RFI: Gerygones, thornbills etc. drinking

To: "simon starr" <>, <>
Subject: RFI: Gerygones, thornbills etc. drinking
From: "Stephen Ambrose" <>
Date: Mon, 5 Mar 2007 07:03:47 +1100
Hi Simon,

Acanthizids (and probably many other small Australian insectivorous birds) appear to get most of their water from their invertebrate diet, which is high in water content. Drinking water is also obtained from early morning dew that is deposited on the vegetation. White-browed Scrubwrens, at least, also eat small juicy berries (e.g. Rhagodia berries) when in abundance, which would also provide supplementary water.

Two references you might like to look up are:

Ambrose, S. J. & Bradshaw, S. D. (1988). The water and electrolyte metabolism of captive and free-ranging white-browed scrubwrens Sericornis frontalis (Acanthizidae) in arid, semi-arid and mesic environments. Aust J. Zool. 36: 29-51.

Ambrose, S. J., Bradshaw, S. D., Withers, P. C. and Murphy, D. P. (1996). Water and energy balance of captive and free-ranging Spinifexbirds (Eremiornis carteri) North (Aves:Sylviidae) on Barrow Island, Western Australia. Aust. J. Zool., 44: 107-117.

I realize that the Spinifexbird (2nd reference) is not an acanthizid, but I just wanted to demonstrate to you that other small passerines have similar strategies for maintaining body water balance.

One of the difficulties that small birds have in eating invertebrates is that their diet is also high in sodium (salt). Excess salt in the diet has to be excreted in the bird's droppings which, in turn, requires the excretion of water. The few studies that have been carried out on Australian birds show that insectivorous species that live in the arid and semi-arid zones have more efficient kidney function than those that live in the temperate zone (hence able to excrete excess sodium from their bodies in higher concentrations) and can also tolerate higher concentrations of sodium within their bodies without the need to excrete a lot of it. These adaptations help these birds to conserve body water.

Kind regards,

Stephen Ambrose
Ryde, NSW

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