EVALUATION OF PREDATOR’S PRESSURE ON HATCH OF RING-NECKED PHEASANTS PHASIANUS COLCHICUS IN URBAN AND AGRICULTURAL AREAS BY MEANS OF ARTIFICIAL NESTS

Piotr Czyżowski, Mirosław Karpiński, Leszek Drozd
Department of Pet Breeding and Wildlife Management, University of Lifes Science in Lublin, Poland

ABSTRACT

Studies consisted in the evaluation of predator's pressure on hatch of Ring-necked pheasant Phasianus colchicus living in cities and agricultural areas by means of laying artificial nests (camouflaged and open). The stronger predator's pressure on pheasant's hatches in urban than agricultural areas was found. Higher pheasant population density in cities as compared to neighboring agrocenoses at stronger predator's pressure on pheasant's hatches in city area suggests that other environmental factors have higher influence on pheasant population than predator's pressure. Corvids Cervidae, namely European magpies Pica pica in cities, while Red fox Vulpes vulpes then Corvids in rural areas are the main damage perpetrators among pheasant's hatches. In cities, predators damaged first of all nests on open area, while in agricultural area, their penetration focuses mainly the middle-field trees.

Key words: pheasant, predator’s pressure, artificial nests.

INTRODUCTION

The increase of some wild animal species population, including those whose agricultural environment had been their up-to-date biotope, has been recently observed in cities and suburban areas. Still growing cities occupying habitats of wild animals make that numerous species chose areas within administration limits of cities as their living environment. A great diversity of city environment that compensates them for anthropopression is one of the reasons of their population increase [20]. At the same time, the agricultural areas adjacent to those cities have been also transformed. The changes mainly consist in forming the large-area monocultures and decrease of the field biotopes diversity, which in consequence affected the decrease of the field game population in agrocenoses [17,18]. Learning the population parameters of species living in cities and adjacent agricultural areas may be useful in explaining the reasons of the field game population decrease recently observed.

The present study aimed at comparing the predator's pressure on hatch of pheasants colonizing cities and adjacent agricultural areas.

MATERIAL AND METHODS

Studies carried out since April till May 2008 consisted in the evaluation of predator's pressure on hatch of pheasants living in cities and agricultural areas on a base of a methodology applied in earlier research [2], by means of laying artificial nests imitating the natural hatching. Therefore, 40 artificial nests (14 in cities and 26 in suburban areas) including 5 hen's not-incubated medium brown eggs were laid at the beginning of April. In particular nest, eggs were placed in a small cavity with no special camouflage (open nests). Each nest was marked with a numbered badge. All nests were laid on areas where the local pheasant population occurred. The largest number of nests were placed in allotment gardens (6 nests), then city park (4 nests), and wastelands (4 nests). Within agricultural areas, 10 nests were put in middle-field trees, 5 at the border between fields and forests, 6 on meadows, and 5 on open fields.

The site of nest laying was randomly selected; however, such items as trees, balk, etc. prevailed. The surface area of particular study sites was about 500ha with mean distance between artificial nests about 400 meters.

In order to evaluate the predator's pressure on laid nests, 4 inspections with one week intervals were made. The first inspection was performed a week after hen's egg laying (first week of April). During the inspection, the number of eggs remained in nests and the damage symptoms indicating the perpetrator (tracks, ways of the eggshell damage, droppings remained) were recorded. The percentage of damage perpetrators in relation to all laid eggs was calculated. The extent of predator's pressure on pheasant's hatches in city and agricultural areas was evaluated on a base of the damages among laid eggs. The damage magnitude was defined as a percentage in relation to all laid eggs on a given area. The trend lines along with regression equations were determined to compare the damage tendencies among open nests in subsequent controls in city vs. agricultural area. Such trend lines and regression equations were also determined for damage size among masked and open nests.

To evaluate differences in predator's pressure on compared areas, the significance test for differences between fractions was applied [13].
The city area comprised of the administration limits of Lublin and included the allotment gardens, city park and slum areas localized in its eastern part. The agricultural area was consisted of grounds of villages: Strzeszkowice and Radawczyk Kolonia localized within Niedrzwica Duża commune that is adjacent to Lublin administration limits (14 nests) as well as areas of Uściąż village in northern part of Karczmiska commune (12 nests) in Lublin region. Niedrzwica Duża commune is a typically agricultural with about 85% agricultural lands, while Karczmiska commune is a village with 72% agricultural lands.

Taking into account the fact that pheasant's females leave the nest very rarely, when hatching eggs, the study methodology was modified [4]. Therefore 12 additional nests (with 5 eggs each) completely covered with straw to camouflage them, were laid in Karczmiska commune.Most of masked nests were put in middle-field bushes (5 nests), 4 nests were placed at field-forest border, and remaining 3 ones on open fields.

Then, the nests were inspected with week intervals, the same as in the case of open ones, and the size of damage and the percentage of damage perpetrators was evaluated. To evaluate differences in predator's pressure on open and covered nests, the significance test for differences between fractions was applied.

In addition, a stocktaking of pheasants on compared areas was performed, which consisted in everyday listening to tooting male pheasants in the morning, i.e. their highest activity time, since mid of April till mid of May 2008. Particular listening of a single individual lasted about 20 minutes. When larger number of males tooted at the same time, the duration of the listening was prolonged to estimate the number of individual birds more detailed. Females accompanying the males were also counted during the stocktaking. A spring population of pheasants (n/100ha) was calculated using a formula: Y=(0.9X–0.8) x (1+Z), where: X – average number of male pheasants recorded in sites, Z – number of female pheasants corresponded to a single male pheasant [14].

RESULTS

The spring pheasant inspection revealed higher bird's population in cities than in agricultural areas. In cities, mean pheasant population density was 8.1 n/100ha, while in suburbia 3.0 n/100ha (4.2 n/100ha – Niedrzwica Duża, 1.8 n/100ha – Karczmiska). Pheasants live in almost all green places within Lublin city boundaries: parks, allotment gardens, river Bystrzyca valley meadows, and all agricultural and degraded areas. The tooting pheasants can be met even on lawns and house gardens localized in a strict city center in spring. The ratio of pheasant sexes (males to females) within Lublin city was 1:1.5, although a single male led one or two females.

Higher predator's pressure on pheasant hatches was observed in city as compared with agricultural areas. The damage extent among artificial nests in Lublin was 75.7%, whereas the average size of damages in agricultural areas made up 56.9% among all laid eggs. The difference was statistically significant for the significance level of p = 0.05. Value of test function calculated using the significant test for the difference between fractions z₀ was 2.63 at critical value z_0.05=1.96. The percentage of damages in reference to all damaged eggs on compared areas during particular inspections is different. Most of damages among artificial nests was found in the first week of study (Fig. 1). Higher damage rate among artificial nests within agricultural area as compared to the city is illustrated by plotted trend lines. The agricultural area was characterized by higher egg damage rate with over 60% of total damages during the first inspection.

In the city, the largest number of damaged nests was localized within allotment gardens and city park (Fig. 2), while in agricultural area, the most of damages referred to nests localized in middle-field bushes and the boundaries between fields and forests (Fig. 3). Study also revealed the differences in the damage perpetrators of laid eggs on compared areas (Fig. 4). In the city, over 60% of all damages were made by Corvids Corvidae , mainly European magpies Pica pica, which was proved by the way of eggshells damage (wholes) and the presence of numerous population of that bird on studied area. Other perpetrators were responsible for remaining damages: Red fox Vulpes vulpes (tracks and fox odor), Beech marten Martes foina (droppings and tracks), Common hedgehog Erinaceus europaeus (observed a single individual near the nest), and humans (grass mowing). On agricultural areas, the main perpetrator appeared to be Red fox (tracks, presence of fox holes), then predators of Corvids family: European magpie and Eurasian jay Garrulus glandarius (pecked out eggshells and the birds presence near damaged nests).

Comparison of the damage extents between open and masked nests revealed about 65% and 45% damages (open and camouflaged nests, respectively) made by predators. The difference was statistically significant at the significance level of p = 0.05. Value of the test function calculated by means of significance test for the difference between fractions z₀ was 2.15 at critical value z_0.05=1.96. Also the egg damage rate was higher in the case of open as compared to masked nests. More damages among open than covered nests were observed just in the first study week (Fig. 5). The rate of egg damage was also higher in the case of open nests comparing to masked ones, which is illustrated by trend lines.

The nest localization was very important in the experiment involving the nest camouflage (Fig. 6). The largest number of damages in masked nests occurred around the field-forest border. On a forest area, the percentage of damage among covered and open eggs was similar, while on open fields, predators damaged only open nests.

DISCUSSION

The predator's pressure on bird's hatch expressed as the number of damaged eggs may be an indicator of the predator's pressure on the whole population [12]. Some scientists [9,15] report that the population density of predators damaging the hatches is the main factor that regulates the gamefowl population increase. Here performed studies confirmed higher pressure of predators on pheasant hatches in the city area found in earlier examinations [3]. Gering and Blair [6] also reported higher predator's pressure on bird's hatch on urbanized areas, but in their opinion, the predator's pressure decreases along with the increase of urban environment urbanization level. According to others [10], the pressure in city areas differs in particular countries. As their studies revealed, in Finland, predator's pressure in city area was higher than in surrounding forests, and in countryside. In Italy, no differentiation of predator's pressure between urban, rural, and forest areas was recorded, while in Spain, the pressure in suburbia was higher than in cities. According to above studies [11], corvids were the main perpetrators of damages in city area in Finland, while other predators, namely dogs and cats, in Italy and Spain.

The predator's pressure is one of the main reasons for pheasant's mortality. Fox is considered as its main predator. Although pheasants are not their main food, studies made by Robertson & Whelan [16] revealed that about 70% of pheasant's mortality might be due to foxes. In present study, fox was the main predator in agricultural areas. Corvids damaged nests laid on more populated areas and localized nearer city centers (city park, allotment gardens). The increase of corvids population in cities, mainly magpie Pica pica [8] caused that they are the main predators that damages bird's hatches in cities [5]. In Lublin, The most numerous damages were found among nests laid in the city park, which was associated with the presence of numerous magpie population. On agricultural area, the largest number of damages referred to nests laid among middle-field trees that, according to Goszczyński [7], are firstly inspected by predators. Other authors' studies [19] revealed that predators exert stronger pressure on nests localized among the middle-field trees. In their opinion, nests laid on a ground are damaged mainly by predator mammals. Angelstam [1] found that predatory mammals were the main damage perpetrators among nests laid on cultivated fields as compared to forests, where nests were mainly damaged by bird predators.

It seems interesting to compare damages among covered and open nests. On open fields and middle-field bushes, predators damaged first of all not camouflaged nests, while no damage was found among masked nests. It was also confirmed by other authors' studies [1], in which the percentage of the eggs' damage increased along with the increase of their visibility.

CONCLUSIONS

The stronger predator's pressure on pheasant's hatches in urban than agricultural areas was found. Higher pheasant population density in cities as compared to neighboring agrocenoses at stronger predator's pressure on pheasant's hatches in city area suggests that other environmental factors have higher influence on pheasant population than predator's pressure.

Corvids Cervidae, namely European magpies Pica pica in cities, while Red fox Vulpes vulpes then Corvids in rural areas are the main damage perpetrators among pheasant's hatches. In cities, predators damaged first of all nests on open area, while in agricultural area, their penetration focuses mainly the middle-field trees.

In studies upon the predator's pressure on pheasant hatch using artificial nests, application of the complete nest camouflage seems to be more exact, because that methodology imitates natural conditions more accurately.

REFERENCES

Accepted for print: 3.11.2009

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