The scary bright eyes of the Jackdaw

Jackdaws breed in loose colonies, and unusually for corvids, in cavities in trees, cliffs or buildings. There is often very strong competition for nest sites, and the pair will defend their nest fiercely against conspecifics. Jackdaws are also unusual for having very contrasting, almost white irides. In a recent paper, Gabrielle Davidson and her colleagues from Cambridge and Exeter Universities tested the hypothesis that the bright, contrasting eyes of the Jackdaw serve as a strong warning signal when adults are occupying a nest, warning intruders not to come in.
 They set up 80 identical nest boxes in woodland areas in Madingley (Cambridgeshire) during the pre-breeding season (February-April), when Jackdaws prospect potential breeding sites. The nest boxes had two perches, one at the base and the other just by the entrance. They fitted the inside of the entrances of the nest boxes with a circular printout, visible from the outside. Each nest box was randomly assigned one of four types of printout: a dark circle (control) a dark circle with white 'eyes'  of the same dimensions of a Jackdaw (eyes only), a printout of a face-on photo of a Jackdaw with eyes retouched to increase the brightness (bright eyes), and the same printout but with dark eyes (dark eyes). They used remote video cameras to record Jackdaw visits to the nests, and the time they spent sitting on the nest itself and the perches.
 The results were striking. Jackdaws alighted on the nest box significantly less when the bright eye print was in the nest entrance. In addition, they spent very little proportion of their visit time on the perch closest to the entrance both in the eye only and bright eye treatments. The visiting Jackdaws actually entered the nest box in two occasions, one in the control and another one in the dark eye treatment.

This experiment shows that eye colour can be important in communication with conspeficics. The pale eyes are a warning signal to prospecting Jackdaws that a nest is occupied, and they avoid approaching the nest entrance once they are on the nest box. This reaction to an occupied nest reduces intraspecific conflict, as it might save them from a fight and potential injury. Davidson et al speculate that the 'eye fear' response of Jackdaws might be more general, and they might react in the same way to sparrowhawk eyes, for example, as it is known that they are sensitive even to eye gaze in humans - they will delay their approach to food if a human is looking at them.

More information
Davidson GL, Clayton NS, & Thornton A (2014). Salient eyes deter conspecific nest intruders in wild jackdaws (Corvus monedula). Biology letters, 10 (2) PMID: 24501271

Tail flicking Moorhens

The contrasting white feathers at the sides of Moorhen tails are very obvious, especially when they flick their tails up and down, often fanned. As this one run away from me this morning I wondered what is this flicking for? An aggressive signal to other moorhens had been proposed as a hypothesis. However, observations carried out by Fernando Alvarez suggested a more intriguing reason. When a patrolling Marsh Harrier - a common predator - approached a moorhen, the rate of tail flicking increased as the moorhen dashed towards cover. In addition, the more vigilant the bird, or the further away from cover, the higher the tail-flicking rate was. These and other results suggested that tail flicking is not a signal to other moorhens, but a signal of alertness to the potential predator: 'I can see you!' This might deter the predator from chasing that alert individual and try catch a less vigilant one unawares.
 More experiments by Alvarez and colleagues suggested that moorhens in better physical condition showed higher flicking rates when foraging: healthier individuals flick their tails faster, which indicates that the signal is actually telling the predator: 'I can see you and I am fast so you can't catch me!
So both prey and predator would benefit from this honest signal of body conditions and alertness, as a chase, which would be wasteful in energy for the prey and likely to be unsuccessful for the predator, is avoided.

flicking away from me

she is definitely seen me!

she looks quite alert, but maybe then realised I pose no danger

UPDATE 3/10/2013

I took this video today of the tail flicking behaviour in the park moorhens

More information

Fernando Alvarez (1993). Alertness signalling in two rail species Animal Behaviour, 46, 1229-1231 DOI: 10.1006/anbe.1993.1315

Fernando Alvarez, Cristina Sánchez, & Santiago Angulo (2006). Relationships between tail-flicking,morphology, and body condition in Moorhens Journal of Field Ornithology, 77, 1-6 DOI: 10.1111/j.1557-9263.2006.00001.x