Sunday, 5 May 2013


(Originally at FB Osprey Webcam Group)

(c) There are no ospreys on the Indian sub-continent 

FALSE. Ospreys are still reported from India and Bangladesh, where they appear to be coastal, confined to specific areas and not common anywhere. One hot spot seems to be the Sundarbans wetland in Bengal, where ospreys are regularly spotted by visitors. The most recent sighting I could find was 2/2/2013 and this photo by Nazul Islam was taken in 2010.
Osprey at Sundarbans lagoon. (c) Nazul Islam 2010
The population appears to be migratory and there have been a few ring recoveries – one from a bird originally ringed in Norway. In their survey in the 1980's, Sakeur & Sakeur listed ospreys as one of 14 raptor species known to be in decline, citing habitat loss as the major factor in all cases.

Things must have been different in the recent past... A young Army officer named Elliot, on posting in the Punjab, complained to his diary of 1891 that there were no interesting or exotic birds on and around the lake outside his kitchen window, “...only the usual ospreys, everywhere to be seen.”


(d) GPS bird tracking devices are less accurate when it's raining.

Pretty accurate: Niacom active antenna with Garmin Q3600 using SBAS differential corrections for a combined error of less than 2 metres

FALSE. Occasionally, I am asked to explain to someone exactly how the Global Positioning Satellite System works. I try to avoid this, because usually the explanation is only a quarter way through before the “someone” has fallen into a deep and restful sleep. The GPSS is one of those things like Corporation Tax, or the Immaculate Assumption, or open heart surgery – if you needed to know how it works, you would already know exactly how it works.

The space-to-ground segment of GPS is a radio signal. In fact, two primary radio signals, known as the “L1 and L2 carriers.” When the system was being designed, the wavelength for this signal (20cm L-band) was carefully chosen because these frequencies are least likely to be affected by water vapour in the atmosphere. Clouds and rain have no measurable affect on GPS accuracy, although many internet “experts” will still try to tell you that this happens. The myth probably arose because people that are carrying GPS -equipped smart phones might take shelter from rain under structures or dense foliage. These local obstructions could have some effect on reception, but the rain itself does not.


(e) Ospreys don't like flounders because they taste funny and are the wrong shape.

FALSE. Poor flounders... rejected by chefs, despised by ospreys, and as ugly and stupid as Ian Duncan-Smith, they get a universally bad press. The fact that ospreys don't like them is well supported by data, though it might be truer to say that while ospreys are prepared to eat flounders – they'd just prefer to eat other things instead. But why? Well camouflaged bottom-feeding flounders are abundant around the British coast in summer, and you'd think they would be perfect sustenance for a nest full of baby ospreys.

The best theory we have is to do with net energy inputs. Compared with other seasonal estuarine species ( e.g. mullet, bass, sea trout) the flounder has about 8-10% less fat content. And for birds, as we all know, fat = flight fuel. Emyr Evans (who is not keen on eating flounders himself) has pointed out to me that they have tougher skin than these alternative species, and so the upshot of all this is a three-way disadvantage in terms of diet:-

  • More difficult to catch,
  • More energy expended dealing with the food,
  • Less energy obtained after ingestion.

Put together, this would explain why the birds – especially breeding females – have evolved a preference for more energy-rich prey items. Shape and taste are unlikely to have much to do with it.

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