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Spotless starling (Sturnus unicolor) breeding colony


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Spotless starling (Sturnus unicolor) breeding colony

Since 2002 we have been following a spotless starling population in a woodland near Madrid. Some 250 nest boxes are in use at the moment, with a very high occupancy rate.

Spotless starlings are medium-sized passerines, with a complex breeding strategy which includes facultative polygyny, intraspecific brood-parasitism, many floaters, and a high rate of nest sabotage, including infanticide. Most pairs manage two annual broods, and the modal clutch size is 5 eggs.

There is a high adult survival and philopatry rate (60%), something that allows a good follow-up of the birds throughout their lives, and accurate estimations of their life-time reproductive success. On the other hand, the recruiting rate for first year olds is also high (15%), and this is particularly relevant for studies that explore how early life conditions determine effects in adults.


An intensive ringing campaign at the nest boxes takes place every year, two months before the laying season, and this allows capturing most of the adults present in the study site. We take extensive biometrical data, plumage colouration, behavioural observations, and blood samples from which physiological data can be gathered.

We fit adult birds with miniature microchips under the skin so that we can follow the bird behaviour at the boxes without further trapping. To do this, we count on microchip readers (TROVAN) which are routinely set in the boxes and provide us with a good activity estimate before and during laying, nestling feeding etc. In addition we use mini infra-red camaras to study nestling begging behaviour.


  • Young female spotless starling
  • Tonic immobility in a starling
  • Hungry chicks
  • Nestbox
  • Nestling (14 day old)
  • Nestlings (six-day olds)
  • Field site