P. Pyle et al., Organochlorine concentrations, eggshell thickness, and hatchability in seabirds off central California, WATERBIRDS, 22(3), 1999, pp. 376-381
We measured eggshell thickness in seven species of seabirds breeding at Sou
theast Farallon island (SEFI) and Ano Nuevo Island, off the central Califor
nia coast, in 1993. Eggshell measurements of the Common Murre (Uria aalge)
from 1993 were significantly thicker than those of eggshells from SEFI meas
ured in the early 1970s (by 10.9%), but thinner than those of eggshells fro
m SEFI measured before 1947 (by 3.2%). In five species, eggshell thickness
measurements at SEFI in 1993 were thinner than those of eggs from Oregon co
llected in 1979 (by 0.3 to 5.8%). In four species, Brandt's Cormorant (Phal
acrocorax penicillatus), Common Murre, Pigeon Guillemot (Cepphus columba) a
nd Rhinoceros Auklet (Cerorhinca monocerata),we measured levels of six chlo
rinated hydrocarbons in the eggs and related them to eggshell thickness. Af
ter adjusting for the effects of other compounds, all six compounds had neg
ative correlations with eggshell thickness when species were pooled, althou
gh only for oxychlordane was the correlation significant. Oxychlordane also
had significant negative effects on eggshell thickness in Common Murre and
Rhinoceros Auklet, after adjusting for the effects of other compounds, alt
hough the small levels of this and the other compounds in the seabird eggs
may negate the biological meaning of these results. No other compounds (inc
luding DDE and PCB) had significant negative correlations. Hatching success
of six species at SEFI showed no significant changes during the period 197
1-1994. Based on these results wt conclude that organochlorine contaminatio
n and eggshell thinning do not currently pose a problem for seabirds off th
e central California coast.