Thursday, April 28, 2011

I like my Opal Fruits with the wrappers on

Gulls in Aberdeen are well known for cleaning up all the food detritus left by humans, even if they do get a little over-excited on occasion and enter shops to steal Nik-Naks crisps or snatch chips from unsuspecting tourists. At the weekend I observed a Herring Gull (Larus argentatus) tucking into a forgotten bag of Starburst (aka Opal Fruits), wrappers and all! Since gulls probably have limited olfactory senses they can’t enjoy the rainbow of fruit flavours anyway! ... wait, that was the catchprase for Skittles, but no doubt they’d try them too.

Wednesday, April 20, 2011

Iberian Water Frog Chorus

Well its been a while since my last post! Earlier this month I was in south-west Spain for eleven days on an annual ecological genetics field course (a 2nd year undergraduate course) based around Zahara de los Atunes, near Tarifa. One of the study sites is the Arroyo del Tiradero in Parque Natural de los Alcornocales, a beautiful mountain stream where students study mate guarding in the pond skater (or water strider) Aquarius najas. Our particular stretch is lined with alder trees and surrounded by cork oak dehesa-like habitat. Interesting bird species here include Iberian Chiffchaff, Western Bonelli's Warbler, Short-toed Treecreeper, Cirl Bunting, Firecrest and Hawfinch, while there is often a spectacular array of raptors overhead. As well as being fantastic for bird song, at least when the wind is not blowing, there is an almost constant chorus of singing Iberian Water Frogs (Rana perezi) at this time of year. The vocal output tends to fluctuate from quiet periods when just one or two individuals are singing to almost deafening (at close range at least) crescendos during communal displays involving many frogs. This is likely to be lekking behviour (Ruff and Black Grouse being good examples in birds) but it is difficult to approach these frogs to closely observe them as they either go silent, or dive underwater.

Saturday, April 02, 2011

Eurasian Crane Unison Calls

We often read of Crane vocalisations described as ‘bugling’ or ‘trumpeting’ but I recently found a paper in the Journal of Comparative Physiology by Gaunt, A.S. et al (1987) that suggests that rather than comparison with a wind instrument, a better analogy would be with a stringed instrument such as a violin. Through experiments involving surgery of the trachea, or wind-pipe (I wonder if this sort of work still occurs today?) they found that the syrinx (the avian voice box) works like the ‘strings’ resting on the ‘bridge’ of an instrument, in this case the crane’s trachea (acting as a resonator), with the vibrations transferred to the sternum (breast bone). The sound is further amplified as the sternum is connected to a system of air sacs. Looking at pictures of the anatomy of the crane trachea, I had no idea it was so coiled.

I recorded the unison calls from a pair of Eurasian Cranes (Grus grus) in Sweden last year and if you listen to the sound file and look at the sonogram you can hear the harmonic sounds produced from both sexes during display. The male utters the single, longer call (lowest, or fundamental, harmonic between 0.65 - 0.90 kHz) lasting around 0.6 seconds with the female duetting with two shorter, slightly higher-pitched calls (lowest harmonic 0.95 - 1.15 kHz) lasting around 0.15 seconds. I was in a small hide just metres away from the pair and the loudness and intensity of crane vocals at this range was amazing. Quite different is hearing a pair at long range, echoing over a northern bog when the sound becomes evocative and beautiful… and I’ll post more on this later.