Patryk Rowiński

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.

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.

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.

Synchronisation of the autumn mass migration of passerines: a case of Robins Erithacus rubecula

Abstract. The pattern of autumn migration of the Robin was studied through an analysis of daily dynamics for the birds caught in the years 1984–1997 at four ringing stations (two on the Baltic coast and two in inland Poland). In a given year, migration dynamics was found to be distinctly similar at all stations. It showed conspicuous consistence (± 2 days) in the dates with peak numbers. This could be explained by assuming that Robins take off at the same time across a large breeding ground, and arrive almost simultaneously at stopover sites located over extensive areas. Moreover, migration dynamics from year to year at a given station was also remarkably similar, though this phenomenon was more distinct at the inland stations than at the coastal ones. Day-to-day fluctuations in numbers were on an average the highest at the coastal station most exposed to variable weather, the lowest at the inland stations, and intermediate at the more “sheltered” of the coastal station. The paper discusses the extent to which such results can reflect the influence of weather conditions on passage, or else a precise internal (physiological and genetic) mechanism responsible for the timing of migration.

Do Blue Tits Cyanistes caeruleus synchronize reproduction with caterpillar peaks in a primeval forest

Capsule Folivorous caterpillars constituted the majority of nestlings’ food in a primeval forest. Blue Tit broods only partially matched the caterpillar peak, and the mismatch did not affect food composition or nesting success. Aims To describe factors influencing the timing of reproduction in Blue Tits under primeval conditions (Białowieża National Park, Poland) and to check whether they schedule breeding so as to synchronize broods with a seasonal caterpillar peak. Methods We gathered information on phenology of leaf development, seasonal availability of folivorous caterpillars (frass collection), timing of Blue Tit breeding, composition of its nestling food, and nest fate over a three-year period. Results Caterpillars constituted c. 74% of nestling diet, but only 17–65% of broods matched the caterpillar peak in any season. Neither total nest loss, nor frequency of brood reduction depended on the level of mismatch. Caterpillar availability was probably adequate every year, regardless of the amount of mismatch, and no selective advantage of precise matching was detectable. Phenological events at all trophic levels occurred earlier in warmer springs. Egg-laying coincided with tree bud burst and appearance of caterpillars, but was not critically dependent on their timing. Conclusion The observations are consistent with the view that Blue Tits under primeval conditions in Białowieża National Park, Poland, breed as early as possible, rather than synchronizing their breeding with the caterpillar peak later in the season.

Interannual variation in tree seed production in a primeval temperate forest: does masting prevail?

We assessed seed production by mature individuals of five dominant tree species in the strictly protected reserve of Białowieża National Park (Poland) from 2002 to 2013. Interannual variation in seed production was extreme, generally asynchronous among species. All species exhibited high variability in seed production, ranging from bumper crops in some years to no seeds in others. All species exhibited a typical “normal masting” pattern, which was most pronounced in Picea abies and Quercus robur, moderate in Carpinus betulus and least expressed in Acer platanoides and Tilia cordata. Within species, crop sizes were well synchronised among areas and individuals; seed production was most synchronised in P. abies and Q. robur and least synchronised in T. cordata and A. platanoides within a season. Among species, interannual variability was negatively correlated with seasonal synchrony among individuals. Besides a negative correlation between rainfall during the flowering period and seed crop in three deciduous species, variation in temperature and rainfall in periods critical to seed formation was uncorrelated with the variation in seed crops. Heavy defoliation by caterpillars coincided with a poor seed crop of deciduous trees in 2003. Generally, the variation in seed crops was much higher than the variability of environmental factors. Deciduous species could produce bumper crops in consecutive years and were not necessarily forced to “switch” to non-reproduction by resource depletion. It appears that trees could apparently assess when and how intensively to reproduce. We discuss adaptive benefits of masting reproduction that include pollination efficiency, predator satiation and seed dispersal.

Nest Sites of a Strong Excavator, the Great Spotted Woodpecker Dendrocopos major, in a Primeval Forest

In managed forests, birds that create their own breeding holes in trees have limited access to substrates in which they can excavate. Therefore, nest site use in these forests possibly reflects availability of substrates more than species preferences. We analysed data on nest sites of Great Spotted Woodpeckers Dendrocopos major collected during 1987–2013 in the strictly protected part of Białowieża National Park in East Poland. The woodpeckers excavated breeding holes in 11 tree species, but species used in individual habitats varied greatly: Alder Alnus glutinosa was almost the only species used in the riverine forest; Aspen Populus tremula, Hornbeam Carpinus betulus and Pedunculate Oak Quercus robur were used most often in oak-lime-hornbeam forest, whereas Scots Pine Pinus sylvestris and P. tremula were used most in coniferous habitat. In oak-lime-hornbeam habitat, the birds strongly preferred to excavate in P. tremula and Q. robur, in the coniferous habitat the birds preferred P. sylvestris and P. tremula, and in all habitats Norway Spruce Picea abies and Small-leaved Lime Tilia cordata were clearly avoided. The woodpeckers generally excavated in large trees (median diameter at breast height: 50 cm), high above the ground (median 11 m), mostly in the trunks (83%) of living trees (67%). Overall, 21.7% of entrance holes were facing downwards. This pattern of hole placement is similar to that reported from other mature forests in Europe. We stress that despite very high plasticity in this species, it seems to use a distinct set of criteria for nest site selection that is related to predation risk, microclimate and mechanical damage of the place of excavation.