Introduction

Although the barn swallow (Hirundo rustica Linnaeus, 1758) occurs at all altitudes in Slovakia (Matoušek & Országhová 1994), its breeding biology has not been given adequate attention. In the former Czechoslovakia, Kondělka (1985) studied clutch size and breeding success in northern Moravia in 1967 – 1979. Pikula & Beklová (1987) report nest dimensions and number of eggs per clutch, length of incubation and egg dimensions from the former Czechoslovakia. In 1963 – 1964, Kuźniak (1967) observed the arrival, nest building, clutch size, feeding of the young and autumn departure of Barn Swallows, in the surroundings of Poznań (Poland). In Denmark, Møller (1982) reported a positive correlation between nest size and clutch size. In Austria, Fally (1989) studied the relationship between breeding success and nest size, nest orientation and location. He observed that clutches in nests located in stables were smaller on average than those in cooler spaces e.g. of store­rooms. Møller (1984) found that the mean size of the first clutch does not depend on the geographical situation of the nesting locality.

The present study deals with length of nesting, clutch size, egg dimensions and breeding success of the Barn Swallow in southwestern Slovakia.

Area of Study and Methods

The study was carried out in 1993 – 1995 on the right bank of the Danube in the south–western part of Bratislava – Rusovce (48°3´ N, 17°10´ E) and Bratislava – Ovsište (48°8´ N, 17°7´ E) in eight stables. Six of these housed cattle. Four of the stables were of the classical type with tiled roofs; two were more modern with a gable roof with glass panes (Bratislava – Rusovce). The stable doors on both side s were kept open most of the year, with air circulating inside all the time. The cattle were stabled all the year round. Two of the stables were for race horses (Bratislava – Ovsište). The smaller one was a brick building, the other, a modern one, was roomy, built of concrete precast units.

All the nests were controlled twice a week. Eggs were weighed using Pesola field scale, to an accuracy of 0.5 g and measured with a slide gauge, with an accuracy of 0.02 mm.

Results

First Eggs and Clutch Size

The study comprised a total 107 nests. Clutches were initiated between 29 April and 10 August (Fig. 1). Hence, the total period during which clutches were started lasted a total of 104 days. The largest number of clutches (7) were initiated on 12 May.

First clutches were started during a period of 58 days (from 29 April to 25 June) and second clutches during 71 days (from 31 May until 9 August). The first eggs in two third clutches were laid on 13 July and 10 August (Fig 1).

A total of 153 nestings took place in 107 nests; the swallows were observed to nest twice in 45 nests, once only in 57 and three times in 2 nests. Nine clutches failed – 5 were abandoned – (three clutches of 6, 5 and 3 eggs, respectively, three clutches of 4 eggs each, two clutches of 1 egg each, one case in which all 4 nestlings of a 4–egg clutch perished). No more than 5 replacement clutches were found in all of the controlled nests.

A total of 739 eggs were laid in 162 clutches, giving a mean of 4.5 eggs per clutch (x = 4.56 ± 0.90; SO = 1.14, n = 162). First clutches nesting had a mean of 4.9 eggs ± 0.94; SO = 0.10, n = 88, second clutches a mean of 4.1 eggs ± 0.14; SO = 1.23, n = 72).

Of the 162 clutches, 77 or 47.53 % had 5 eggs. Among first clutches (n = 88), the corresponding proportion was 57 %. In second clutches 51 out of 72 (45.8 %) had 4 eggs (Table 1).

In four of the nests (three first clutches and one second clutch) we found clutches of 7 eggs. In the case of the 9–egg clutch (Table 1), it cannot be ruled out that the eggs came from two females.

Weight and Dimensions of Eggs

Mean egg weight was 2.0 g (x = 2.09 ± 0.01; SO = 0.23; n = 665), the lightest egg weighing 1.2 g and the heaviest 3.0 g. The latter came from a clutch of 4 eggs. By far the greatest number of eggs (210) weighed 1.88 – 2.00 g (Fig. 2).

The mean length of the eggs was 19.5 mm (x = 19.55 ± 0.037; SO = 0.95; n = 665) – the shortest measuring 14.6 mm and the longest 22.4 mm. Most eggs (103) tell in the range 19.75 – 20.00 mm (Fig. 3).

Mean egg width was 13 mm (x = 13.86 ± 0.022; sx= 0.56; n= 665) – the narrowest one measuring 12.4 mm and the broadest one 19.0 mm. Most of the eggs (193) had a width between 13.75 and 14.00 mm (Fig. 4).

Breeding Success

Of the total of 739 eggs, 25 (i.e. 3.38 %) were destroyed (thrown out of the nest, or the whole nest fallen). Of the 714 remaining eggs 167 (22.60 %) failed to hatch. These were either unfertilized or contained dead embryos. Thus from the 739 eggs laid, 547 young hatched (i.e. 74.02 %). Nestling mortality between hatching and nest leaving was 5.12 %. A total of 28 fledglings perished either because they fell out of the nest, or because of to the skin on the sides of the neck down to the shoulder caused by the sharp claws of nest mates. These nestlings probably perished from secondary infection (3 cases). In the two third clutches, all six young that hatched also fledged. The fledging success was 94.52 %. The breeding success was 69.96 %.

In first broods 4.26 % of the nestlings died while nestling mortality in second broods was 6.6 % (Tab. 2). In first clutches hatched 76.33 % of eggs, in second clutches only 70.90 %.

Of the 14 young that died in first broods, five came from clutches of 5 eggs; in three clutches of 6 eggs, 1, 2 and 4 nestlings died, respectively. The remaining two young that perished came from clutches of 3 eggs. In second brood 14 nestlings died. Two of them were from clutches of 3, eight from clutches of 4 and three from clutches of 5 eggs.

Incubation Period and Duration of Nesting

The incubation period ranged from 12 to 18 days, with a mean of 14.83 days (n = 103). The difference in incubation between the first and second nesting is minimal (14.92 in the former and 14.71 in the latter). The minimum incubation period of 12 days was observed four times and the maximum (18 days) only once (Tab. 3). In this case the clutch counted 7 eggs out of which 5 young hatched.

The mean number of days from nest leaving to the start of egg laying in the next nesting was 9.5 days. In one case was the first egg of second clutch laid before the first brood young had left the nest.

The mean length of nestling feeding was 21 days (x = 20.88 ± 0.20, n = 136), the minimum being 14 and the maximum 26 days (Tab. 4). The difference in the duration of nest feeding between the first (20.75 days) and the second nesting (21.09 days) was not statistically significant (t = 0.78, P = 0.22).

The mean total nesting time (from laying of the first egg to nest leaving) was 90 days in two nestings and 41 days in one nesting. The minimum time with two nestings was 82 and the maximum 100 days. With one nesting, the minimum length was 31 and the maximum 74 days.

Figure 1. Dates of first egg laying.

Figure 2. Distribution of barn swallow egg weights.

Figure 3. Distribution of barn swallow egg lenghts.

Figure 4. Distribution of barn swallow egg breadths.

Table 1. The distribution of clutch sizes in first, second and third clutches of barn swallows near Bratislava.

Table 2. Breeding success of barn swallows near Bratislava.

Table 3. The length of the incubation period in first, second and third clutches of barn swallows near Bratislava.

Table 4. The length of the nestling period in first, see third broods of barn swallows near Bratislava.

Discussion

The period during which Barn Swallows initiated clutches in the surroundings of Bratislava lasted 104 days – from 29 April to 10 August, which is in accordance with other studies. From the surroundings of Poznań in Poland, Kuźniak (1967) found this period to be from 1 May to 9 August, hence 101 days. In northern France, the corresponding period lasted from 28 April until 9 August, hence 102 days (Jarry 1982).

The mean number of eggs per clutch in the surroundings of Bratislava was 4.56. Similarly, Pikula & Beklová (1987) reported a mean of 4.47 for clutches from the whole of Czechoslovakia. Kondělka (1985) mentions 4.53 eggs for the surroundings of Ostrava. He found five clutches of 7 eggs each and one clutch of 8 eggs. In Austria (Burgenland), the mean number of eggs per nest inside a building was 4.9 (Fally 1989) and in the surroundings of Poznań it was 4.4 (Kuźniak 1967). Kuźniak (1967) found a 7–eggs clutch in only one case. Similarly in France, the mean number of eggs per clutch was 4.4 (Hemery et al. 1979). In large swallow colonies (8 – 22 pairs) the number of eggs per clutch was lower (4.6 in first and 4.2 in second clutches) than in solitary nests, where the average was 5.8 in first and 4.3 in the second clutches (Shield & Crook 1987). Brood size is influenced by seasonal factors and also by the presence of parasites. Ectoparasitism can by one of the factors that explain small broods of birds (Møller 1990, 1994, Poiani 1993). The numbers of mites can reach up to thousands and can negatively influence the hatching successfulness (Heeb et al. 1998; Krumpál et al. 1995; Krumpál et al. 2001; Mašán & Országhová 1995; Møller 1990; Richner & Heeb 1995).

The mean weight of swallow egg from the surroundings of Bratislava of 2.09 g slightly exceeds the values reported by some authors from neighbouring countries, e.g. Balát (1983) 1.99 g, Pikula & Beklová (1987) 1.88 g, Kuźniak (1967) 1.86 g. Matoušek (1956) gives a mean weight of 2.18 g for eggs from western Slovakia.

The mean values of dimensions (length x width), 19.55 x 13.86 mm, for eggs from the surroundings of Bratislava are slightly higher than those reported by Balát (1983) – 19.39 x 13.67 mm and Pikula & Beklová (1987) – 19.29 x 13.65 mm. Matoušek (1956) gives the dimension of 20.08 x 13.64 mm from western Slovakia, while Goebel (in Dementev et al. 1954) reports 18.0­ – 20.5 x 13.0 – 14.0 mm from Ukraine.

In the present study the mean number of fledglings was 4.83. Kondělka (1985) gives a mean of 4.07 fledglings.

Pikula & Beklová (1987) state that the incubation period ranges from 13 to 20 days, which a mean of 15.1 days, while Kuźniak (1967) found it to be 12 – 18 days, with a mean of 14 – 15 days. Møller (1991) also reports it to last. 15 days. In south–western Slovakia it was likewise within the range of 12 – 18 days, with a mean of 14.8 days (present study).

Nestling mortality from hatching to nest leaving in the surroundings of Bratislava amounted to 5.12 %. Balát (1983) reports an even lower rate (2.65 %).

Acknowledgements

The author wishes to express her appreciation to Prof. Ladislav Jedlička (Bratislava) for their valuable comments on her manuscript. This study was supported by the Slovak Grant Agency KEGA grant No. 007 UKF–4/2012.

References