California Gulls
Gulls and
and Climate
California
ClimateChange
Change at
at Mono
Mono Lake
Lake
Justin Hite, Krisitie Nelson,
and David Winkler
• General info on
California Gulls at
Mono Lake
• Predicting future
size of the colony
• Meromixis as it
affects the colony
• Long Live Argus
monolakensis
Distribution of the California Gull
Negit Islets
Negit Island
Paoha Island
•
Paoha Islets •
Old Marina Island
•
No Islands before 2,000 bp
Negit Island primary colony
until coyotes crossed
landbridge in 1981
Now roughly 80% on Negit
Islets, 18% on Paoha Islets,
2% on Old Marina Island
Mono Lake Level 1850-Present
6440
6420
6410
6400
6392 projected average post-transition lake level (D1631)
6390
6380
6370
6360
6350
6340
18
50
18
60
18
70
18
80
18
90
19
00
19
10
19
20
19
30
19
40
19
50
19
60
19
70
19
80
19
90
20
00
Surface Elevation (feet
6430
Date
Research station and
observation blind are
both fake volcanoes
B
Brine shrimp bloom on a warm calm day
Alkali flies become more
abundant in the diet later
in the season
Long-legged flies
(Dolichopodidae)
• Not seen at Mono Lake by early Gull researchers
• First noted during 82-83 Meromixis
• Made up to 10% of gull diet from 1999-2002, and
larvae found in great abundances on sandy beaches
• The large concentrations of Long-legged flies at
Mono Lake appear to have disappeared in 2003
• Why the disappearance?
– Larvae have one of the highest salt tolerances of
Dipterans, but do other life cycles have lower salt
tolerance?
•
•
•
•
Brine Shrimp and Alkali Flies the major prey items
2000: Brine Shrimp
2001: Alkali Flies and Cicadas
2002: Brine shrimp and Alkali Flies
Diets fed to young
Broken down by sex, time
of day, time of season, and
year
•Shrimp fed most often in
morning, and at higher
proportion early in season
•Alkali fly proportion
increases during the
season, especially in 2001
and 2002
•Cicada outbreak in 2001
•Long-legged flies fed to
young in call years, and
mostly during the afternoon
Mornings typically calm,
afternoons windy, which
changes which prey types
are fed to chicks.
Number of California Gull nests in May
35000
33000
31000
29000
27000
25000
23000
21000
19000
17000
1st episode of meromixis
15000
1982
1984
1986
1988
2nd episode of meromixis
1990
1992
1994
1996
Year
1998
2000
2002
2004
2006
2008
Wrege et al 2006
4 variables predict
>80% of variability
in long-term data
1) recruits
2) winter coastal
conditions (PDO)
3) Brine shrimp
densities before
laying
4) mean temp before
laying
120
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995*
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
80
6
-2
Adult Artemia (10 m )
100
60
40
2007
20
*: Lake not sampled
in April or May 1995
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Adult Artemia Abundance
Sep
Oct
Nov
Dec
courtesy of Bob Jellison
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
190
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
1979
Day of Year of Distribution Centroid
260
250
240
230
220
210
200
y = -1.5084x + 3221.3
2
R = 0.4646
180
Adult Artemia Temporal Distribution
courtesy of Bob Jellison
35000
1.8
1.6
30000
1.4
25000
1.2
20000
1
0.8
15000
0.6
10000
0.4
5000
0
1982
0.2
0
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
Year
Number of nests
chicks fledged per nest
Nest Numbers compared to fledging rate
2006
2008
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
0
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
Year
Number of nests
estimated number of recruits
Estimated number of recruits (year t) = total number of nests (t-4) x chicks fledged per nest (t-4)
Conclusions…
• Nest numbers may increase
as spring temperatures warm
– Not known if there is an upper
temperature threshold that
would negatively affect gulls
• Nest numbers may increase
if Brine Shrimp populations
continue trend toward earlier
hatch and/or earlier “bulk”
time
What else could be
happening?
•
•
Closing of Pumice
Valley Landfill in April of
2002 to municipal
waste (a primary early
season food item for
gulls)
– Benton Crossing
Landfill still open,
and visited by
thousands of gulls
Exponential growth of
South San Francisco
Bay colony in last 10
years
Meromixis
•
•
•
•
Persistent chemical
stratification
A natural component of the
Mono Lake ecosystem with a
long history
– The lake has been
meromictic for roughly
half of the last 4,000
years
Large increase in lake level
needed to initiate meromixis,
which can then persist for
many years
Meromixis will likely continue
in the future. It will probably
occur at higher frequencies
than in pre-diversion years,
but at lower frequencies than
in last 20 years
Meromixis in the last century (from Jellison et al, 1998)
Year
Runoff (%
above avg)
1982
172% (followed
~1.8
by 193% in
1983
YES
1994
182%
1.0
YES
1938*
? (data not
recorded)
1.0
Probably not
1969*
173%
0.7
Probably not
Lake level rise
(m)
Initiated
Meromixis?
Medellin-Azuara 2008: “Required flows to
maintain Mono Lake levels were also
unattainable under the dry-warm climate
scenario.”
Breakdown of Meromixis leads to largest clutch sizes ever
reported at Mono Lake
Plot
LN
LTE
LTW
TwNor
TwS
TwW
TwNew
CC
CH
PE
PW
1E
3
7
7
4
14
6
7
4
3
5
3
2E
13
26
35
26
50
33
20
18
31
9
14
3E
4
16
46
36
36
40
24
27
22
9
15
# Nests
20
49
88
66
100
79
51
49
56
23
32
# Eggs
41
107
215
164
222
192
119
121
131
50
76
avg clutch size
2.05
2.18
2.44
2.48
2.22
2.43
2.33
2.47
2.34
2.17
2.38
Average clutch size:
2.35
Average clutch size in most years other than 2004: 1.85 eggs/nest
California Gull nests on Old Marina Island
1200
1052
Coyotes caused
100% mortality
1000
Recent history of
Gulls on Old Marina
reminds us that
Coyotes are still
perfectly willing to
invade the gull
colony
800
723
600
511
400
178
200
94
0
0
0
2001
2002
1
2003
2004
2005
Year
2006
2007
2008
Long Live Argus monolakensis
2500
3
2
1500
1.5
1000
1
500
0.5
0
1982
0
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
Year
nest numbers
chicks fledged per nest
2004
2006
2008
Chicks fledged per nest on Little Norway
2.5
2000
Acknowledgements
MLC, MBNFSA, CA State Parks, El Mono Motel,
PRBO Conservation Science, Cornell University,
and volunteers too numerous to name.
In particular: Tricia Wilson, Ann Greiner, Sacha
Heath, Bartshe Miller, Arya Degenhardt, Paul
McFarland.
For adivce on this talk: Dave Shuford, Bob
Jellison, and Scott Stine
Long Live Mono Lake!!!