Monday, June 28, 2010

Passing Time with The Passerines

A guest post by Ken.

We are all familiar with the European Robin (Erithacus rubecula), that little friendly fellow at the end of the garden who is always quite out of reach and usually the first bird one has pointed out to as a child. A hard guy to catch but a bold fellow at that. However, in the New World they have their own robin. The American Robin.

So as I was taking a walk recently in Provo, Utah I spotted a bird which appeared to have an orange breast. I thought he was almost like our blackbird (Turdus merula) but a friend informed me later that he was, in fact, called the American Robin (Turdus migratorius).

Today I will discuss both.

Although both birds have orange breasts (the term 'redbreast' is associated usually with the robin and whilst it is an orange colour, this was considered red in the British Isles as 'orange' was not used until the introduction of the fruit of the same name), and both are passerine birds of the Order Passeriformes, the similarity ends there.

The European Robin has grey to brown upper parts and a white belly. It is a member of the Muscicapidae family or 'The Old World flycatchers'. It is found throughout Europe as far south as North Africa and as far east as West Siberia. It is approximately 13cm in length and weighs around 20g.

European Robin (Erithacus rubecula)

Male robins defending their feeding territory in winter do so aggressively but have low levels of testosterone, while males who defend a breeding territory in spring will have higher levels of testosterone. During both phases, song is an integrated part of territorial defense. Schwabl and Kriner suggest that the components of male robin song that are sung year-round as “keep out” signals are independent of testosterone, while the production of components that signal sexual information to females depends on testosterone, possibly augmenting the incorporation into and/or production of sexual components of the song. (Hubert Schwabl, Eva Kriner, Territorial aggression and song of male European robins (Erithacus rubecula) in autumn and spring: Effects of antiandrogen treatment, Hormones and Behavior, Volume 25, Issue 2, June 1991, Pages 180-194).

The American Robin is around the same length as our common blackbird (Turdus merula) at 23-28cm but is lighter at 77grams. It has a black head with white eye arcs and supercilia as well as a white belly. The back is usually brown in colour and the breast is orange although can appear slightly pink.

American Robin (Turdus migratorius)

It is a ubiquitous species in North America which has adapted to urbanization. The American robin and the grey catbird (Dumetella carolinensis) were the only species that remained present as the proportion of the land covered by houses went from 5% to 85%. The suburban environment, compared to woodland and farmland, is characterized by the presence of large patches of short grass, which are ideal for foraging throughout the breeding season. Morneal et al. found that American robins potentially can have a large clutch size and very high rates of reproductive success in suburban settings and that the breeding season seems to be of greater length in suburbs than in more rural areas. They suggest that suburbs may offer a greater variety and abundance of food and foraging sites due to the presence of more bare soil and areas where vegetation is kept short throughout the breeding season. Watering of lawns also mimics precipitation and favours the ascent of earthworms towards the litter. (Francois Morneau, Claire Lepine, Robert Decarie, Marc-Andre Villard, Jean-Luc DesGranges, Reproduction of American robin (Turdus migratorius) in a suburban environment, Landscape and Urban Planning, Volume 32, Issue 1, April 1995, Pages 55-62).

So there you have it. Robins. Both old world and new.



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