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35 years of studies

The main results of long-term studies (over 35 years) of (mostly) bird ecology and behaviour in primeval conditions have been recently summarised in a series of review articles. Their abstracts are available below, PDFs may also be requested.


Tomiałojć L., Wesołowski T. 2004. Diversity of the Białowieża Forest avifauna in space and time. Journal of Ornithology 145: 81-92.

The Białowieża Forest (BF) is an extensive and relatively little changed forest complex on the Polish-Belarussian border. Data on the structure and diversity of its breeding avifauna have mostly been collected in primeval old-growth stands, preserved within the Białowieża National Park (BNP). Mapping censuses repeated in space (plots, replicated in riverine, oak-linden-hornbeam and coniferous stands) and time (permanent plots, 28 years) reveal that the breeding bird assemblages are rich in species (29-52/season in a 25-33 ha plot), but of moderate overall density (40-120 p/10 ha). The latter due to low, lower than in man-transformed areas, densities of the majority of particular species. Despite marked changes in vegetation structure, the composition of the breeding bird assemblage does not vary much across different primeval forest types, a single breeding bird community inhabits all of them, including treefall gaps. High richness of the BF avifauna stems from the Forest's geographical localisation, as well as from a high level of the primeval avifauna retention. Over 95% of the 135-140 pristine species still breed there. Especially species-rich groups are birds of prey, owls, woodpeckers and Sylvinae warblers. Bird communities in the BNP and primeval tropical rain forests share many features, suggesting that natural differences between temperate and tropical forests were less pronounced in the past. The combination of high species richness with low densities of individual species is probably a feature of all pristine forests, independent of climatic zone. The BF avifauna must once have been typical of the ancient European forests and it has become so exceptional chiefly because it has preserved most of its pristine features. The BF constitutes, thus, an indispensable reference site for the future studies of woodland bird biology. To ensure its survival should become a priority. Commercial logging, taking place over 80% of the Polish BF part, severely changes the Forest's structure and strongly affects the birds, especially species which depend on dead wood (Dendrocopos leucotos, Picoides tridactylus) and on old-growth stands. The small area protected as the BNP becomes an increasingly isolated "island", in which preservation of the primeval forest features seems to be impossible. In order to retain them, it is necessary to protect the whole BF area


Tomiałojć L., Wesołowski T. 2005. The avifauna of the Białowieża Forest: a window into the past. British Birds 98: 174-193.

As a result of some 500 years of protection, parts of the Białowieża Forest in Poland, remain in a near-primeval condition. Studies of the breeding birds in the core part of the forest (Białowieża National Park) over 29 years show that bird community is species-rich but that densities of individual species are usually low, resulting in only moderate overall densities. In some species, low densities are a consequence of large territories and social exclusion, but often they reflect the undersaturation of habitats by birds, despite superabundant food supply and nest sites. Low productivity, resulting from high nest predation, may contribute to undersaturation. Species composition and numbers of birds fluctuate at BNP in relatively narrow limits, with the populations of closely related species fluctuating either independently of one another or in parallel; interspecific competition for resources plays a minor role. Some attributes of the Białowieża ecosystems resemble conditions in undisturbed tropical forests but contrast sharply with those in fragmented, temperate secondary forests. The present Białowieża avifauna provides a glimpse of that existing in central European forests before their historical transformation by humans. Its present exceptional character arises from preservation of most of its pristine features. The forest constitutes a critical reference point for studies of woodland ecology, and its preservation should be a high priority. Unfortunately, commercial logging continues, gradually changing the forest´s structure and affecting the birds, especially those dependent on dead wood and old-growth. the relatively small national park (47.5 km2) is increasingly becoming an ”island”, in which the long-term preservation of primeval forest features would be impossible.


Wesołowski T. 2007. Primeval conditions – what can we learn from them? Ibis 149, s2: 64-77.

In this paper I argue that prehistoric British forests and their avifauna were similar to those persisting in a near-primeval condition in the Białowieża Forest (Polish/Belarussian border). Therefore, observations in the Białowieża Forest may serve as a baseline against which effects of changes in the British woods can be assessed. The results of long-term (30 years) studies of the breeding birds in the Białowieża National Park are summarized. They reveal that the local avifauna shows some features (high species richness, low population densities, high nest predation and low production of young) regarded as typical for undisturbed tropical forests. It is proposed that high productivity, high population densities and sedentary habits found in many British populations are to a large extent a recent phenomenon, due to forest fragmentation, reduction of predator diversity and changes in forest structure. The necessity to preserve the whole Białowieża Forest – currently seriously threatened by ongoing logging– as a benchmark for future biological studies is underlined.


Wesołowski T. 2007. Lessons from long-term hole-nester studies in a primeval temperate forest. Journal of Ornithology 148, s2: S395-S405.

Nonexcavators (secondary hole-nesters) are birds that critically depend on holes for nesting and roosting; the absence of holes renders habitat uninhabitable to them. In man-managed woods, their populations are known to increase with the provision of nest-boxes, suggesting that the birds are limited by shortage of holes and must compete for them. I use 30 years of observations in the last fragments of primeval temperate forest of lowland Europe (Białowieża National Park, eastern Poland) to test these assumptions. They show that, in primeval forest conditions, (1) birds do not face a shortage of holes, (2) competition for nest sites is of minor importance, (3) woodpeckers are not keystone hole providers, and (4) nonexcavated holes provide safer nest sites than excavated holes. The Białowieża results are compared with studies from primeval forests on other continents. I conclude that in primeval forest conditions, hole-nesting nonexcavator birds are not, as a rule, nest-site-limited.


Wesołowski T., Cholewa M. 2009. Climate variation and bird breeding seasons in a primeval temperate forest. Climate Research 38: 199–208.

We investigated evidence for climate warming in the primeval forest of Białowieża National Park (E Poland) over the last 33 yr (1975–2007). We examined whether local populations of 4 sedentary birds (Sitta europaea, Poecile palustris, Cyanistes caeruleus, Parus major) advanced their breeding phenology during that time, and how breeding phenology was affected by temperature variation during the period preceding egg laying. Mean yearly temperatures varied strongly across years, with a significant warming (~1°C) trend. Spring temperatures increased significantly solely in the second half of April. Only P. major, which breeds later than the other species, showed a significant advance (~9 d) in breeding. Breeding dates of S. europaea and P. palustris, which usually lay eggs before mid-April, did not significantly change over time. In all species, the onset of breeding was very variable across years (up to 30 d), as birds started breeding earlier in springs with higher temperatures in the pre-laying period. Such a wide range of phenological plasticity indicates that the birds already possess mechanisms enabling them to accelerate breeding in response to climate warming, provided that warming occurs in the pre-laying period. All species shifted their laying dates concurrently; thus, the order of egg laying (S. europaea, P. palustris, C. caeruleus, P. major) was retained irrespective of the spring earliness. This also indicates that mechanisms allowing birds to respond to their changing environments exist at the community level.


Wesołowski T., Mitrus C., Czeszczewik D., Rowiński P. 2010. Breeding bird dynamics in a primeval temperate forest over thirty-five years: variation and stability in the changing world. Acta Ornithologica 45: 209–232.

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.


Wesołowski T. 2011. “Lifespan” of woodpecker-made holes in a primeval temperate forest: a thirty year study. Forest Ecology and Management 262: 1846-1852.

Woodpeckers, able to excavate holes in trees, can provide resources critical for non-excavator hole users. Supply of woodpecker-made holes in forests depends on excavation rates by the birds and holes’ persistence times. I use 30 years of data from a primeval forest (strictly protected reserve, Białowieża National Park, E Poland) to determine how long woodpecker-made holes persist, and whether their persistence varies across forest types, tree species and conditions, and woodpecker species. I followed the fate of 719 breeding holes, excavated by eight woodpecker species, for up to 27 years, from 1979 to 2010. Almost 80% of hole losses were caused by collapse of either the tree or the section supporting the hole. Holes were retained for (median) 6-7 years in riverine and oak-hornbeam forest but 10 years in coniferous forest. These differences can be explained by  almost completely non-overlapping sets of tree species used in these different habitats. Lifespan of holes varied by tree species, ranging from four (Picea abies) to >22 years (Pinus sylvestris, almost 100% dead). The long lifespan of holes in the dead Pinus was exceptional, as otherwise, persistence was much lower for holes excavated in dead trees or limbs (5 years) than for those in living substrates (9 years). Tree species with higher frequency of holes in dead wood showed lower persistence times of holes . Lifespans of holes excavated by individual woodpecker species varied widely and was strongly dependent on frequency with which the species excavated in dead wood. Holes of Dendrocopos minor and Dendrocopos leucotos (only in dead wood) persisted for four years, while holes of Dendrocopos major (able to excavate in living sapwood of some trees) lasted for nine, and those of Dryocopus martius for 18 years. Retention of dead Pinus sylvestris, decaying Quercus robur in stands and addition/retention of aspens (Populus tremula, Populus tremuloides) in them would provide conditions to increase the availability of relatively persistent woodpecker holes in forests of the Northern hemisphere.

Last Updated 18 November 2011