Tomasz Wesołowski

The Breeding Bird Community of a Primaeval Temperate Forest (Białowieża National Park, Poland) at the End of the 20th Century

Abstract. The 1995–1999 results of the mapping technique censuses carried out in permanent plots situated in three types of old-growth primeval BNP stands (ash-alder riverine, oak-hornbeam, mixed coniferous) are presented and contrasted with the data gathered in the same plots in the late 1970s. Most community parameters, such as composition of breeding avifauna, species richness, make-up and cumulative proportion of dominants, remained basically unchanged. Only the overall bird density has increased considerably, by 13–38% in different plots. This has been due to parallel increases in numbers of several species, widely differing in their nesting sites, food requirements and migratory habits. As numbers increased simultaneously in all the plots, the density differences across habitats remained the same, from highest densities in riverine stands at the forest edge (up to 124 p/10 ha), through oak-hornbeam stands, to lowest in the coniferous stands (48–50 p/10 ha). Despite this differentiation the breeding avifauna in individual plots was quite similar (density similarity index exceeding 50% ), indicating that their breeding assemblages constituted samples from a single bird community. In most cases the numerical increases could not be attributed to changes in local environmental factors, such as food resources, weather conditions or changes in habitat structure. Only in the coniferous stands, could habitat changes leading to diversification of their structure (gap formation, increasing number of deciduous trees) have been responsible for increasing species richness and abundance there. The apparent lack of a relationship between changes in bird numbers and the local situation suggests that the factors acting on a larger scale (outside the study area) could have been involved. Despite the directional changes in bird abundance observed in the Białowieża Forest, its breeding bird assemblage, when compared with amplitude of changes recorded over the same period in other areas and habitats, stands out as an example of remarkable stability.

Breeding bird dynamics in a primeval temperate forest over thirty-five years: variation and stability in the changing world

Abstract. The composition and structure of the breeding bird assemblage in the Białowieża National Park (BNP) were documented in 2005–2009 and compared with the data from the previous 30 years. Mapping censuses were carried out in seven plots located in three forest types: ash-alder riverine, oak-hornbeam, and mixed coniferous forest. We checked whether the bird community composition had remained stable over the 35 years and the extent to which the numerical trends in BNP followed the regional trends. The composition of breeding avifauna and species richness was basically unchanged, except for the strongly increasing Sylvia atricapilla, which became a regular dominant in all habitats. The density gradient across habitats — highest in the riverine, lowest in the coniferous stands — was retained. After a maximum in 2001, the numbers of birds declined slightly, but densities were still among the highest in 35 years. Numbers of 18 of the 26 commonest species were higher in 2005–2009 than in 1975–2009; only Anthus trivialis, Phylloscopus sibilatrix, Ficedula parva showed negative trends, and Ficedula hypoleuca almost went extinct recently. Some numerical changes were attributable to local habitat changes (increases in Phylloscopus collybita and Sylvia atricapilla, declines in spruce-dependent species). Numbers of only four of 22 species (Dendrocopos major, Erithacus rubecula, S. atricapilla, Parus major) changed concurrently in BNP and the rest of Poland. The apparent lack of a relationship between changes in bird numbers and the local and regional situation suggests that factors acting on a far larger scale could have been involved. Despite these numerical changes, the breeding bird assemblage of primeval temperate forest stands out as an example of remarkable stability.

Breeding Bird Community of a Primeval Temperate Forest (Białowieża National Park, Poland) at the Beginning of the 21st Century

Abstract. The 2000–2004 results of the mapping technique censuses carried out in permanent plots situated in three types of old-growth primeval BNP stands (ash-alder riverine, oak-hornbeam, mixed coniferous) are presented and compared with data gathered in the same plots in the late 1990s. These data supplement earlier observations in the BNP and extend the long-term set of data on the breeding bird numbers there to a 30-year uninterrupted series (1975–2004). Most community parameters, such as the composition of breeding avifauna, the species richness, and the make-up and cumulative share of dominants, have remained basically unchanged. The overall bird density has increased by 8–20% in different plots; in 2001 it reached the highest level within the 30-year study period. The increase was due to parallel increases in numbers of several species, widely differing in their nesting sites, food requirements and migratory habits — during this period 14 of the 26 most numerous species attained their highest numbers in the 30-year study period. Since numbers increased simultaneously in all the plots, the density differences across habitats remained the same, from the highest densities in riverine stands at the forest edge (up to 149 p/10 ha), through oak-hornbeam stands, to the lowest densities in the coniferous stands (54–56 p/10 ha). In most cases the numerical increases could not be attributed to changes in local environmental factors, such as food resources, or to detectable changes in habitat structure. The apparent lack of a relationship between the changes in bird numbers and the local situation suggests that factors acting on a larger scale (beyond the study area) could have been involved. Despite the directional changes in bird abundance observed in the Białowieża Forest, its breeding bird assemblage, when compared with the amplitude of changes recorded over the same period in other areas and habitats, stands out as an example of remarkable stability.

Wood Warbler Phylloscopus sibilatrix: a nomadic insectivore in search of safe breeding grounds?

Capsule Wood Warbler population crashes coincided with local rodent outbreaks; arriving birds did not settle when rodent densities were high, apparently perceiving such conditions as too dangerous. Aims To look for causes of Wood Warbler nomadic behaviour, and to check whether local fluctuations were due to variation in weather, food availability or perceived predation risk. Methods Using long‐term data from Białowieża National Park (eastern Poland) we checked whether variation in Wood Warbler numbers and nesting success were related to temperatures during spring arrival, availability of folivorous caterpillars or to rodent numbers. Results Neither Wood Warbler numbers, nor rates of their change were correlated with temperatures. Numbers of birds were positively correlated with the numbers of caterpillars, but nesting success during caterpillar outbreaks was not especially high. High rodent numbers coincided with low Wood Warbler numbers and strong numerical declines of Wood Warblers. The expectation of higher nest depredation during the outbreaks was only partially confirmed. Conclusion The results are consistent only with the safety hypothesis: the arriving Wood Warblers refused to settle in rodent outbreak areas. Thus, Wood Warbler nomadic behaviour could result from their attempts to find safe breeding places.

Survival and population dynamics of Nuthatches Sitta europaea breeding in natural cavities in a primeval temperate forest

Data on breeding densities of Nuthatch were collected in three types of mature tree stands in Bialowieza National Park, E Poland, during 1975-90. Detailed observations on breeding and survival were made during 1987-89. The highest densities occurred in swampy stands (max. 4.8 territories per 10 ha), they were 10-47% lower in oak-hornbeam stands, and in coniferous stands densities did not exceed 1.2 territories per 10 ha. Nuthatch numbers reached a low in 1979, then increased over fourfold to a maximum in 1990. In contrast to the situation in Scandinavia, Nuthatch numbers in spring were not significantly correlated with the severity of the preceding winter, though their numbers seemed to be influenced by autumn seed supply and availability of caterpillars in the preceding spring. Yearly survival rates were close to 50%. Winter survival equaled that in spring and summer, and was even higher in the unusually mild winter of 1989/90 which had a rich supply of hornbeam seeds. Egg-laying in BNP commenced between 5 April and 26 April in different years. Clutches usually contained 6-9 eggs. On average two thirds of the nesting attempts resulted in fledged young, though nesting success varied much between plots. Nest losses were among the highest reecorded in European populations. Nests containing young were destroyed two to four times as often as nests with eggs, suggesting that the losses were mainly due to predation.

Changes in Breeding Phenology and Performance of Wood Warblers Phylloscopus sibilatrix in a Primeval Forest: A Thirty-Year Perspective

Abstract. The reproductive behaviour of Wood Warblers was studied in a primeval forest area in the Białowieża National Park (E Poland). Observations carried out during twelve seasons (1976–1979,1985–1988, 2002–2005) in deciduous and coniferous old-growth habitats spanned a 30-year period. The present paper examines whether the birds advanced their breeding dates during that time and whether any long-term shifts in fecundity or productivity were detectable. Though temperatures in the settlement period (the second half of April) rose, neither males nor females significantly advanced their dates of arrival. Wood Warblers bred earlier in 2002–2005 than in the two previous periods — the combined effect of earlier female arrival and shortening of post settlement breaks. Clutch size declined with season, was smaller in the coniferous habitat and in rodent outbreak years, but no long-term trend was perceptible. Apart from two exceptionally successful years (2003 and 2004) breeding losses remained high during the whole study. Predation was responsible for 80–95% of them and was concentrated on the nestling stage. Overall Wood Warbler phenology and breeding performance in BNP have changed relatively little during the last 30 years. These findings support the results of other studies demonstrating the remarkable resilience of this primeval forest biota to environmental change.

Time-saving mechanisms in the reproduction of Marsh Tits (Parus palustris)

Producing young late in the season is very costly in Marsh Tits, therefore any means which allow late-laying females to compensate for an initial delay are highly advantageous. Any attempts to make up for the initial delay should result in shorter breeding cycles late in the season and in shorter reproductive cycles in late-laying females. A shortening of the nesting cycle should be achievable via reduction of the clutch size or by shortening the duration of the incubation and/or nestling periods. These predictions are examined using data from an extensive study of Marsh Tits carried out in remnants of primaeval European forest (Białowieża National Park, E Poland). As anticipated, the breeding cycle late in the seasons was significantly shorter. This was due to a decline in clutch size, and shortening of the incubation period. The shortening of the cycle occurred also within a season, late-laying birds had significantly shorter cycles than early-laying ones. This was due to a very steep seasonal decline in clutch size and, to a lesser extent, by a shortened incubation period. With the five day overall difference, the late-laying birds could compensate for up to a third of the initial delay in egg-laying, a substantial saving of time. Young females commenced laying about two days later than older ones; as predicted, they laid smaller clutches but contrary to the predictions, they incubated for longer. The nestling period showed no relationship with season neither among years nor within a single year. Ein später Brutbeginn ist bei der Sumpfmeise mit hohen Kosten verbunden. Deshalb sollten sich Strategien zur Kompensation einer verspäteten Eiablage als vorteilhaft erweisen. Der Brutzyklus sollte in Jahren mit spätem Brutbeginn oder bei spät brütenden Weibchen innerhalb einer Brutsaison verkürzt sein. Dieses Ziel könnte durch eine geringe Gelegegröße und/oder durch eine verkürzte Brut- bzw. Fütterungszeit erreicht werden. Diese Hypothesen wurden anhand des Datenmaterials einer umfangreichen Studie an Sumpfmeisen im letzten europäischen Flachlandurwald (Białowieża-Nationalpark, Ostpolen) überprüft. Der Brutzyklus war in Jahren mit späten Bruten signifikant verkürzt, was sowohl auf eine geringere Gelegegröße als auch auf eine verkürzte Bebrütungsdauer zurückzuführen ist. Jedoch war der Unterschied von zwei Tagen verglichen mit der Variation des Medians der Eiablage von 19 Tagen zwischen den Jahren ziemlich gering. Die Verkürzung des Brutzyklus trat auch innerhalb einer Brutsaison auf; bei Paaren mit spätem Legebeginn war der Zyklus signifikant kürzer als bei frühen Paaren. Die Ursache dafür ist eine starke saisonale Abnahme der Gelegegröße sowie, weniger deutlich, eine verkürzte Bebrütungszeit. Mit einer durchschnittlichen Differenz von fünf Tagen konnten die spät brütenden Vögel ein Drittel der Verspätung kompensieren. Junge Weibchen begannen das Brutgeschäft etwa zwei Tage später als alte Weibchen und zeitigten kleinere Gelege. Entgegen der Ausgangshypothese bebrüteten sie die Eier jedoch länger. Die Dauer der Nestlingsperiode zeigte hingegen keine Beziehung zum Fortschritt der Brutzeit, d. h. Nestlinge aus frühen und späten Gelegen verlassen das Nest im selben Alter.

Effects of forest management on Three-toed Woodpecker Picoides tridactylus distribution in the Białowieża Forest (NE Poland): conservation implications

Abstract. Distribution of Three-toed Woodpeckers and that of dead wood were mapped in two fragments of the Białowieża National Park (BNP) differing in their management history — primeval (old-growth stands of natural origin, no human intervention) and logged (as the former but subject to 80 years of commercial forestry). Data were collected during the breeding seasons 1999–2001. In the end of April 2000, the whole BNP was systematically searched; playbacks of drumming were used to enhance detection of birds. Presence/absence of Three-toed Woodpeckers and of dead wood (standing and downed Norway spruces and snags of other trees) were recorded within each forest sub-compartments (ca. 28 ha). Data from censuses done in smaller plots in 1975–1999 showed that in the primeval forest the woodpeckers bred twice more frequently in swampy and coniferous forests than in the oak-hornbeam habitat. These preferred habitat types covered larger areas in the logged fragment than in the primeval part (66% vs. 41%). Yet despite this, Three-toed Woodpeckers were recorded there over twice less frequently (14% of 176 sub-compartments) than in the primeval (36% of 164 sub-compartments) part. These differences followed sharp contrasts in the dead wood availability; all but one sub-compartments in the primeval fragment contained some form of dead wood, whereas dead spruces were missing in almost 30% of sub-compartments in the logged part. This was the effect of continuous “sanitary” logging, purposeful removal of dying and dead spruces from the Forest. To restore Three-toed Woodpecker habitats it is necessary to ban removal of dead spruces in the managed part of BNP. However, the BNP area is too small, to assure the long-term survival of the Białowieża Forest population. To achieve this, it is necessary to resign from removal of dying and dead spruces in the whole Polish part of the Białowieża Forest (600 km2). This would create breeding habitat for a maximum 260–320 pairs.

Contrasting Patterns of Genetic Differentiation among Blackcaps (Sylvia atricapilla) with Divergent Migratory Orientations in Europe

Migratory divides are thought to facilitate behavioral, ecological, and genetic divergence among populations with different migratory routes. However, it is currently contentious how much genetic divergence is needed to maintain distinct migratory behavior across migratory divides. Here we investigate patterns of neutral genetic differentiation among Blackcap (Sylvia atricapilla) populations with different migratory strategies across Europe. We compare the level of genetic divergence of populations migrating to southwestern (SW) or southeastern (SE) wintering areas with birds wintering in the British Isles following a recently established northwesterly (NW) migration route. The migratory divide between SW and SE wintering areas can be interpreted as a result of a re-colonization process after the last glaciation. Thus we predicted greater levels of genetic differentiation among the SW/SE populations. However, a lack of genetic differentiation was found between SW and SE populations, suggesting that interbreeding likely occurs among Blackcaps with different migratory orientations across a large area; therefore the SW/SE migratory divide can be seen as diffuse, broad band and is, at best, a weak isolating barrier. Conversely, weak, albeit significant genetic differentiation was evident between NW and SW migrants breeding sympatrically in southern Germany, suggesting a stronger isolating mechanism may be acting in this population. Populations located within/near the SW/SE contact zone were the least genetically divergent from NW migrants, confirming NW migrants likely originated from within the contact zone. Significant isolation-by-distance was found among eastern Blackcap populations (i.e. SE migrants), but not among western populations (i.e. NW and SW migrants), revealing different patterns of genetic divergence among Blackcap populations in Europe. We discuss possible explanations for the genetic structure of European Blackcaps and how gene flow influences the persistence of divergent migratory behaviors.

Late leaf development in pedunculate oak (Quercus robur): An antiherbivore defence?

Abstract Two phenological forms of the pedunculate oak co-occur in the same habitats throughout the species range: the early trees (Quercus robur var. praecox) develop leaves up to 5 weeks before the late ones (Quercus robur var. tardiflora). This study tests the idea that late leaf flushing serves as an antiherbivore defence, i.e. late trees, which develop leaves asynchronously with eclosion of folivorous caterpillars, avoid the costs of defoliation, which could offset the costs of a later onset of the growing season. Effects of folivorous caterpillars foraging on oaks were observed in 1998–2006 in remnants of primeval temperate lowland forest preserved in the Białowieża National Park (eastern Poland). Observations covered trough and outbreak years of the major defoliator, the winter moth [Operophtera brumata L. (Geometridae)]. In seven out of nine seasons, including all peak caterpillar years, the amount of frass produced by folivorous caterpillars on late trees (n=8–18) was significantly (up to 7.1 times) lower than on the early ones (n=12–32). Assessment of the degree of defoliation in 2002–2006 showed that the late oaks were visibly defoliated only during a caterpillar peak (2003), while the early trees were affected in all years and in 2003 almost completely lost their leaves. The results confirm the effect of late budburst on lowering herbivore damage, and give support to the idea that late leaf flushing acts as an antiherbivore defence.