Timing and Synchronisation of Breeding in a Marsh Tit Parus Palustris Population from a Primaeval Forest

89 TIMING AND SYNCHRONISATION OF BREEDING IN A MARSH TIT PARUS PALUSTRIS POPULATION FROM A PRIMAEVAL FOREST TOMASZ WESOLOWSKI Wesolowski T. 1998. Timing and synchronisation of breeding in a Marsh Tit Parus palustris population from a primaeval forest. Ardea 86: 89-100. Marsh Tits Parus palustris in Bialowieza National Park (E. Poland, 1985- 97) were single brooded, laid their first eggs between 5 April and 11 May (mean 21 April). Nest building commenced on average 10-15 days before the first egg was laid, but overlapped partially with egg laying. Median da tes of onset of laying in different years varied between 7 April and 26 April. Within a season laying was strongly synchronised as over 90% of birds commenced laying within ten days from the onset of the season. Early lay ing was correlated with high air temperatures. There were no differences in laying date between habitats. Females breeding for the first time on average laid two days later than in their following seasons. Otherwise, laying dates of individual females were repeatable between seasons. It is argued that the early and synchronised breeding of Marsh Tit is not so much an adaptation to the breeding season conditions but to a large extent a consequence of in tra-specific competition among young birds for a chance to settle, with ear ly fledged birds having strong competitive advantage. Key words: Parus palustris - Bilaowieza Forest - nest building - egg laying dates - weather conditions - nesting success - female age - repeatability Department of Avian Ecology, Wroc/aw University, Sienkiewicza 21, 50 335 Wroc/aw, Poland, E-mail: [email protected] INTRODUCTION much less intensively studied. This stems prob ably from the fact that they are much less numer Organisms living in seasonal environments need ous than Great or Blue Tits, and only infrequently to breed at the most suitable period for succesful use nest-boxes. Except of a recent series of Swed reproduction. It is generally believed that this pe ish papers (Nilsson & Smith 1988ab; Smith riod should be timed such that the young are re 1993ab; Svensson 1995), there are only single pa ared during the most benign period (Daan et ai. pers (Dunn 1976; Schmidt 1984; Berndt & Winkel 1988). Both ultimate and proximate aspects of this 1987) in which the Marsh Tit breeding phenology question have been intensively studied in Great is reported. The existence of the last fragments of Tits Parus major and Blue Tits P. caeruieus. The primaeval, European lowland forest preserved se studies have revealed a whole array of factors within the strictly protected part of Bialowieza such as photoperiod, weather conditions, climate, National Park (E. Poland, hereafter referred to as food availability, habitat, predation, social status, BNP) has provided a unique opportunity to study adult age, body condition, genotype that can in the biology of birds in conditions free of direct fluence, with varying intensities, the onset of human disturbance (Wesolowski & Tomialoj6 breeding (Blondel et ai. 1990, 1993; Perrins 1996). 1995). Marsh Tits breed there at low densities, 1-2 Marsh Tits Parus paiustris, although breeding in territories 10 ha- 1 (Tomialoj6 & Wesolowski 1990, similar habitats as Great and Blue Tits, have been 1996), in natural holes (Wesolowski 1996a). Here I 90 ARDEA 86(1), 1998 describe variation in the laying dates of Marsh heights and contain a large amount ofdead timber Tits at different temporal (between- and within and uprooted trees (Tomialoj6 et al. (1984), Fa season) and spatial (local population, individual linski (1986), Tomialoj6 & Wesolowski (1990, bird) scales in relation to weather conditions, hab 1994). Oak-lime-hornbeam stands (Tilio-Carpine itat, nesting success, sex, age and genotype. Fi tum, 44.4% of the BNP strict reserve) are most nally, the possible selective pressures shaping the structurally diverse. They are composed of a doz timing of the Marsh Tit breeding period are dis en or so species of trees (mainly Hornbeam Car cussed, as well as the proximate mechanisms pinus betulus, Small-leaved Lime TWa cordata, which could be responsible for adjustment of on Pedunculate Oak Quercus robur, Norway Spruce set of breeding to varying environmental condi Picea abies, Norway Maple Acer platanoides), tions. that vary greatly with regard to age and size. In several stands the canopy is formed by trees over 200 years old, and often exceeding 250-400 STUDY AREA years. The amount of dead wood is intermediate between that found in the swampy and coniferous The Bialowieza Forest complex is situated on the stands. Swampy deciduous stands (Circaeo-Alne Polish-Belarussian border, the western part (580 tum, Carici elongate-Alnetum, jointly 21.6% of km2, ca. 45% of the area) being in Poland. The the reserve area) are more uniform, with the cano Forest represents a remnant of the vast lowland py composed mostly of Alder Alnus glutinosa, forests that once covered large parts of temperate Ash Fraxinus excelsior and Norway Spruce. This Europe. Its present unique features result from its habitat type is characterised by the largest amount considerable size and a good conservation status of dead wood: there are about three times more (Falinski 1986; Tomialoj6 et al. 1984; Tomialoj6 & fallen logs there than are in the oak-hornbeam Wesolowski 1990; Wesolowski & Tomialoj6 1995). stands (Wesolowski 1983). The coniferous stands Though traces ofhuman presence are known from (28.1 % of area) are usually not inhabited by the Neolithic period, intensive timber cutting did Marsh Tits. not start before the beginning of this century. The majority of tree stands in the Polish part are now under management, but a block of the best pre METHODS served primaeval stands has been strictly protect ed within BNP. Data on Marsh Tit nesting were collected with The primaeval stands in the strict reserve of varying intensity during 1979-1997. Intensive BNP are distinguished by a whole array of fea searches for nests, aimed at finding the holes of tures. They are multi-storey, mixed-species, un all breeding pairs, were made in four deciduous even-aged, composed of trees reaching unusual areas (plots K, C, M, and W) in 1987-89 and Table 1. Study plots and forest types, including plot size (ha), main tree stands (%% after Wesolowski 1996a), and corresponding plot coding (Tom) as used by Tomialoje et at. (1984). Plot size forest type main tree stands Tom. K 33 ha riverine forest Ash,Alder K at forest edge C 48 ha forest interior S.-1. Lime (46%), Hornbeam (24%), N. Spruce (23%) CW,CE M 54 ha forest interior Hornbeam (47%), SA. Lime (27%), N. Spruce (13%) MS,MN W 50ha forest edge Hornbeam (34%), SA. Lime (28%), N. Spruce (18%) WE, WI Wesolowski: TIMING OF BREEDING IN MARSH TITS 91 1992-1997 (Table 1). The plots were 1-6 km son. This allowed us to compare individual birds apart. In other years nestholes were found mainly in consecutive seasons. After their first breeding during bird censuses carried out in the same four attempt, Marsh Tits are extremely sedentary, al plots (Tomialojc et af. 1984; Tomialoje & We most always staying in the same range for the rest solowski 1994, 1996). To determine breeding and of their life (T. Wesolowski, unpubl. data). Thus, nesting success, cavities were regularly checked, uminged birds settling in areas previously used mostly from the ground. Around the expected by ringed ones, are probably mostly young birds fledging date, they were inspected every 24 hrs. breeding for the first time. We therefore treated The day following the last day in which feeding uminged birds as young, first-time breeders. With of young in a hole was observed was taken as the this approach some older birds which had escaped fledging date. First egg dates were seldom direct catching in previous years will have been treated ly recorded in the field since, despite efforts to as first-time breeders. Note that the category of find nests at the building stage, numerous nests older birds is not so biased, as it contains only co were found only later. Moreover, even when a lour-ringed birds breeding for at least their second nest was found early enough, it was difficult to as time. certain whether laying already had commenced: Data on leaf-eating caterpillars, constituting nest cups were filled with wool around the laying an important source of nestling food, were col period and it was often not possible to see if they lected in May, the timing depending on the stage contained eggs. Therefore, it was necessary to of leaf development. Each time 50-120 standard back-calculate the first egg dates. To do this, it twigs (0.25 m2) from the lower parts of the horn was assumed that one egg is laid per day, that in beam undercanopy were searched and the cater cubation lasts 15 days, and that nestling age cor pillars counted. Original values of the caterpillar responds roughly to the stages given in Winkel index are given in Wesolowski & Tomialojc (1970) for Blue Tit. When clutch size and/or nest (1997). Meteorological data are from the local ling age were unknown (e.g. in holes observed weather station in Bialowieza village, situated in only from a distance or in holes containing only a the centre of Bialowieza Forest complex, less than single nestling), 40 days were subtracted from the 1 km from the southern edge of BNP (Wesolow fledging date. This comprised six days allowed ski and Stawarczyk 1991). To investigate the influ for egg-laying (a 7 egg clutch was assumed), 15 ence of spring temperatures on laying dates, fol days for incubation and 19 days for the nestling lowing Orell & Ojanen (1983), Schmidt (1984) stage (T.

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