Ring Ouzels don't like it hot

Submitted by Johan on 17 February 2021.

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As specialists of temperate mountain ecosystems in Europe, Ring Ouzels Turdus torquatus are expected to be particularly vulnerable to climate change. However, the underlying mechanisms by which drier and warmer conditions may affect the species are still unclear. In this study, we focused on the species breeding ecology to assess whether the nestling provisioning activity and efficiency were influenced by weather conditions.

Using camcorders, we monitored several nests during the period of chick rearing in the Swiss Alps. We revealed that the diet of the nestlings was composed mainly of earthworms, which constituted 90% of the fed biomass! Furthermore, we showed how warmer temperatures negatively impacted both prey provisioning rates and biomass delivered to chicks by parents, whereas rainfall had generally a positive effect on these parameters. As the breeding season progressed, the proportion of earthworms in the nestling diet decreased, with adults bringing smaller prey items. Our findings highlight the importance of prevailing weather conditions for the trophic and breeding ecology of the Ring Ouzel, and how those constrain reproduction to a narrow time window.

In the course of our study, we could not only monitor the provisioning activity, but also capture very interesting behaviours of Ring Ouzels on video that were not included in our paper.

For several broods, we documented the fledging event, i.e. the moment when a chick leaves the nest. Usually, the nestlings started to be more active already several hours before fledging, by stretching their legs, flapping their wings, and hopping on the nest edge before eventually leaving the nest:

 

 

On one occasion, however, fledging was less intentional. In effect, as nestlings grow, there is less space in the nest and more competition to access to the provisioned food, which can lead to small accidents. Hopefully, this nestling was old enough to fledge and his siblings also left the nest a few hours later.

Our video footage also provided insights into the social interactions between parental birds. Only the females (brownish plumage) were brooding the eggs or nestlings while both sexes took part in food provisioning. The adult female was however never fed by the male (black plumage), despite apparent begging displays. Moreover, we realized that adults systematically consumed faeces of the nestlings. The question remains whether this is driven by time constraints, nutrient intake, or predation pressure.

We also documented a male performing “whisper song” at the nest. The nestlings (not visible on the video) were only a few days old at this point and the function of this song remains unclear.

Carole Niffenegger & Arnaud Barras, first authors

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