Stanisław Kuźniak

What affects the magnitude of change in first arrival dates of migrant birds

We analysed which among four factors (mean first arrival date, migration distance, changes in population size, detectability of species) influenced the magnitude of change (regression coefficient) in the first arrival dates of 30 migrant bird species in western Poland during 1983–2003. An examination suggested that several of these factors could be important: the regression coefficient was positively related to mean first arrival date (early species advancing their arrival date more) and negatively with change in population size (species in decline changing less). Moreover, significant differences in regression coefficient were detected between short and long distance migrants and between low detectable and highly detectable species. Undertaking a principal components analysis on the four factors produced an axis explaining 59% of the variance and whose positive values were associated with late arriving, long distance and low detectable species which were more likely to be in decline. However, the multi-collinearity of these factors is a problem that cannot be resolved here and we recommend that further work from different areas is needed to tease apart these effects.

Bird Migration Advances More Strongly in Urban Environments

Urbanization has a marked effect on the reproduction and other ecological and behavioural traits of many living organisms, including birds. In migrant birds, survival and reproductive output is influenced by the (mis)synchronization of arrival with the availability of resources. Many recent studies have shown that arrival timing is related to temperatures en-route and at destination. Because urban areas are “heat islands”, with higher temperatures that influence earlier vegetation and invertebrate development, this should favour earlier arrival of migrant birds to cities rather than to rural areas. In this paper, we analysed differences between urban and rural habitats in mean dates and trends of first arrival dates of 18 species of migratory bird species in western Poland during 1983–2010. For many individual species, and overall, mean first arrival date was significantly earlier in rural areas than in urban areas (significant for 11 species). However, the trend towards earlier first arrival dates was stronger in urban areas for 15 of the 18 species (significantly stronger in four species). Consequently, arrival dates in urban areas are fast approaching, or have now matched or passed those in rural areas. These findings suggest that recent environmental changes may have more rapidly changed the migratory habits of birds occupying urban habitats than those occupying rural habitats.

Long-Term Changes and Breeding Success in Relation to Nesting Structures used by the White Stork, Ciconia ciconia

Anthropogenic changes have strongly influenced the European landscape. In the last 50 years electric power-line networks have become a conspicuous part of that landscape. From the outset it was known that these lines and their support structures would cause fatalities in the white stork, Ciconia ciconia. From a long-term (1983–2006) study in Poland, we analysed breeding performance in stork nests on four types of structure (chimneys, roofs, trees and electricity poles). Whilst the numbers of nests on both electricity poles and chimneys have increased, there was no significant difference among the four structures in terms of breeding success. Since 1998, over 100 electricity poles in this white-stork breeding area have been modified to include a platform designed to accommodate a stork nest. A comparison between the annual means of nests on electricity poles with and without platforms did not reveal any significant differences in breeding success. However, closer examination of the nests transferred to platforms revealed a slight drop in chick productivity in the year following platform addition, which, however, became significantly higher in the subsequent year. Thus the transfer of nests to platforms appears to have only a short-term adverse effect and may be beneficial in the long run.

Should avian egg size increase as a result of global warming? A case study using the red-backed shrike (Lanius collurio)

From some life-history traits, avian egg size can be postulated as potentially affected by climate change. In this paper, we present and discuss the potential effect of mean temperature in the breeding season on egg size of the red-backed shrike (Lanius collurio). During the 1971–2002 study period, egg volume of the red-backed shrike decreased significantly, birds arrived at the breeding site significantly earlier, and arrival date was correlated with the earliest first egg date. To our knowledge, we present the first evidence that avian egg size decreased significantly in a long-term study. However, we do not have experimental manipulations in support of our data and we can only conclude that the decrease in egg volume in the studied population might result as a consequence of a number of factors, including changes in temperature, as well as in food supply. Therefore climate change effects on a bird’s life-history traits can be more complex than just the simple direct effect of temperature.

Disperse or Stay? Exceptionally High Breeding-Site Infidelity in the Red-Backed Shrike Lanius collurio

Nesting in the same breeding area in successive years provides information to help understand the cues used by birds in habitat selection. Moreover, such information may also be an important tool for the conservation and management of endangered species. Based on the ringing results of 122 adult and 1245 nestling Red-backed Shrike Lanius collurio in the years 1996–2005, we studied philopatry of the species in two different populations: in western and in eastern Poland. Moreover we analysed all Polish Red-backed Shrike ring recoveries since 1996 (n = 3102 ringed birds). We noted that both natal and breeding philopatry in the populations were almost entirely absent. This is surprising in comparison with other studies, especially those including shrikes. Comparisons with other populations suggest that the lack of philopatry is not related to the breeding success of local birds and/or the size of the study area. In contrast, we suggest that low philopatry is an effect of and/or an adaptation to a relatively high population density at the land-scape scale, where many breeding areas and potential nesting sites still remain vacant.

New is not always better: low breeding success and different occupancy patterns in newly built nests of a long-lived species, the white stork Ciconia ciconia

Capsule An increase in new nest building in a white stork population revealed that they were built further from human settlement and on non-typical structures; such nests had lower breeding success resulting from later breeding. Aim To determine why some birds build new nests rather than occupy older ones, and how new nests affect breeding performance compared to old nests, in a long-lived bird, the white stork. Methods We compared new nest construction in 2010 with a long-term data set on white stork in Western Poland from 1974 to 2009. For data from 2010, we analysed nest location and breeding biology in detail. Results Since 1974, the proportion of new build nests was ca. 1.6%; in 2010 this was 13.2%. Pairs in new nests bred later than pairs in old, and had smaller clutches and lower breeding success. New nests were located further from settlements and tended to be built on different structures. A significantly lower proportion of new nests were re-occupied in subsequent years. Conclusions Pairs may build new nests to gain experience in nest building, cooperation and foraging for subsequent seasons or because of competitive pressure when the environment is close to carrying capacity. Breeding success can be initially very low.

The relationship between population means and variances of reproductive success differs between local populations of white stork (Ciconia ciconia)

We studied the size and productivity of white stork (Ciconia ciconia) populations in eight study sites in Poland. The number of nesting pairs and the average number of chicks fledged per pair fluctuated over time, and the studied populations differed in the variance of both breeding success and number of breeding pairs. The variance of breeding success (both for the mean number of chicks and the proportion of successful nests) and the variance of the number of breeding pairs was not correlated with the extent of stable habitats (pastures, meadows, wetlands), other habitats (farmland), or with local population trends over time. We found a non-linear symmetrical relationship between annual mean reproductive success and its variance but only when considered as the proportion of successful nests (i.e., when individual nests are coded as a binary value: 0, no success; 1, success). No such relationship existed when success was expressed as the number of fledged chicks. Although a positive significant correlation occurred between fledgling numbers (discrete data) and the proportion of successful nests (binary data), we believe that the use of only binary data will be inadequate in more detailed analyses, such as population viability analysis.

Costly replacement: how do different stages of nest failure affect clutch replacement in the red- backed shrikes Lanius collurio?

Re-nesting is costly and strongly stage- and time-related in the redbacked shrike. We tested whether failure which occurred at more costly developmental stages of the first clutches influenced the characteristics of replacement clutches in red-backed shrike Lanius collurio. Field work was conducted in the breeding seasons 1999–2006 at three study plots in Poland. During nest visits, standard data on breeding biology were collected, including clutch size, eggs measurements, laying date, and number of nestlings. We found significant differences in the clutch size of replaced clutches according to the failure phase of first clutches. Pairs which experienced brood failure at the nestling phase produced smaller replacement clutches than pairs whose nest was destroyed at the egg laying stage. There were no differences in the nesting success of replaced cluches relative to the stage where the first clutch was lost. However, pairs which failed during the nestling phase of the first clutch significantly more often skipped further reproduction in that season than those which failed during other phases. For breeding red-backed shrikes the best strategy is to initiate clutches as early as possible because it gives a more time for possible re-nesting.

Spatial and Temporal Relations between the Barred Warbler Sylvia nisoria and the Red-Backed Shrike Lanius collurio in the Wielkopolska Region (W Poland)

Abstract. The Red-backed Shrike and the Barred Warbler are a pair of species engaged in breeding association. Whilst the arrival time of both species from their wintering grounds was not correlated, they differed in median arrival time by only one day. The majority of the Barred Warbler territories were located within those of the Red-backed Shrike, in both forest and farmland plots. Both species differed significantly in their selection of nest sites, at least in farmland. Unlike to the Red-backed Shrike (n = 297), the Barred Warbler (n = 60) preferred blackberry bushes and small deciduous thornless shrubs, and avoided elder, coniferous and hawthorn. The Barred Warbler nests were placed significantly lower than those of the Red-backed Shrike. The results show that no special ecological relationships exist as was suggested in earlier papers for other areas.