Comparison of population densities of selected bird species breeding in main urban habitats in southwestern Poland

INTRODUCTION

Towns and cities may be successfully adapted as foraging and nesting grounds by a number of bird species (Witt et al., 2005). Avian communities in such habitats often undergo dramatic changes over a  relatively short period of time (Kalcey, Rheinwald, 2005). Those changes are often caused by a rapid decline of dominants or an increase in one or a few uncommon species. The underlying factor for such changes is human pressure, habitat destruction or alternation, food availability, or predation. Such factors are often country-specific and may be related to urban planning system, the level of economic development, social changes, politics, and management.

It may be interesting, therefore, to monitor the  species diversity and structure of breeding avian communities in typical urban habitats prone to such changes as block-building estates or residential areas. These habitats dominate in most cities and towns, but they are often interlaced with other habitats, such as parks, gardens and other timbered areas, industrial and rural areas, recreational areas, etc. They may influence both species composition and population densities of particular species.

In this study, a  city fragment comprising mainly a block-building estate and a residential area interlaced with a few minor habitats was selected to estimate population densities of less common breeding bird species and to compare the  densities between the  two habitats.

STUDY AREA

The study area is situated in the western part of Krzyki, a  district of the  city of Wrocław, SW Poland. The Ślężna Street was the eastern border of the  study area; a  railway marked the  western and south-western borders, and Krucza and Wielka streets the northern border (Fig. 1). The total surface of the whole study area was 384 ha. Four main urban habitats were distinguished in this area: (1) densely built-up areas (block buildings) – 130 ha, (2) areas with flat houses (residential area) with rich green areas (small gardens, hedge row, avenues, tree and shrub clumps) around – 149 ha, (3) timbered areas (parks, cemeteries, small timbered squares)  –  57  ha, and (4) ruderal areas and railway sides – 48 ha (calculation is based on Smolnicki and Szykasiuk, 2002).

Typically, block-buildings are 10–11-storied, but there are also some 3–4-storied buildings. These buildings are surrounded by numerous trees and shrubs, both indigenous and exotic (e.g., poplars Populus  spp., maples Acer  spp., oaks Quercus robur, birch Betula verrucosa, locust Robinia pseudoaccacia, horse chestnut Aesculum hippocastanum, willows Salix spp., spruces Picea spp., pines Pinus spp.), often with some mowed grass below and around these trees.

Some small timbered areas are composed almost entirely of deciduous trees, such as oaks, birches, poplars, maples, limes, locusts etc. They are interlaced with the build-up areas (Fig. 1).

METHODS

Counts were conducted in the  spring and early summer 2010 using a simplified version of the territory mapping method (Sutherland, 1996; Bibby, et  al. 2012), as in other urban studies on bird densities (Luniak et al., 2001; Otto and Witt, 2002; Kopij, 2005, 2007, 2012, 2014abc, 2016, 2017).

The study area was divided into eight parts. In each part, birds were counted by a  single researcher in one morning. The  survey of the  whole area was completed within one month. Four such complete surveys were therefore conducted, one survey in each of the following months: April, May, June, and July 2010. In total, 32 morning days were devoted to this study. During each count, all birds seen and/or heard were plotted on the map. Special attention was paid to singing males, birds showing breeding behaviour, and nests containing eggs or chicks.

The counts were conducted in the  morning between 6:00 and 11:00, in sunny or partly cloudy, windless weather. The  numbers of the Eurasian Magpie Pica pica, Hooded Crow Corvus cornix and Rook Corvus frugilegus were determined by counting their occupied nests.

Since the purpose of the study was to estimate population densities of most of the breeding non-passerine and less common passerine species, the  following species were excluded from the counts: Rock Dove Columba livia forma urbana, Common Swift Apus apus, House Martin Delichon urbica, House Sparrow Passer domesticus, Tree Sparrow Passer montanus, Common Starling Sturnus vulgaris, Great Tit Parus major, Blue Tit Parus caeruleus, European Greenfinch Carduelis chloris, and Western Jackdaw Corvus monedula.

RESULTS AND DISCUSSION

In total, 44 bird species were recorded as breeding in the  whole study area. For 34 of them, population densities were estimated and the distribution of their breeding pairs is presented on maps (Table 1, Figs. 2–27). Species which were excluded from the counts (see section ‘Methods’) were all classified as common breeding residents, each nesting in a  density higher than 10 pairs/100 ha.

Five species nested in a density higher than 10 pairs/100 ha each: Wood Pigeon Columba palumbus, Eurasian Magpie Pica pica, Collared Dove Streptopelia decaocto, Eurasian Blackcap Sylvia atricapilla and Common Blackbird Turdus merula (Table 1), and additional four species nested in a density of 5–9.9 pairs/100  ha: Fieldfare Turdus pilaris, Common Chaffinch Fringilla coelebs, Black Redstart Phoenicurus ochruros and Hooded Crow Corvus cornix (Table 1). A few other species were relatively common: Common Nightingale Luscinia megarhynchos, European Serine Serinus serinus, Common Redstart Phoenicurus phoenicurus, and Icterine Warbler Hippolais icterina (Table 1).

Table 1. Number of breeding pairs (N) and density (D: pairs/100 ha) in various urban habitats

Proportions between some congeneric species were calculated as follows: Turdus merula : T.  pilaris : T.  philomelos as 0.53  :  0.46  :  0.01 (n = 78 pairs of all three species); Sylvia atricapilla : S. curruca : S. communis as 0.87 : 0.11 : 0.02 (n  =  53); Phylloscopus collybita : P.  trochilus : P. sibilatrix as 0.88 : 0.07 : 0.07 (n = 16); Phoenicurus ochruros : P. phoenicurus as 0.76 : 0.24 (n = 37). The Common Blackbird was, therefore, already as common as Fieldfare Turdus pilaris, while the Eurasian Magpie was almost three times more common than the  Hooded Crow.

Whereas in the  densely built-up areas the  Wood Pigeon and Collared Dove were equally common, the Collared Dove was almost three times more common than the Wood Pigeon in the residential area (Table 1). The Eurasian Magpie was about three times more common than the Hooded Crow in both the built-up and residential areas. Similarly, the House Redstart was about three times more common than the Common Redstart in both of these habitats.

Only one species, the  Eurasian Magpie, reached the density of over 10 breeding pairs/100 ha in all four habitats surveyed (Table 1). The Common Blackcap nested in such density in all habitats, except for the densely built-up areas. The Wood Pigeon and the Collared Dove reached such density in two habitats, while the Common Blackbird nested in such density only in parks (Table 1).

No Dunnock Prunella modularis or Wren Troglodytes troglodytes were observed, and only a  single pair of the  Song Thrush Turdus philomelos was recorded as nesting in the study area (Table 1). In Western Europe, they are very common breeders in urban habitats (Witt et al., 2005; Fuller et al., 2009). On the other hand, the House Sparrow, Tree Sparrow, Common Starling, Western Jackdaw, Fieldfare, Lesser Whitethroat Sylvia curruca, Icterine Warbler, and Serine are much common in Wrocław and other Polish cities than in German or British ones (Kalcey, Rheinwald, 2005; Witt et al., 2005; Fuller et al., 2009; Kopij, 2012, 2014abc, 2017).

This study suggests that although densely built-up and residential areas have a  similar species composition, many species breed in different densities. This is probably due to the different structure of vegetation. While tall trees are relatively common and shrubs are rare in densely built-up areas, the  reverse situation prevails in residential areas.

References

Grzegorz Kopij

PAUKŠČIŲ RŪŠIŲ, GYVENANČIŲ PAGRINDINĖSE MIESTO BUVEINĖSE PIETVAKARIŲ LENKIJOJE, POPULIACIJOS TANKIO PALYGINIMAS