Red tides are sudden increases in the numbers of naturally occurring
toxic and/or red marine algae caused by environmental factors.
I have been investigating the possibility that red tides may have
substantial effects on some seabird populations. This is of especial
concern because it appears that red tides may be increasing in
frequency and range. From my library searching, I have only been
able to compile a very short list of actual bird deaths which have
been attributed to red tides. This may be due in part to
various factors such as: low carcass deposition of birds poisoned at
sea, chance nature of red tides makes subsequent mortality an
undependable study subject, and toxicological testing can be
expensive. As a result, I am unable at this time to make any
substantive conclusions about how often red tides poison birds and
what role - if any - red tides play in regulating seabird populations
worldwide. I am enclosing my list. If anyone can refer me to other
references or can report any additional bird deaths which have
been attributed to red tides (with or without any testing) please
contact me.

Peter L. Whitlock
Raptor Research Center
Boise State University
Boise, Idaho
e-mail: whit0522 at varney.idbsu.edu

Bird Deaths Attributed to Red Tide Poisoning
When&where Bird species affected Reference
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Sep. 1991 Brown Pelicans, Brandt's Cormorants Work, et al. 1993
Monterey Bay, CA

1981 Norway Common Eider ("several thousand" killed) Bell 1989
(I need a better reference for this event)

1980 S. Africa "several dead seabirds" Horstman 1981

June 1978 Common Terns, Herring Gulls Nisbet 1983
Monomoy Is., MA

May 1978 Black Oystercatchers Hockey&Cooper 1980
S. Africa

June 1975 Shags, Herring Gulls, Fulmars, more Armstrong, et al.
Farne Is., Britain 1978

Mar. 1974 "several thousand" Lesser Scaup, others Forrester et al.
Tampa Bay, Fla. 1977

Sep. 1972 620 birds of 13 spp. + 1600 Bl. Ducks Bicknell & Walsh
Plum Is., MA 1975, also Sasner
et al. 1975
May 1968 Shags, Arctic Terns, Eiders, more Coulson et al.
Farne Is., Britain 1968

May 1942 Common Murres, Pacific Loons, more McKernan&Scheffer
Washington coast 1942