Marta Maziarz

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.

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.

Timing of breeding and nestling diet of Wood Warbler Phylloscopus sibilatrix in relation to changing food supply

Capsule Wood Warblers did not match their reproduction to the caterpillar peak Aims To study the timing of Wood Warblers’ breeding and nestling diet in relation to caterpillar abundance under primeval conditions in the Białowieża National Park, Poland. Methods Observations of food brought by parents. Inter‐year and seasonal changes in availability of folivorous caterpillars were assessed by direct counts and caterpillar frass collection. Results Maximum food requirements occurred two weeks after the peak of caterpillar abundance. The mismatch had no effect on nestlings’ development. Diet varied little across years and habitats, but varied strongly within a season. Following the decline of ‘green’ caterpillars, their proportion in the Wood Warbler diet strongly declined. Caterpillars were replaced by winged insects. Small nestlings received more spiders than older ones. Conclusion Timing of Wood Warbler breeding in Białowieża National Park was constrained by the females’ arrival time. Birds did not match their reproduction to the caterpillar peak. ‘Green’ caterpillars were the preferred food for nestlings; birds responded to the caterpillar decrease by feeding smaller proportions of them and switching to alternative prey, namely winged insects.

Microclimate of tree cavities used by Great Tits (Parus major) in a primeval forest

Altricial birds nesting in places with a favourable microclimate would be able to maintain the proper temperature of eggs or nestlings with less effort and thus reproduce more successfully. Tree cavities provide relatively safe nesting sites, but their microclimate is hardly known. Here we present the first data on air temperature and humidity in natural cavities used by Great Tits nesting in protected primeval forest in the Białowieża National Park (Eastern Poland). We checked what microclimatic conditions existed in cavities selected by Great Tits, how the construction of a nest changed the microclimate in a cavity and to what extent cavity localisation and cavity dimensions modified the microclimate of the breeding cavities. Great Tits used cavities in the living trees which were characterised by cool but relatively stable temperatures and very high relative humidity. Such conditions appear to be typical for cavities in living trees in general. Cavities with Great Tit broods were warmer and drier that the unused ones. The microclimate did not appear to constitute the major factor determining Great Tit usage of cavities in living trees, but it could exert a modifying effect on the pattern of cavity use by them. By choosing cavities of appropriate dimensions and placing the nest at an appropriate distance from the entrance, Great Tits could modify the cavity microclimate. However, their options were probably constrained by necessity to meet other important requirements, such as nest safety and illumination.

Natural nest-sites of Great Tits (Parus major) in a primeval temperate forest (Białowieża National Park, Poland)

Knowledge of the breeding ecology of the Great Tit Parus major is vast, but almost exclusively concerns birds using nest-boxes. Information on birds nesting in natural conditions is scant. Here, we present the results of the first thorough study on natural nest-sites of the Great Tit. The data, including descriptions of nest-cavity location and dimensions, were collected during 39 breeding seasons in the primeval forest of Białowieża National Park (BNP), Poland. With an excess of available tree-cavities providing a diverse choice of nesting options, Great Tits nested mainly in non-excavated, very deep and spacious cavities with elongated, narrow openings, placed at intermediate heights in living tree trunks. Different sets of tree species were used in different habitats. The pattern of nest-site utilisation by Great Tits in BNP overlapped with that recorded in other areas, but showed niche separation from other non-excavating hole-breeders in BNP. This indicates that Great Tits have core nest-site preferences, which have probably evolved in response to selective forces such as, e.g., risk of predation, flooding, sufficient nest illumination and/or efficient air ventilation.ZusammenfassungNatürliche Nistplätze der Kohlmeise in einem Urwald (Białowieża Nationalpark, Polen) Das Wissen über die Brutökologie der Kohlmeise (Parus major) ist sehr groß, bezieht sich aber fast ausschließlich auf Vögel, die in Nistkästen brüten. Informationen über Vögel, die unter natürlichen Bedingungen brüten, sind rar. Hier stellen wir die Ergebnisse der ersten umfassenden Untersuchung vor, die sich mit natürlichen Nistplätzen der Kohlmeise beschäftigte. Die Daten, darunter Beschreibungen der Lage und Dimension der Nisthöhlen, wurden während 39 Brutzeiten im Urwald des Białowieża Nationalparks (BNP) in Polen gesammelt. Bei einem Überschuss an verfügbaren Baumhöhlen, der eine vielfältige Auswahl von Nistmöglichkeiten zur Verfügung stellte, brüteten die Kohlmeisen hauptsächlich in natürlichen, sehr tiefen und geräumigen Höhlen mit länglichen, schmalen Öffnungen, in mittlerer Höhe von Stämmen lebender Bäume. In unterschiedlichen Habitaten wurden andere Baumarten gewählt. Das Muster der Nistplatzwahl der Kohlmeisen im BNP überlappte mit dem in anderen Gebieten aufgezeichneten, zeigte aber eine Nischentrennung von anderen Höhlenbrütern, die in natürlichen Höhlen brüteten. Das zeigt, dass Kohlmeisen grundlegende Nistplatzpräferenzen haben, die sich wahrscheinlich als Antwort auf einen Selektionsdruck entwickelt haben, wie zum Beispiel Prädationsrisiko, Überschwemmungsgefahr, ausreichende Ausleuchtung der Bruthöhle und/oder Ventilation.

40 years of breeding bird community dynamics in a primeval temperate forest (Białowieża National Park, Poland)

Abstract. We documented the composition and structure of the breeding bird assemblage in the primeval temperate forest of the Białowieża National Park (BNP), during 2010–2014, and used 40 years of data to assess patterns of its diversity. We applied an improved version of the mapping technique (a combined mapping method) for forest birds in seven plots located in three old-growth forest types: ash-alder riverine, oak-hornbeam, and mixed coniferous. The composition of the breeding avifauna and species richness remained basically unchanged. Jointly 67 (79% of 40-year total) breeding species were recorded in 2010–2014. Overall 49 (57%) of all species bred in the study plots in more than 35 years, they formed c. 97% of the pairs in the breeding assemblage. The composition of the group of dominants changed slightly; Phylloscopus sibilatrix became much less numerous in comparison to the earlier periods. Anthus trivialis ceased to breed — possibly due to disappearance of its habitat. The numbers of Sylvia atricapilla reached the highest ever level, and those of Columba palumbus and Dendrocopos medius equalled the maxima observed during 40 years. The overall breeding densities did not change significantly but they were substantially lower than in the peak year (2001). Crown insectivores, crown nesters and short-distance migrants remained the most numerous foraging, nesting and migratory groups, respectively. The earlier observed density gradient across habitats — highest in the riverine, lowest in the coniferous stands — was retained. Overall composition of the breeding avifauna did not change during 40 years, and no colonization of forest areas by a new species, nor extinction of a formerly widespread species, except A. trivialis, were observed. Some local changes of species richness occurred, however. Large-scale changes in coniferous habitats due to die-back of Picea abies and appearance of canopy gaps were followed by the increase in species richness there, while disappearance of former sharp forest edges reduced the number of species breeding in the “edge” plots. We suggest that the high constancy of species composition of the breeding bird assemblage in BNP results largely from the interplay of two factors: 1) long-term stability of the forest habitats, causing places suitable in one year to remain so over many seasons, and 2) cross-generational reproducibility of the selection criteria used by the birds in their settlement decisions.

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-site competition between bumblebees (Bombidae), social wasps (Vespidae) and cavity-nesting birds in Britain and the Western Palearctic

Capsule There is no evidence of widespread significant nest-site competition in Britain or the Western Palearctic between cavity-nesting birds and bumblebees or social wasps. Aims To investigate competition between cavity-nesting birds and bumblebees and wasps, particularly the range-expanding Tree Bumblebee, Saxon Wasp and European Hornet in Britain, and review evidence throughout the Western Palearctic. Methods We compared field data from English and Polish studies of tits and woodpeckers breeding in nest-boxes and/or tree holes to assess nest-site competition with bumblebees and wasps. We reviewed the literature quantifying nest-site competition between birds and these insects in the Western Palearctic. Results Bumblebees and wasps are capable of usurping small passerines from nests. In England, these insects commandeered a mean annual 4.1% of tit nests initiated in nest-boxes; occurrence of hornets showed a long-term increase, but not other wasps or bumblebees. Across the Western Palearctic, insect occupation of nest-boxes was generally low, and was lower in England than in Poland. No insects were discovered in tree cavities, including those created by woodpeckers (Picidae). Conclusion Nest-site competition between cavity-nesting birds and bumblebees and wasps appears to be a ‘nest-box phenomenon’, which may occasionally interfere with nest-box studies, but appears negligible in natural nest-sites.

Breeding microhabitat selection by great tits Parus major in a deciduous primeval forest (Białowieża National Park, Poland)

Capsule Great Tits breeding in natural cavities in a primeval forest occupied microhabitats containing larger trees, but small differences between ‘breeding’ and ‘non-breeding’ locations indicated the minor importance of microhabitat selection in nest-placement decisions. Aims We tested whether Great Tits breeding in primeval conditions used vegetation composition to choose breeding patches. Methods Great Tit territories and nest-trees were mapped in two study areas in deciduous, old-growth forest. We compared tree species composition, tree girth and condition between ‘breeding’ and ‘non-breeding’ plots. Results Great Tit territories were tightly packed, filling most of the available area. Vegetation composition in ‘breeding’ and ‘non-breeding’ plots differed only for trees that could potentially harbour Great Tit nest-cavities; ‘breeding’ plots contained larger trees. The distribution of Great Tit nests varied between years, with some ‘non-breeding’ patches in one year becoming ‘breeding’ ones in another. Conclusion It seems unlikely that nest-placement decisions by Great Tits are constrained by the microhabitat quality under primeval conditions.