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Great Tits Outcompeted Blue Tits for Nest Boxes When Blue Tit Boxes Were Scarce

Great tit and Eurasian blue tit together
Research · Ecology

In Germany, competition within and between two closely related species interacted to shape breeding in Eurasian blue tits (Cyanistes caeruleus) and great tits (Parus major), according to an experiment published on 10 March 2026. By changing the availability of nest boxes intended for each species, the researchers experimentally altered breeding densities and tested how competition affected access to cavities and reproductive performance.

Breeding cavities proved to be a limiting resource. More blue tit pairs bred when the density of blue tit boxes was increased, and more great tit pairs bred when the density of great tit boxes was increased. The response showed that nest-site availability itself constrained how many pairs could breed.

Great tit competition changed where blue tits bred

When few blue tit boxes were available, increasing the number of great tit boxes led to more blue tits breeding in boxes intended for great tits. The authors interpret this pattern as evidence that great tits outcompeted blue tits for access to those cavities, changing the nest sites available to the smaller species.

The experiment also showed that competition within the blue tit population depended on how many great tit boxes were present. Blue tit clutch size declined as blue tit box density increased, but only when great tit box numbers were also high. Similar interaction patterns appeared in other important reproductive traits.

Competition was not simply a matter of total bird density

The effects differed significantly between the two species. The researchers conclude that competition among members of the same species and competition with another species cannot always be treated independently: changes in the density of one competitor can alter how strongly density affects reproduction in the other.

Sources and image credit

  1. Gaona-Gordillo, I., Białas, J. T., Cones, A. G., Dingemanse, N. J., & Holtmann, B. (2026). Intra- and interspecific competition interact: Multi-factorial experiments in two tit species. Behavioral Ecology, 37(3), arag026. https://doi.org/10.1093/beheco/arag026Primary peer-reviewed research article published 10 March 2026. A full-factorial manipulation of blue-tit and great-tit nest-box availability showed that breeding cavities were limiting and that intra- and interspecific competition interacted to affect blue-tit breeding density and reproductive performance.

Image: Georgi.petrov66 — great tit (Parus major) on the left and Eurasian blue tit (Cyanistes caeruleus) on the right in Botevgrad, Bulgaria, photographed 12 February 2022; Wikimedia Commons; representative image showing both study species, not birds from the nest-box experiment · CC BY-SA 4.0 · Source

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Ecology

SPECIES IN THIS STORY

Species in this story

Eurasian Blue Tit Cyanistes caeruleus Explore species Great Tit Parus major Explore species

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