EUROPEAN STARLINGS (COMMON STARLINGS) FORAGING NEAR ICELANDIC HORSES, LAXNES HORSE FARM, MOSFELLSBAER, ICELAND, 7/6/2024

   I found this interesting article on the internet on why European Starlings (Common Starling) forage among horses.

Líffræðifélag Íslands - biologia.is
Líffræðiráðstefnan 2019

Erindi/veggspjald / Talk/poster V52

Starlings and horses – a case of commensalism?

Höfundar / Authors: Hrefna Sigurjónsdóttir

Starfsvettvangur / Affiliations: Háskóli Íslands

Kynnir / Presenter: Hrefna Sigurjónsdóttir

The habit of the common starling (Sturnus vulgaris) to forage close to horse groups and sit on the back of the horses has been noticed by birdwatchers and horse owners here in Iceland for some time and seems to be spreading. No references for this behaviour were found.
To get some idea of the functions of this behaviour, preliminary behavioural observations on the birds were carried out in Eilífsdalur, SW- Iceland, in summer 2018 in a pasture with a group of 26 horses. The birds were very movable: they frequently formed large flocks, landed a little distance from the horses for a short time, then came back and either settled on the horse´s backs (up to 20/horse) or landed on the ground. Looking closely at their behaviour it became clear that they were not feeding on parasites or skin flakes (one exception). Rather, they seemed to use the horse as perches to be on the outlook for predators, for a rest or as a site to spot where other birds were feeding. On the ground, they foraged for berries and invertebrates around the horses and interestingly also in the horse droppings. More data is needed to substantiate these results.
The horses did not shake their body to get rid of the birds nor were they aggressive towards them. This supports the idea that this association might be a case of commensalism- the birds benefit by getting access to more food while the presence of the birds for the horses is of no importance. However, in the evolutionary past when the horses' habitat was large plains and predators were a constant threat to the foals, an association with birds which spot predators quickly, might have been advantageous for both partners- hence a case of mutualism. Such a hypothesis has to be tested by observing reactions of the horses to the behaviour of the birds.