Bond el al. • AVIAN MORTALITY AT A VOLCANO IN ALASKA 
149 
TABLE 2. Atmospheric composition of gas samples at Kiska Island, Alaska, in 2009 and 2010 (elevated CO, in the 
sample from 30 Jul 2010. indicated in bold). Data are presented as the percent composition of samples; gases representing 
<0.001% of samples are not included. Normal atmospheric composition is from NASA Global Climate Data Center. 
Gas 19 Jun 2009 4 Jut 2009 18 Jul 2009 31 May 2010 30 Jun 2010 _ 30 Jul 2010 _Air_ 
At 0.944 0.933 0.913 0.905 0.913 0.890 0.934 
0, 21.044 20.875 21.115 21.257 21.083 20.717 20.946 
N 2 77.974 78.025 77.872 77.759 77.964 77.035 78.084 
CO, 0.037 0.166 0.099 0.079 0.039 1-358_ 0.07-9 
weight of 73.0 ± 2.2 g reported in a chick growth 
study on Kiska by Major et al. (2006). 
Flattened wing chord also varied by year (/Ties 
= 33.39. P < 0.001) with corpses from 2009 and 
2010 having shorter wings than those in 2007 and 
2008 (GH, P < 0.001). The mean (± SD) wing 
chord in 2007 and 2008 was 91 ± 5 mm and 92 ± 
5 mm respectively, while in 2009 and 2010. the 
mean was 86 ± 5 mm and 85.5 ± 6 nun. There were 
1 (4%>. 3 (37c). 9 (177c). and 13 (19%) fledglings 
with w ing chords shorter than the mean wing chord 
reported by Major et al. (2006) of 80.3 ± 3.4 mm in 
2007. 2008. 2009. and 2010. respectively. 
Gas concentrations and composition were similar 
to normal atmospheric levels in all samples, except 
,or slight enrichments in CO,, which reached 
1.358% on 30 July 2010. Elevated CO, was found 
on other days, hut quantities were insufficient to 
perform isotopic analysis (Table 2). Isotopic anal¬ 
ysis of this single sample gave a 6 1 'C' of -9.55%n, 
within the range of magmatic gas from Aleutian 
Arc volcanoes (Symonds et al. 2003). A low U C 
"aluc of 0.0399 (Fraction Modern Carbon; 0.052% 
cl the total sample volume) of the July 2010 sample 
had only a trace component of biogenic CO, wilh 
’he remainder (1.306% of the total volume, or 96% 
°t (he total C0 2 ) volcanic in origin. 
DISCUSSION 
The 2009-2010 samples from the gas seep on 
Kiska Island contained only low levels of C0 2 and 
mostly auklets were found dead (Table 2). We 
^peci there is significant intcrannua! variation in 
emissions, and that emissions were higher in 2007 
and 2008 when larger numbers of small land birds 
*ere found dead (Tabic I). Dead passerine birds 
without obvious external or internal injuries, and 
no alternative explanations for numerous deaths in 
■ su ch a small area over a small temporal scale were 
lhe first indication of a possible environmental or 
geological cause of death. Toxic gas concentrations 
may only be present in lethal concentrations on 
certain days with light wind; all our sampling 
occurred when average wind speed was >25 km/hr, 
typical for the area during summer. Cold gas seeps 
that emit nearly pure CO: are known in many 
volcanic areas, such as Mammoth Mountain, 
California, where emission rates have been shown 
to vary on time scales ranging Irom diurnal to 
decadal in response to both magmatic unrest and 
meteorological forcing (Lewicki et al. 2(X)7). 
Nearly all confirmed breeding species at Sirius 
Point have been recovered in the valley containing 
the pits; exceptions being species that breed in much 
lower density in this area of Kiska Island such as 
Snow Buntings, which are uncommon local breed¬ 
ers in alpine areas of the volcano (Bond et al. 2010). 
The only vagrant found was a Brown Hawk-Owl 
(Bond and Jones 2010). 
Many dead Least Anklet fledglings were under¬ 
weight, yet few had underdeveloped wing feathers 
compared to chicks in a growth study on Kiska in 
2002 and 2003 (Major et al. 2006). This suggests 
they were in poor condition (Oyan and Anker- 
Nilsscn 1996) and were likely trapped in the valley. 
They could not fly or take off once trapped by the 
tall vegetation (mainly Puccinellio spp., Carex spp., 
and Calurnagrostis spp.), while attempting to depart 
lo the sea. We believe a combination of starvation, 
poor condition, and noxious gases contributed 
to anklet deaths. Fledgling ale ids have a natural 
inclination to descend while fledging, presumably 
an adaptation for nesting on slopes and cliffs 
(Gaston and Jones 1998). It is difficult, without 
detailed necropsies, to know it (he auklets continued 
to descend into the gas-filled depression and died 
because they could not emerge to go to sea and feed, 
or from asphyxia. In contrast, the large number of 
land birds found, and that large numbers of seabirds 
were found on only 1 or 2 days each year suggests 
that gaseous emissions had a role in avian mortality 
in some years. 
This gas seep had a weak feed of magmatic CO, 
that was only readily detectable in one of six 
