POISONOUS BIRDS, GASTROLITHS

[darren.naish@port.ac.uk]

Re: gastroliths and the comments of Stephen Wroe, Steve 
Brusatte and others, it should be clear by now that 
gastroliths serve different functions in different animals and 
there is no catch-all answer to their presence. Buoyancy 
regulation, at least in part, in aquatic tetrapods; ?axial 
stability in underwater fliers; digestion in birds and other 
dinosaurs. Use of gastroliths for buoyancy control (Mike 
Taylor's contention) is being contested by Mike Everhart 
who has evidence suggesting that plesiosaur gastroliths 
were being used to mash up fish.. however, the two 
functions are not necessarily exclusive. Use of gastroliths in 
otariids is argued to augment their 'flying' style of 
locomotion and is apparently not for deep diving (IIRC the 
deepest diving pinnipeds are elephant seals, not otariids). 
More details in the papers.. see...

Cicimurri, D. J. & Everhart, M. J. 2001. An elasmosaur with 
stomach contents and gastroliths from the Pierre Shale (Late 
Cretaceous) of Kansas. _Trans. Kansas Acad. Sci._ 104, 
129-143.

Taylor, M. A. 1993. Stomach bones for feeding or 
buoyancy? The occurrence and function of gastroliths in 
marine tetrapods. _Phil. Trans. Royal Soc. London_ B 341, 
163-175.

- . 1994. Stone, bone or blubber? Buoyancy control 
strategies in aquatic tetrapods. In Maddock, L., Bone, Q. & 
Rayner, J. M. V. (eds) _Mechanics and Physiology of 
Animal Swimming_. Cambridge Univ. Press, pp. 151-161.

- . 2000. Functional significance of bone ballastin [sic] in 
the evolution of buoyancy control strategies by aquatic 
tetrapods. _Historical Biology_ 14, 15-31.

As discussed here on DML at length before, gastroliths are 
present in ant-eating taxa (including aardwolves and 
pangolins) and in insectivorous/predatory birds.. I know 
they are definitely present in hawks and thrushes but haven't 
really gotten into the literature on this yet. There is a brief 
discussion of gastrolith distribution in extant birds in the 
Cambridge University volume _Ornithology_ but I don't 
have the ref to hand.

Dann Pigdon wrote...

----------------
There's at least one species of bird from Papua New Guinea 
that is poisonous to the touch. One researcher studying birds 
in the area was scratched by a bird while removing it from a 
net, and thus discovered its toxic nature the hard way. 
----------------

The biology of pitohuis and other toxic birds is absolutely 
fascinating and proving increasingly complex what which 
Dumbacher et al's recent discovery of mimicry among the 
pitohui complex plus recognition that the enigmatic _Ifrita_ 
is also toxic. See the following for an introduction to the 
literature...

Diamond, J. 1992. Rubbish birds are poisonous. _Nature_ 
360, 19-20.

Dumbacher, J. P., Beehler, B. M., Spande, T. F., Garraffo, 
H. M. & Daly, J. W. 1992. Homobatrachotoxin in the genus 
_Pitohui_: chemical defense in birds? _Science_ 258, 799-
801.

- . & Fleischer, R. C. 2001. Phylogenetic evidence for 
colour pattern convergence in toxic pitohuis: Mullerian 
mimicry in birds? _Proc. Royal Soc. London_ B 268, 1971-
1976.

- ., Spande, T. F. & Daly, J. W. 2000. Batrachotoxin 
alkaloids from passerine birds: a second toxic bird genus 
(_Ifrita kowaldi_) from New Guinea. _Proc. Nat. Acad. 
Sci., USA_ 97, 12970-12975.

Mouritsen, K. N. & Madsen, J. 1994. Toxic birds: defence 
against predators? _Oikos_ 69, 357-358.

-- 
Darren Naish
School of Earth & Environmental Sciences
University of Portsmouth UK, PO1 3QL

email: darren.naish@port.ac.uk
tel: 023 92846045