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STUDENTS AND POST-DOCS

BRANTA — Marta Maziarz


The nest sites’ characteristic and breeding success of Great Tit Parus major in primeval conditions (Białowieża National Park)

Institution: Laboratory of Forest Biology, Wrocłéaw University, Poland
Supervisors: Tomasz Wesołowski
Details: PhD 2012 (Completed)
Address: Laboratory of Forest Biology, Wrocłéaw University, Sienkiewicza 21, 50 335 Wrocłéaw, Poland (Mar 2013) Email
Subject Keywords: nest site selection, tree holes, breeding success, primeval forest
Species Keywords: Great Tit, Parus major

 

Abstract

I studied nest sites and breeding parameters of Great Tits Parus major in 2008-2011, in a primeval forest strictly protected within Białowieża National Park. My aim was to check which nest sites were used by Great Tits, whether the birds chose specific ones and – if they did – why? I presented the results in a 38-year perspective using archival materials gathered in 1975-2007 in BNP.

Great Tit is a non-excavator. This species depends on the presence of different holes (non-excavated – created by wood decomposition, and excavated by woodpeckers), where it nests. Knowledge of this species’ biology is extensive, but it originates almost solely from studies in artificial nest sites – nest boxes. The birds nesting in these sites meet other problems than in natural conditions. In consequence, there are drastic differences in reproduction and mortality between individuals breeding in nest boxes and tree holes. Information on natural nest sites of Great Tits are scanty, similarly, the data on their broods in tree holes rare. Still, we do not know which factors affect Great Tits’ decisions and what might be the fitness consequences of using different types of holes by them.

Because asked questions are functional (survival of brood and parents depends on nest site quality), to understand Great Tits’ nesting adaptations, studies in conditions similar to which they presumably had adapted, are required. Such primeval conditions have been preserved in strictly protected part of Białowieża National Park. There, among other things, the birds find an abundance of diverse nesting sites and rich food resources, but – simultaneously – they are exposed to strong predation pressure.

I expected, that in BNP, predation would be the most frequent cause of Great Tits’ brood losses, and safety the main criterion of nest site selection by this species. Some holes would be safer, but using them would be limited due to insufficient illumination, unsuitable microclimate (too high or too low temperatures, higher humidity) or higher risk of flooding.

To characterize nest sites used by Great Tits, I described forest structure (for comparison, in settled and unsettled fragments), hole location in a tree and measured dimensions of tree-holes utilized by this species. I also measured air temperature and humidity (for comparison in used and unused holes) and light intensity at the nest’s level. To find out the brood size and breeding success of Great Tit, I aimed at finding nests of all breeding pairs on plots (located in oak-hornbeam habitat). All nests found were systematically checked till destruction or fledging.

Great Tits, having an access to the wide spectrum of holes, used specific nest sites similar to those utilized in other parts of Eurasia. That indicated the existence of nest site preferences of the birds. According to previous conjectures, the main cause of Great Tits’ brood losses in BNP was predation. The safest appeared non-excavated holes, placed in living parts of trees, lower above ground, with smaller openings and greater depth. Those sites were most commonly used by tits. Almost all birds avoided larger predators (e.g. martens, woodpeckers), which were unable to enter the holes nor pull out the contents outside. Yet, the openings of tree-holes used by Great Tits did not constituted barrier for the smallest predators (chiefly Forest Dormouse Dryomys nitedula) which could easily pass through the narrowest entrances. However, the birds could avoid small predators by nesting much further from the entrances and lower above a ground. Yet, they were not able to escape from them totally. Using ‘predator-proof- holes would bear other costs. Extremely deep holes with small openings would be too dark to be used. While, in holes placed lower above a ground the risk of flooding might be greater. The birds using them would be exposed to much lower temperatures which presumably would increase costs of incubation and heating of small nestlings. In consequence, the decisions made by Great Tits were compromises between conflicting demands (safety, sufficient illuminance and protection against flooding).

In Białowieża National Park Great Tits used – first of all – safe holes, because that the most increased their fitness. Nevertheless, selection of those sites was constrained by other factors which could be dangerous in extreme situations. Most commonly used holes provided optimal conditions for breeding, though despite that, broods over half of breeding pairs failed. It seems that Great Tits reached their adaptative optimum (changes in any direction probably would lead to decreases in fitness).

 

Published Papers

Maziarz M., Wesołowski T. (in press) Microclimate of tree cavities used by Great Tits (Parus major) in a primeval forest. Avian Biology Research.

Wesołowski T., Maziarz M. 2012. Dark tree cavities – a challenge for hole nesting birds? Journal of Avian Biology 43: 454-460.

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