Seabird Rete 83 



Table 1. Pattern of intercarotid anastomosis in 46 specimens of 11 species of 

 Procellariiformes. N = number examined. 







Pattern of 



Latitude of 



Species 



N 



anastomosis' 



breeding range 2 







X 



X-H H 





Fulmar us glacialis 



2 



2 





50-85° N 



Thalassoica antarctica 



1 



1 





72-76° S 



Pterodroma hasitata 



4 



4 





14-20° N 



Calonectris diomedea 



13 



13 





14-40°N 



Puffinus gravis 



4 



4 





36-40° S 



Puffinus griseus 



3 



3 





52-56° S 



Puffinus puffinus 



2 



2 





28-65° N 



Puffinus Iherminieri 



7 



7 





10-33°N 



Oceanites oceanicus 



8 



4 



3 1 



51-75° S 



Oceanodroma leucorhoa 



1 



1 





42-64° N 



Oceanodroma castro 



1 



1 





30-40° N 



'X-type is defined as having cerebral carotids anastomosing side-to-side, H- 

 type has a pronounced transverse anastomosis joining the two carotids, and 

 X-H type is intermediate with a short transverse anastomosis (after Baumel 

 and Gerchman 1968). 



2 from Palmer (1962) or Watson (1975). 



that may be exposed to thermal stress while flying across the doldrums 

 (equatorial zone with little wind). Their retes are not appreciably larger 

 than those of north or south temperate zones or Antarctic species. Birds 

 collected while they were flying at sea off North Carolina did not 

 exhibit elevated body temperatures (Platania et al., in press). The RMO 

 of the Black-capped Petrel, Pterodroma hasitata, a tropical species, is 

 not different from that of other species of higher latitudes. The bird is 

 not subjected to heat stress at its nesting grounds because it is a winter 

 (Northern Hemisphere) breeder, and because at high elevations it exca- 

 vates burrows. Altitude, and the extent of the use of burrows for nest- 

 ing, further cloud simple correlations of RMO ratios with latitude. In 

 general, the smaller birds nest exclusively in burrows or crevices while 

 the larger shearwaters and fulmars are open ground or cliff nesters. In 

 addition, most ground-level activity of burrowing species occurs at 

 night, further reducing heat stress. 



As arterial blood may reach the brain via several routes (Richards 

 and Sykes 1967; Richards 1970; Crowe and Crowe 1979), involving both 

 direct and indirect (via extensive anastomoses) flow, the potential exists 

 for selectively regulating flow under varying conditions. Flow of arterial 

 blood may be shunted through the RMO to the brain via anterior anas- 

 tomoses with intracranial branches of the internal carotid. This could 



