkiv City, Ukraine

Вісник Харківського національного університету імені В. Н. Каразіна
The Journal of V. N. Karazin Kharkiv National University Then we determined the numbers of nesting birds by extrapolating the collected data for the main habitat types e.g. area of residential blocks of flats, residential area (1-2-storey buildings), industrial area, forest zone, park zone and undeveloped urban areas. The data on the area occupied by every major habitat type (in km²) were calculated by QGIS program. Thus 90 % of the territory of Kharkiv City was analysed, except water reservoirs and traffic way areas. This calculation was confirmed with the vector data gathered at the beginning of 2000's. Moreover, we conducted an additional survey in search of all Jackdaw colonies within the boundaries of Kharkiv City in 2016-2017 to take into account the most numerous colonies. The data of 2016 year survey were used in European Breeding Bird Atlas 2 (EBBA2) programme (square 37UCR2).
Descriptive statistics were used in the analysis of the data on the breeding density of Jackdaw (Gould et al., 2020). Confidence intervals were calculated with application of bootstrap procedure (100 000 resamples) with use of Statistics101 vers. 5.2. (Grosberg, 2020).

Results: breeding density and population size
The data on the breeding density of Jackdaws are summarized in Table 1. The species prefers to nest at suitable cavities such as wall holes, crevices, chimneys, ruined buildings and ventilation system in old 3-5-level buildings at built-up districts or in round cross-sections of posts and poles at residential blocks of flats areas where the mean density was 22 pairs/km². In industrial areas the mean density of Jackdaw was 15 pairs/km². At undeveloped urban areas several pairs can use adjacent poles for nesting.  The total size of the breeding population of Jackdaw within the borders of Kharkiv City was estimated based on the calculated areas of major habitat types. The total number of breeding Jackdaws was estimated at 2325 pairs (see Table 2 for the details).
The Jackdaws form not only loose settlements with the maximum number of 16 pairs per square (Table 1) but more numerous and dense colonies in Kharkiv City (Table 3). One colony which comprises 150-160 pairs is located in old buildings of Kharkiv Tile Plant and another one is situated at main building of V.N. Karazin Kharkiv National University in city centre. Taking into account these data, the overall estimate for the size of breeding population of Jackdaw in Kharkiv City may be corrected to 2630 pairs.

Discussion: population size and suitable habitats
Our data suggest that the numbers of breeding population of Jackdaw within the borders of Kharkiv City (roughly an area of 350 km²) are about 2325-2630 pairs. Unfortunately, a few published data on other Ukrainian cities exist. But, for comparison, only 176 pairs of Jackdaws nest in Khmelnytsky city with an area of 86.2 km² (Iljinsky, 2009). In Khmelnytsky almost all colonies are located at built-up districts with old 4-5-level buildings with mean density of 26.5 pairs/km² (Iljinsky, 2009). The similar mean density of 22 pairs/km² is observed in present study for Kharkiv's residential blocks of flats areas. In some residential quarters of Lviv City the general breeding density of Jackdaw are 18.8 pairs/km² (Senik, Kasparova, 2012).
This study shows that the Jackdaw uses only urban habitats in Kharkiv City. Generally in Ukraine, the Jackdaw typically nests in urban areas (Nadtochiy, Ziomenko, 2001;Bashta, 2003). Indeed the most important factor for Jackdaws' survival is an availability of suitable nest cavities (Salvati, 2002;Bochenski, Czechowski, 2005;Iljinsky, 2009), thus renovation of old buildings with an aim of thermal insulation can lead to the decline in numbers or even to local extinction (Czechowski et al., 2013;Božič, 2016). For example, in Khmelnytsky city (Ukraine) the Jackdaws nest only in building's niches and crevices and prefer the old ones (Iljinsky, 2009(Iljinsky, , 2012. Our findings highlight the fact that the Jackdaws in Kharkiv City are most numerous at built-up districts and industrial areas where they have an opportunity to nest in cavities of old buildings. It may be supposed that the reconstruction of old and relatively newish buildings during the last decade will have an adverse effect on the Jackdaws because they have to face with a lack of suitable nest sites. The Jackdaws also can nest in hollow round cross-sections of posts and poles in Kharkiv City as well as in other Ukrainian regions (Nadtochiy, Ziomenko, 2001;Loparev, Yanish, 2010;Senik, Gorban, 2015). All the above mentioned certainly doesn't mean that the Jackdaw is indeed a well-urban-adapted species in Europe. One recent study has demonstrated that a lack of high-quality food especially during breeding period may limit breeding success in this species (Meyrier et al., 2017). The decreases in population of the Jackdaw can be attributed to a decrease in a food supply (Tiainen, 1985). Thus, the distance between breeding and foraging sites plays an important role for the Jackdaw survival (Bochenski, Czechowski, 2005;Iljinsky, 2009). In Kharkiv City the species is not only practising the searches for people's leftovers from dustbins but also prefers to forage in flood-plain areas, in park zone, and on agricultural fields situated nearby to the city boundaries. Namely, the largest colonies of western parts of Kharkiv City are found in close proximity to the suitable foraging sites. The two biggest colonies of the Jackdaws in Kharkiv City (the first and the second in Table 3) are associated and located near the rookeries. These two species, the Rook and the Jackdaw, are very similar in their feeding habitat preferences in breeding time (Yanish, 2012). Individuals of both species participate in formation of mixed flocks including foraging groups and communal roosts (Bresgunova, 2009). In other parts of Ukraine such as Vinnytsya Region, south of Zhytomyr region and south-west of Kyiv Region, and Lviv City (Western Ukraine) the Rooks and Jackdaws often nest together (Loparev, Yanish, 2010;Senik, Kasparova, 2012). Moreover, the Rooks seem to appear and build their nests in such colonies early than Jackdaws (Senik, Gorban, 2015). Such a habit when the both species tend to nest together has been observed also in other European and Asian countries (Gavrin, 1974;Cramp, Perrins, 1994;Repin, 2012).
We recommend the use of our survey scheme to monitor the state of the breeding population of Jackdaw in Kharkiv City in the future and especially to track the trends in different habitat types.