Study subjects

a) The studied house sparrow population

We have been studying the house sparrow population since 2004 in and around the territory of the Zoo of Veszprém, in Veszprém (47º05′ N, 17º54′ E), north-western Hungary, where sparrows are resident all year-round. They breed in high numbers (>50 pairs) in the zoo, using both nest boxes and natural nesting sites, and for the whole zoo area the population size is estimated several hundreds in each autumn when young birds are present in large numbers (Bókony et al. 2008). For our study purposes, non-breeding adults were captured with mist-nets and were ringed at regular intervals (1 or 2 days weekly) during autumn and early winter (September – December) in each year, with some additional ringing of breeding adults during spring and summer. Breeding birds were also occasionally caught using a nest-trap fitted on nest boxes during the nestling feeding period. In addition to adults, we ringed 9-11 days old nestlings both in nest boxes and at natural nest sites in the zoo throughout the years. All birds (including nestlings) were ringed with a numbered metal ring and three colour rings for individual identification. We also took a small amount of blood from each bird from the brachial vein and stored it in Queen’s lysis buffer (Dawson et al. 1998) until genetic analysis (see below).

b) Free-living wintering flocks

For the analyses of kinship structure (Study 1), fieldwork was conducted in 2004 – 2006, which included ringing and blood-sampling of free-ranging sparrows and their subsequent observations at five study sites to collect data on group composition and associations between individuals. Four of our five study sites were situated in and around the Zoo of Veszprém (northern site, N; western site, W; central site, C; and southern site, S),

whereas one additional site was on the nearby campus of the University of Pannonia (U), south-east from the zoo (Fig. III.1).

Figure III.1. Map of the study area. Study sites are indicated by the centre of the circles, and the diameter of the circles is proportional to core-flock size (number of ringed house sparrows observed exclusively at that site) in 2006. Lines connecting the circles indicate the movements of commuter birds (i.e. those moving between sites), line width is proportional to the number of commuters between the respective sites in 2006.

Each site had a group of shrubs where the sparrows regularly roosted during the day, and some adjacent open area where they could feed (see below). Distances between sites ranged between 229 – 1225 m (mean  SE = 669  111 m), and they were separated from each other by forest tracks (typically mature Austrian pine Pinus nigra) or built-up areas (Fig.

III.1). In 2004 regular ringing was restricted to two zoo sites (W and C), whereas in 2005 all sites were involved. In 2006, we estimated the maximum number of birds present during the observations at each site, and median of these flock sizes were 21, 32, 100, 65, and 12 individuals for site N, W, C, S and U, respectively. In total, 410 house sparrows were ringed and blood-sampled before the start of the 2005 observation period, whereas the cumulative number of ringed individuals was 1244 by the start of the 2006 observation period (not all observed subsequently, see below).

c) Captive house sparrow flocks

The effect of relatedness on different aspects of social behaviour (Studies 2-5) was investigated on captive birds. We captured house sparrows with mist nets during autumn in 2005–2006 within the territory of the Zoo of Veszprém. Because we had monitored the breeding of ringed birds and had also ringed the nestlings (see above), we had pedigree information for many individuals by the time of capture. We allocated the captured birds into two flocks in 2005 and formed one flock in 2006, so that each contained same-brood siblings (Table III.1).

Table III.1. Characteristics of the captive house sparrow flocks.

Flock 1 Flock 2 Flock 3 Number of same-brood siblings 9

(3 dyads, 1

Conducted studies Study 2-5 Study 2-5 Study 3-5

Number of scroungings (i.e. individuals). Sex ratio of the flocks (Table III.1) was similar to those of free-living foraging flocks at our study site (41–63%, calculated from ringing data; see also Bókony et al. 2008) and those reported by Breitwisch & Hudak (1989). Adults were caught either in September after cessation of reproduction or, in a few cases, in June–July together with their offspring (and were held together in outdoor aviaries), so dependent youngs’ lives were not risked by our work. Upon capture we measured body mass (± 0.1 g), tarsus length (± 0.1 mm) and took small blood samples (approximately 100 μl) for kinship analyses. Each individual was ringed with a numbered metal ring and three colour rings. We also marked the captive birds by

painting small, coloured signs with nontoxic paint (using Deco painter, Marabu, Germany) on their crown feathers to facilitate quick individual recognition during the observations. Birds were held in outdoor aviaries (approximately 5(W) × 4(L) × 3(H) m) in the zoo (Fig III.2).

Figure III.2. One of the aviaries (with attached hiding-place for observation) where we held the studied house sparrow flocks in captivity (photo by Á.Z. Lendvai)

In 2005, flock 1 and 2 were held separately in two aviaries ca. 5 m apart, with partial visual barriers (bushes) between them. Aviaries contained roosting trees and small boxes for sleeping and resting. Water, sand, and fine gravel (to facilitate digestion) were provided and multivitamin droplets were regularly added to the water. In order to be able to investigate social foraging tactic use in 2005 in Flock 1 and 2, feeding in these flocks took place on a grid (1.2 × 1.2 m) that contained 144 (12 × 12) equidistant wells (diameter 2.5 cm, depth 1.2 cm) for presenting food (Fig III.3; Lendvai et al. 2004).

Figure III.3. Sparrows became easily accustomed to the grid and used it successfully during social foraging (photos by Z. Tóth).

In 2006 in Flock 3, food was presented in three plastic bowls (diameter approximately 20 cm, depth 9 cm), each fixed on the top of a wooden pool (approximately 90 cm high). We provided millet, oat, wheat and sunflower seeds ad libitum during a 4-week acclimatization period and between different observations. The birds apparently became familiar with the aviaries during acclimatization, and they had also learned to use the grid by the time of the observations in Flock 1 and 2. Throughout the study, we did not observe severe aggression resulting in visible injuries, similarly to the previous studies on captive sparrow flocks (e.g.

Lendvai et al. 2004, 2006). Birds did not lose weight in captivity, their weight even increased slightly during the study (weight of all captive birds at the start of captivity [mean ± SE]:

27.85 ± 0.19 g; at the end of captivity: 28.23 ± 0.19 g; paired t test: t60 = −2.93, n = 61, P = 0.005). After the observations, we released all birds at the site of capture. To facilitate their survival after release, we provided bird food on feeders where we observed the released birds several times during winter. Some of them were also recorded as breeding adults in the following spring.