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12 of 17 Male Eurasian Wrens Kept Winter Territories Into the Breeding Season

Eurasian wren perched on a branch in Japan
Research · Behaviour

Male Eurasian wrens (Troglodytes troglodytes) remained territorial at a mountainous breeding site in Japan through the non-breeding season, according to a study first published online on 9 March 2026. Of 17 wrens that showed clear territorial behaviour during winter, all were identified as males, and 12 were still defending territories during the following breeding season.

The fieldwork was carried out in Ashiu Research Forest in Kyoto, where the study area followed about 5.5 kilometres of rivers and streams at roughly 650–700 metres above sea level. Winter surveys ran from 9 November to 14 December 2023, followed by breeding-season observations from April to July 2024.

Winter territories were defended with calls rather than song

The researcher used playback of the wrens’ short “tic” calls to locate and map winter territories. These calls were frequently used during vocal interactions between birds in winter, in a role similar to territorial song during the breeding season.

The 17 territorial birds were later sexed from breeding behaviour or molecular analysis, and all proved to be males. Twelve retained territoriality into the breeding season. Five were no longer observed, while six additional males that had not been recorded during winter established territories after the breeding season began.

Most returning males expanded their territories

Across all males, mean territory length was about 155 metres in winter and 206 metres in the breeding season, a statistically significant difference. Among the 12 males that retained territories across both periods, however, the change in territory length was not statistically significant. Eight of those 12 males expanded their territories.

The author suggests that defending a territory during winter may allow males to secure breeding sites earlier. In this polygynous species, males with higher-quality territories may have a better chance of attracting more than one female. Whether winter territoriality actually improves later reproductive success is now being tested.

The results show that territorial competition at a breeding site can begin months before the breeding season itself. The author notes that the study covered only one year and that longer-term observations are needed to determine how consistently the pattern occurs.

Sources and image credit

  1. Soda, A. (2026). Male-specific territoriality and use of specific calls during the non-breeding season in the polygynous Eurasian Wren Troglodytes troglodytes. Ardea, 113(2), 251–258. https://doi.org/10.5253/arde.2025.a17Primary research article. Kyoto University confirms that the paper was first published online on 9 March 2026, despite the Ardea issue carrying a 2025 bibliographic label. Seventeen wrens showed territorial behaviour in winter; all were males, and 12 maintained territories into the following breeding season. The article is available under CC BY-NC-ND 4.0.
  2. Kyoto University. (2026, March 19). 冬の山でなわばりを守るミソサザイ―繁殖なわばり争いは非繁殖期に始まっていた― [Wrens defend territories in winter mountains].Official university research release confirming the 9 March 2026 online publication date and summarising the winter-territoriality findings.

Image: M. Nishimura — Eurasian wren of the Japanese subspecies fumigatus (Troglodytes troglodytes fumigatus) in Japan, photographed 29 February 2008; Wikimedia Commons; representative Japanese subspecies image, not one of the individually marked birds from Ashiu Research Forest · CC BY-SA 3.0 · Source

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