chick hatching is accentuated at fledging. In 1995, cliff-top fledging did not begin until
after the final research trip of the season, while crevice fledging was nearly complete
(Figure 5).

Delays in phenology may also be the result of laying opportunities. Data from the time-
lapse camera indicate that while cliff-top nesters (as exemplified by the MCT) and crevice
nesters (as exemplified by CC1-5, TC1-4) are present on their respective breeding areas an
equal portion of the day early in the season, crevice nesters begin to occupy the nesting area
full time by mid-June while cliff-top nesters do not (Table 4). In 1995, murres on the
MCT were visible on the cliff 100% of the visible hours on only 2 out of 31 monitored
days after mid-June. On 13 of those days, murres were completely absent from the
subcolony. Annual comparisons indicate that later in the season when murres should be
attending full-time (that is, assuming they have chicks), crevice-nesting murres always
spend more time on their breeding areas than cliff-top nesters (Figure 6). In 1994,
attendance patterns appeared more similar between habitat types (that is, cliff-top nesters
were present more often); however, this appears to be the exception rather than the rule.

_ Reproductive Success

In 1995 monitored crevice subcolonies (CC1-4) had the highest reproductive success
_ Tecorded during the 1992-1995 interval (Table 5). With the exception of CC2,
reproductive success was equal to or greater than 0.85 chicks per pair. CC2 would.
probably have experienced higher reproductive success as well; however, early in the
season, (18 June 1995) a juvenile Bald Eagle landed on CC2, causing the destruction of 12
eggs (as a result of breakage as well as predation by gulls once the eagle had left). It is not
known whether this incident was repeated but Olympic Coast National Marine Sanctuary
personnel reported sighting an eagle remove a murre from the CC subcolonies during mid-
July (E. Bowlby, pers. comm.).

Reproduction on the cliff-top subcolonies was lower than in the crevices. The MCT failed
to hatch any eggs. This subcolony has now failed 4 out of the last 6 years. TPCT] failed
to hatch any eggs. Pole Island probably fledged chicks, although no visits were made to
this subcolony in 1995. However, a small number of chicks (10-12) were seen on the Pole
Island subplot counting area during mid-late August. Petrified and TPCT2 had 1-2 week-
old chicks during the last research trip of the season (22-24 August 1995); barring an

unknown disaster, these chicks probably fledged. Adults were seen bringing fish back to
Pole Island and Petrified.

16


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Introduction

In July of 1991, the sinking of the Tenyo Maru released an estimated 100,000 gallons of
oil into the waters immediately north of Tatoosh Island. At the time of the spill, over 4,000
Common Murres, Uria aalge, were nesting on the island, in addition to four other species
of alcids, two species of cormorants, two species of storm-petrels, and one species of gull

(Glaucous-winged Gulls, Larus glaucescens). Tatoosh Island (48° 24' N, 124° 44' W),
is actually a collection of rocky islets connected by boulder and cobble beaches at low tide.
There are five main islets, three of which - North Island (Rock #022), Pole Island (Rock
#023), and Main Island (Rock #021) - have vertical cliff faces with ledge or crevice habitat
suitable for murre nesting. Oil began to wash past Tatoosh Island on 26 July 1991,
covering patches of intertidal on the western and northem parts of the island (Parrish pers.
obs.). During the next three days (while researchers were present on the island), 70
severely oiled Common Murres were observed swimming to shore and beaching
themselves around the island (R. Paine unpub. data). In total, 3,157 murres were
recovered from a number of locations along the Washington coast during the spill, the
majority of these were carcasses.

Attempts to determine whether the spill resulted in injury to the Tatoosh Island murre
colony were hampered by a lack of specific data on reproductive success of the colony in
years prior to the spill, as well as several confounding factors following the spill. Chief
among these were a persistent El Nifio-Southern Oscillation (ENSO) event in the years
following the spill (1992-1993), and an escalating interaction between murres and their
chief predators: Bald Eagles, Haliaeetus leucocephalus (on adults), and Glaucous-winged
” Gulls (on eggs). Despite these problems, colony monitoring in the years following the
spill revealed several patterns: : . .
1, Island-wide attendance declined following the spill (1991 to 1993), but began to rise
again in 1994.
2. The colony is divided into many subcolonies which can be loosely grouped by habitat
type into: cliff-top (5-6 subcolonies) and crevice (>25 subcolonies). Cliff-top subcolonies
are, on average, orders of magnitude larger than crevice subcolonies, and house a
disproportionately large percentage of the Tatoosh Island population (75-80%).
3. Reproductive success of monitored subcolonies was lowest in 1993 and also rebounded
in 1994.
4. Murres nesting in cliff-top subcolonies experienced lower reproductive success than
conspecifics nesting in crevice subcolonies in all specifically monitored years. Some cliff-
top subcolonies experienced total breeding failures.


Hudson, P. J. 1985. Population parameters for Atlantic Alcidae. In: The Atlantic Alcidae.
D.N. Nettleship & T. R. Birkhead (eds.) Academic Press, New York. pp:233-
261.
Parrish, J. 1995a. Status of the Common Murre, Uria aalge, population on Tatoosh Island,
Washington, Final Report ( 1992-1994), unpublished report to the U. S. Fish &
Wildl. Serv.
Parrish, J. K..1995b. Influence of group size and habitat type on reproductive success in
common murres (Uria aalge). Auk 112:390-401.
Parrish, J. K. Coincident communication: heterospecific use of alarm signals.
: (manuscript)
Parrish, J. K. and Paine, R. T. 1996. Ecological interactions and habitat modification in
nesting Common Munes, Uria aalge. Bird Conservation International in press.
Parrish. J. K. and Paine, R. T. Conservation conflicts-of-interest: A case study of
Common Munes and Bald Eagles. Ecological Applications (submitted).
Wilson, U. 1995. Washington Common Murre colony surveys 1995. Unpublished report
to the Tenyo Maru Trustee’s Council. November 1995.

31


Table 4 -Percent of visible hours attended by Common Murres on the Crisscross subcolonies (CC1-5;

RCC, FRCC) and the MCT as assessed by the timelapse camera, Tatoosh Island, 1993-1995. Blanks are
no pictures taken.

1993 1994 1995
Vis. Hrs CREV %.MCT %| Vis. Hrs CREV & MCT %| Vis. Hts CREV % MCT %
16-May 9 22 0
17-May : 13 23 23
18-May 14 0 0
19-May 14 14 14
20-May 14 21 21
21-May 13 0 0
22-May 13 0 0
23-May . 14 0 0
24-May 14 7 0
25-May 6
26-May 15 40 33
27-May - 14 71 43
28-May 8 63 63
29-May 13 100 31
30-May 14 36 14
31-May 9 55 33
1-Jun 11 36 27
2-Jun 15 80 53
3-Jun 12 50 17
4-Jun 12 17 33
5-Jun 13 30 8
6-Jun 12 25 25
7-Jun 1] 63 27
8-Jun 13 76 62
9-Jun 14 86 50
10-Jun 14 86 43
-11-Jun . : 8 100 25
12-Jun ll 100 36
13-Jun 10 90 40
14-Jun ll 100 55
15-Jun
16-Jun
17-Jun 8 100 100
18-Jun 13 100 71
19-Jun - 14 93 64
20-Jun 9 100 100
21-Jun 10 100 70
22-Jun : 10 100 80
23-Jun 14 100 43
24-Jun 14 100 21
25-Jun : 12 100 42



Table 6 - Common Murre eggs lost from/found on a variety of locations around Tatoosh
Island, 1994-1995.

on under under on Other Total
MCT MCT TP/TPC Island
T *. top
1994 (#) 178 12 19 44 25 278
(%) 64 4 7 16 9.
1995 (#) 77 19 11 40 27 174
(%) 44 11 - 6 23 16

Table 7 - Disturbance factors causing Common Murres nesting on the MCT subcolony on

Tatoosh Island to partially or totally evacuate, 1992-1995. These totals exclude researcher
disturbance (see Table 9). Unk=unknown.

Partial Total
Unk Eagle = NotEagle Unk Eagle Not Eagle

1992 3 30° 2 1 13 0
1993 0 5 4 0 1 0
1994 8 26 10 0 7 4
1995 2 1 5 0 8 0
Total 15 35 21 1 29 4
% excluding

unknowns 62 38 88 12

Table 8 - Total amount of observed time (in minutes) MCT Common Murres spent on and
off the subcolony as a function of known disturbance. Data are from 16-19 and 25-27
June 1995.

Empty Partial Full Total
Eagles . +s 343. 60 - 403
Sound Experiment 5 10 - 15
Aircraft 0 15 - 15
Unknown 140 460 - 600
: - 82 82
Total [488 345 82 . 115

Table 9 - Witnessed attacks and kills by Bald Eagles on/of Common Murres on Tatoosh
Island, 1991-1995.
1991 1992-1993 1994 1995

Attacks 5 5 1 5 4
Kills : 1 1 0 5 2
Bodies found* 12 12 4. 20 19
Observation hrs 60 “80 46 90 5S

* includes witnessed kills



Table 4 -Percent of visible hours attended by Common Murres on the Crisscross subcolonies (CC1-5;

RCC, FRCC) and the MCT as assessed by the timelapse camera, Tatoosh Island, 1993-1995. Blanks are
no pictures taken.

8-Aug 13 100 23

9-Aug 12 100 0 ret 100 0
10-Aug 13 100 0 0
1l-Aug = 12 100 0 11 100 0
12-Aug 12 100 8 12 100 8
13-Aug 13 100 0 12 92 0
14-Aug 8 100 0 10 50 0
15-Aug 11 100 0
16-Aug . 11 100 0
17-Aug ~ 12 67 0
18-Aug 0
19-Aug 13 92 0



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discrepancy in attendance as a function of habitat type. A separate table presents data on
the amount of time per day subcolonies were occupied.

Reproduction

Reproductive success was estimated as the number of fledglings per pair for four crevice
subcolonies (CC1-4) where pairs could be mapped and the fate of eggs/chicks could be
followed. Chicks were defined as fledglings and likely fledgers (i.e. healthy chicks greater
than 15 days of age). The fate of mapped chicks was followed through fledging when
possible. The number of pairs is reported as a minimum because staggered visits
compromised an accurate assessment of egg loss, number of pairs re-laying, and/or
number of pairs abandoning for the season. For other subcolonies, Teproductive success
was noted (e.g. produced eggs, chicks, or fledglings) if possible.

Eagles

Data on eagles comes from a variety of sources in addition to that collected by the principal
investigator. L’ata on the number of active eagle territories (defined as those territories with
nests that produce at least eggs) within 25 km of Tatoosh is collected by the Washington
Department of Fisheries and Wildlife (WDFW) and provided by the WDFW non-game data
base manager, Tom Owens. The maximum number of eagles seen simultaneously on
Tatoosh per research trip during the murre breeding season is collected and provided by Dr.
Robert T. Paine. In addition, data are collected on the number of attacks and kills made by
eagles on murres, as well as the number of murte carcasses thought to have been the victim
of eagles. Finally, the number of witnessed temporary evacuations by murres nesting in
the MCT subcolony are counted dnd ascribed toa specific disturbance, when possible.

Results

Attendance .

In 1995, the number of murres attending Tatoosh Island dropped below 1994 levels by
almost 12% (Figure 2; Table 1). This drop appears to have been driven by significant
declines in cliff-top subcolony attendance. Cliff-top attendance dropped 30% from 2757 in
1994 to a 5-year record low of 1915 in 1995 (Table 1). On the MCT, attendance was cut in
half from 1200 iri 1994 to 600 in 1995. There were also declinés in the Pole Island subplot
(down 12%) and the Petrified subcolony (down 33%; Table 1). The drop in cliff-top
attendance was offset, to some degree, by an inverse trend in the crevice subcolonies.
Fifteen of the 25 crevice subcolonies in existence in 1994 increased in size and 6 new
crevice subcolonies were born (Table 1). This brought crevice subcolony attendance to a


leading to the highest crevice subcolony attendance on record: 1355 or 41% of total
attendance. Furthermore, fledging occurred in at least one of these new subcolonies
(Rainbow Rock - upper; RR-U). It seems likely that Tatoosh murres may have been
switching breeding areas within the colony, although without banded individuals this
conclusion is only based on correlative evidence. In any event, the pattems of attendance
and reproduction in 1995 indicate that murres may be more flexible than a highly
philopatric behavioral model would suggest (see also Halley & Harris 1993).

Behavioral flexibility may be a response to continued, perhaps escalating, direct and
indirect pressure by Bald Eagles. With eagle visits, attacks, and captures rising, murres
would at least continue to experience widespread reproductive failure and even loss of life,
if the distribution between habitats remained predominantly cliff-top nesters. Simple life
table models indicate that the Tatoosh colony could be substantially reduced in size by
continued eagle pressure. It is too early to say whether the apparent movement towards
crevice colonization will allow the Tatoosh Island population to circumvent the indirect
effects of eagles. As eagles landed on at least one crevice for the first time this year, the
movement by murres towards crevices may not be sufficient to ensure adequate survival
and reproduction.

The incidence of eagle-induced disturbance of murre colonies does not appear limited to
Tatoosh Island. Early in the murre nesting season, juvenile Bald Eagles apparently
prevented breeding area colonization on Oregon’s largest murre colony - Three Arch Rocks
(Lowe pers. comm.). On Triangle Island, the largest stable Common Murre breeding
colony in British Columbia and the nearest large colony north of Tatoosh, Bald Eagles
exert a serious direct effect (predation on adults) as well as indirect effect (eagle -facilitated
egg predation; Parrish pers. obs.). In addition, on this colony Glaucous-winged Gulls
appear to be much more aggressive, stealing eggs and even chicks from attended
subcolonies (J. Salatas pers. obs.). Comparisons between murre colonies might help
indicate those factors which are regionally, versus locally, important in determining the
survivorship and reproductive success necessary to produce “source” rather than “sink”
colonies.

Attempts to elucidate the behavioral interactions between eagles, murres, and egg predators
have proved fruitful. Parrish (1995b) has documented the effect eagle overflights have on
murre behavior as a function of nesting habitat (i.e. crevice versus cliff-top). Parrish and
Paine (1996) showed that temporary habitat manipulations on a cliff-top subcolony (MCT)

29



only 7% of the time (Table 8). Almost 44% of the time, the subcolony was empty. During
these visits a minimum of 37 temporarily abandoned eggs were stolen by gulls and crows.
It is important to determine which disturbance factors are primarily responsible, especially
as experiments were conducted during these visits which resulted in temporary
abandonment. Of 488 minutes in which the MCT was empty, 70% were the direct result of
eagle overflights. Researcher experiments resulted in a total of 5 minutes (1% of total) of
abandonment. In total, researcher experiments caused the murres to partially or totally
evacuate for 15 minutes (1% of the total observation time) and resettlement, defined as the
time elasped until the murres resumed their original positions and behavior, was ;

approximately one hour in total. Aircraft caused a similar amount of disturbance, although
never total abandonment.

Although eagles appear to influence murre demography on Tatoosh primarily through their
facilitation of gull and crow egg predation, they also prey on adult murres. In all years
(1991-1995), eagles were witnessed attacking murres. In 1994 and 1995, the success rate
and the body count are higher than previous years (Table 9) perhaps indicating that the
direct effect exerted by eagles is rising. In 1995, a juvenile eagle was successful in
capturing a murre for the first time (as a function of all witnessed events), and eagles were
witnessed landing in crevice subcolonies for the first time (see above - Reproduction; Table
5). Over the long term, eagle numbers in the vicinity of Tatoosh are increasing. The
number of active Bald Eagle territories (defined as nests with offspring) within 25 km of
Tatoosh is close to 20 (Figure 7; Data from WDFW) and the maximum number of eagles
seen simultaneously per research trip to Tatoosh has also steadily increased (Figure 8; data
” from Dr. Robert T. Paine). °

The influence of eagles on the Tatoosh Island Common Murre colony is difficult to predict
accurately; however, using general assumptions about the distribution of murres on the
island and standard murre life history parameters from other banded colonies, a life table
can be constructed illustrating the relative impact of direct (i.e. predation on adults) versus
indirect (i.e. egg predator facilitation) effects (Tables 10 and 11). Four age-specific
parameters (in the absence of eagles) were estimated using information from banded
Common and Thick-billed Murre colonies: percent surviving, percent of those returning to
the breeding colony, percent of those attempting to breed, and reproductive success (data
from Boekelheide et. al. 1990, Gaston et. al. 1994, Hedgren 1980, Hudson 1985). A
stable age distribution was constructed with murres were aged 0 to 31. The rate of
population increase was set at 0.8% annually (lambda = 1.008; Table 11) to account for

26


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5. Cliff-top subcolony failures are apparently the result of disturbance by eagles, causing
adult murres to temporarily abandon their breeding areas. During evacuation periods, gulls
are able to remove undefended murre eggs. In years of subcolony failure, no eggs last
long enough to hatch into chicks. In cliff-top subcolonies which do produce
chicks/fledglings, the timing of reproduction (phenology) is one-two weeks later than
adjacent crevice subcolonies.

In 1995, Common Murre attendance, phenology, and reproductive success was monitored.
In addition, interactions between murres, eagles, and gulls were examined in a continuing

effort to predict the degree to which the murre population on Tatoosh Island may be
negatively affected. This report documents the data collected during the 1995 field season
and provides an analysis of the patterns of murre demography relative to previous years.

Methods

Data documenting murre attendance, phenology, and breeding success by subcolony, were
collected on Tatoosh Island during the April-September period. Research trips spanned 3-5
days. All data were collected from remote observation sites with the aid of binoculars, a
spotting scope, and a remote 35 mm camera. The majority of the behavioral data were
collected from a single location which afforded a simultaneous view of eleven separate
subcolonies, operationally defined as a group of nesting murres, spatially separate from
any other group (Burning Barrel Point, BBPT). From this location, observations were
made in 1/2 hr. blocks, evenly spaced over each trip, starting at 0500H and ending at
2200H (approximately 55 hrs in total). Additional attendance data were collected from

“ several locations around ‘he island which afforded unimpeded views of various

subcolonies. Early in the season, before the murres had colonized the Island (April),
estimates were made of the cumulative number of murres attending three rafts traditionally
located just offshore of the three largest cliff-top subcolonies (MCT, Pole Island,
Petrified). These data were collected by Dr. Robert T. Paine. Annual raft counts were
used as an additional index of population size.

Attendance

Subcolony attendance was assessed at Icast once during every trip, and several times for
those subcolonies visually accessible by land. Attendance was defined as the number of
murres on the subcolony (direct count), after eggs had been laid but before chicks had
started to fledge. Attendance counts were limited to after 1200H and before dusk
(approximately 2000H), when accurate counting became more difficult. Earlier counts


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Phenology

‘The timing of murre reproduction on Tatoosh Island was divided into several periods: Egg
- when eggs only are present; Chick - when eggs begin to hatch but no fledging has
occurred; and Fledging - when chicks begin to fledge. Because subcolonies did not always
begin periods synchronously, but did tend to synchronize within habitat type (i.e. cliff-top
versus crevice), phenology is reported by habitat type. During each visit to the island, the
presence of eggs and chicks were noted daily for all visible colonies. Later in the season,
nightly checks were made for the presence of fledglings, which are difficult to see but can
easily be heard calling. Phenology is presented as a combination of these observations plus

inference about likely onset times of each period based on an average egg residence time of
30 days and a minimum chick residence time of 15 days.

To determine daily attendance pattems as a function of subcolony habitat type (crevice
versus cliff-top), a remote time-lapse 35 mm Nikon F3 camera with a 28mm lens, a 250
frame back, and a motor drive was installed on Strawberry Island (Rock #035). The
camera faced east, photographing the crevice subcolonies from Lighthouse 4 (LH4) to TC4
and included the cliff-top subcolony MCT. Pictures were taken every hour from 0600H to
2000H, until all frames had been used. An intervalometer was used to set the frame rate
(one frame per hour) and a modified garden hose timer was used to tum the intervalometer
_ on and off so that no pictures were taken at night.- Film used was Fugi Professional 100

ASA bulk film. All equipment was housed in a water tight Pelican box with a clear

Plexiglas window through which the camera was focused. The Plexiglas was protected by

a metal shade to minimize rain streaking, bird guano, and glare. The camera was reset with
“ new film and batteries four times throughout the season.

Usable frames provided general information about when subcolonies were occupied. For
each day, the total number of visible hours (defined as slides in which murre presence can
be detected on the subcolonies), the number of hours murres are present on the crevices,
and the number of hours murres are present on the clifftop are summed. Only days in
which the total number of visible hours equaled or exceeded 7 were used. From these data,
the percent of total time each habitat was occupied (per day) was calculated. The difference
between these two values is relative presence, in percent. For example, if there were 9
visible hours, the crevices were occupied 5 hours and the clifftop 3 hours, percent time
occupied would be crevice = 55% and clifftop = 33%. Relative presence would be 22%
towards the crevice subcolonies. Relative presence is graphed by day, where the x-axis is
positive from 0 to 100% in both directions. Thus, this index indicates whether there was a



Table 5 - Tatoosh Island Common Murre reproductive output in monitored crevice
subcolonies (1992-1995). Known pairs are defined as all pairs (assessed by location)
which did or were suspected to have eggs. Known lost eggs were either observed
abandoned, stolen, smashed, or failing to hatch. Because researchers were not
continuously present on the Island, known pairs and known lost eggs are minimum
estimates of pairs and lost eggs, respectively.

1992 1993 1994 1995

ccl
Attendance (aft) 31 28 29 38
Known Pairs 15 ll 22 18 :
Known Lost Eggs 2 1 1 1
Chicks > 15D ll 7 20 17
Chicks/Pair 0.73 0.64 0.91 0.94
Chicks/Attendance 0.35 0.25 0.69 0.45
cc2
Attendance (aft) 36 30.35 54
Known Pairs 17 9 21 15
Known Lost Eggs 2 4 2 12
Chicks > 15D 16 2 18 11
Chicks/Pair 0.94 0.22 0.86 0.73
Chicks/Attendance 0.44 0.07 0.51 0.20
CcCc3
Attendance (aft) 30 17 27 57
Known Pairs 11 2 7 20
Known Lost Eggs 0 2 6 3
Chicks > 15D 7 0 1 17
Chicks/Pair 0.64 0.0 0.14 0.85
Chicks/Attendance 0.23 0.0 0.04 0.30
“cc4 .
Attendance (aft) 13 17 21
Known Pairs 6 7 7
Known Lost Eggs 1 0 0
Chicks > 15D 3 6 7
Chicks/Pair 0.50 0.86 1.00
Chicks/Attendance 0.23 0.35 0.33


Continued Monitoring of Common Murres on Tatoosh Island

Final Report 1995
September 1996

Julia K. Parrish
Zoology Department, Box 351800
University of Washington
Seattle, WA 98195

‘ jparrish @u.washington.edu
prepared for the Tenyo Maru Trustee’s Council
Principal Investigator: Julia K. Parrish
Makah Tribal contacts: Dan Greene

. Denise Dailey
Makah Student Intern: Neuee Vitalis
Technician: Karen Jensen
Hourly Employees: Johanna Salatas

Trista Patterson


‘Table ‘| Average estimated annual attendance (afternoon counts during the egg/chick period) - Tatoosh
Island Common Murres.

Subcolony Rock# Habitat 1991 1992 1993 1994 1995 Comments

a |rainbowrock-u 035 crevice : 212 |bom in 1995
a |rainbow rock - 1 035 crevice 50 63 24 35 38
a |boom 021 clifftop | 50 0 0 0 0 |died in 1991
m |north island 022 crevice 99 134-100 150 136
m |northisland ridge 022  clifftop 22 0 {bor in 1993
m |north island 2 022 crevice 27 {born in 1995
m |finger 022 crevice : 31 16 |borm in 1994
m |pole island 023 clifftop | 1300 1532 1176 1264 1108 |plot est. @ 25%
m |lighthouse 1 021 crevice 89 75 27 101 110 :
m |lighthouse 2 021 crevice 3 0 1 8 6
m |lighthouse 3 021 crevice 23 15 0 25 19
m |lighthouse 4 021 crevice ll 25 8 6 - 28
m |lighthouse 5 021 crevice 17 }bom in 1995
m |submarine 021 crevice 50 30 42 43 44
m {burning barrel 021 crevice 6 9 0 6 2
m |burning barrel 2 021 crevice 32 |bor in 1995
m |burning barrel 3 021 crevice . 2 |borm in 1995
m |above crisscross 021 crevice 3 6  |bom in 1994
a {crisscross 1 021 crevice 39 32 28 29 38
a |crisscross 2 021 crevice | 45 37 30 36 54
a |crisscross 3 021 crevice 27 31 17 27 57
a/m\crisscross 4 021 crevice | 60 35 34 52 50
a/m\crisscross 5 021 crevice | 173 94 85 104 141
m |r-crisscross 021 crevice 15 21 10 26 36
m |fr-crisscross 021 crevice 20 19 12. 22 12
a |tenniscourt 1 021 crevice 79 36 30 29 40
a |tenniscourt-2° 021 ~* crevice 50 29 23 20 26.
a |tenniscourt 3 021 crevice 82 91 71 64 71
a |tenniscourt 4 021 crevice | 25 23 yal 21 19
m |moustache 021 crevice 3 {born in 1995
a |toadpoint 1 021 crevice | 50 27 25 43 60
a |toadpoint 2 021 crevice 50 22 35 24 24
a |toadpoint 3 021 crevice 50 15 15 19 23
a |tpclifftop 1 021 clifftop | 48 30 26 7 15 |partial count
a |tpclifftop 2 021 clifftop 24 46 30 4 17 |partial count
a |main clifftop 021 clifftop | 1500 1200 1300 1200 600 |max count
a |below met 021 crevice 10 0 |born in 1994
a_|petrified 021 clifftop | 200 200 200 260 175_|visit est. -
total 4214 3871 3370 «3691 = 3270
mom-aft multiplier 1.6 1.5 1.2 1.3 1.13
crev total 1092 863 ©0638 «= 934. «1355
ct total 3122 3008 2732 2757 1915

crevice % 26 22 19 25 4l


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growth patterns on Tatoosh experienced during the 1980's. Tatoosh Island parameters,
specifically total attendance in 1995, estimated eagle predation, and reductions in
reproductive success as a function of habitat type (crevice versus cliff-top) estimated over
the 1991-1995 period were substituted into the model. Thus, eagle effects did not affect
either returns at age or breeding at age. Island attendance (3270) was multiplied by 1.67
(Harris 1989) to estimate the on-colony population (approximately 5400). This total was
multiplied by age-specific on-colony percentages to estimate the number of murres at age
on Tatoosh. These figures were then used to back calculate the total number of murres
(that is, on-colony plus non-breeding pool) in the Tatoosh population. The model was then
run with this initial, stable age distribution, where survivorship and reproductive success of
on-colony birds was systematically adjusted to mimic estimated eagle effects. Population
growth rate (lambda), population size after 100 years, and the number of years to extinction
(defined as population size < 100) were calculated iteratively as a function of habitat type.

Both direct and indirect eagle effects cause the population to decline (Table 11). Eagle
Prec xtion at 2% of the on-colony cliff-top population will cause extinction in 599 years,
whereas the cliff-top population will extinct itself in only 70 years if the influence of eagle-
facilitated egg predation is included. In this simple model, the ratio of murres nesting in
crevices versus cliff-tops was kept constant, even though this ratio would likely change if
birds in one habitat were differentially affected, as was the case on Tatoosh in 1995,
Nevertheless, as a broad comparative too! this simulation underscores the importance of
indirect effects in regulating the Tatoosh murre population.

* Discussion

Itis clear from the 1995 season on Tatoosh Island that Common Murre demographics are
difficult, if not impossible, to accurately predict from previous years. Although the murres
appeared to be in “recovery” from the combined effects of the Tenyo Marv oil spill and the
1992-93 ENSO event in 1994, 1995 saw a drop in whole-island attendance combined with
extremely high reproductive success in the monitored crevice subcolonies. The drop in
attendance is therefore probably not the result of nearshore oceanographic changes in food
supply. There are no known (to the author) seabird mortality events which would have
caused such an attendance decline. Furthermore, Common Murre censuses along coastal _
Washington and Oregon were the highest recorded since 1988 (Mahaffy pers. comm. of
data collected by U. Wilson and R. Lowe). Finally, the 1995 drop in Tatoosh Island
attendance was accompanied by a dramatic switch in the pattern of island colonization.
Murres joined crevice subcolonies and 6 new crevice subcolonies were born, both factors

28



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were smaller (Figure 1), probably due to a larger percentage of foraging birds earlier in the
moming. Because several subcolonies could only be counted in the morning due to tidal
constraints, a morning to afternoon correction factor has been calculated for each monitored
year (see Table 1) and applied to the moming-only subcolonies such that a total afternoon
attendance figure could be reported. Therefore, unless otherwise stated, attendance is
reported as afternoon figures. :

For small subcolonies (e.g. <200 birds attending) direct counts were always made.
Occasionally, a subcolony could not be counted from a single location (e.g. Crisscross 4
and 5, CC4-5). In these cases, repeated counts were made from all possible venues in
order to estimate a correction factor for out-of-sight birds when counting from the BBPT
location. This difference is reflected in direct count totals from the BBPT location (ie.
Table 2) and the overall island attendance estimates (i.e. Table 1). For larger subcolonies
attendance was estimated by counting a subplot, usually not less than 20% of the total, and
extrapolating total attendance by estimating the area of the subplot relative to the area of the
ertire subcolony (e.g. Pole Island). On occasion, a direct count of large subcolony
attendance was made when the murres resettled after rafting on the water (e.g. MCT).

Because this method may underestimate attendance, annual maximum values are Teported

rather than seasonal averages. Several subcolonies were not visually accessible, or only
partially so. In these cases, attendance was estimated by measuring the areal extent of the
subcolony and extrapolating attendance using density figures obtained from subcolonies
with similar topography (e.g. Petrified). In two cliff-top subcolonies (Toad Point Cliff-top
1 and 2, TPCT1-2), only visible birds lining the cliff's edge were counted directly from a

“ location beneath the cliff, even though more murres, at least 100 on TPCT! were definitely

nesting there.

Island-wide attendance is presented as an amalgam of these methods; thus this figure does
not have confidence intervals and is meant as a gross indicator of population size,
comparable with Tatoosh attendance estimates collected in previous years. More
statistically valid attendance counts were made of 9 crevice subcolonies (CC1-5; TC1-4) by
repeatedly counting murres throughout the nesting season. For these subcolonies, data are
constrained by time of day (morning versus afternoon) and phenology (during egg and

chick period only), and presented in both graphic and tabular form as mean and standard
deviation.


Table 4 -Percent of visible hours attended by Common Murres on the Crisscross subcolonies (CC1-5;

RCC, FRCC) and the MCT as assessed by the timelapse camera, Tatoosh Island, 1993-1995. Blanks are
no pictures taken.

26-Jun
27-Jun 8 100 63
28-Jun 13 100 38
29-Jun 13 85 69
30-Jun 10 100 40
1-Jul 15. 100 27
2-Jul a 13 100 31
3-Jul 10 100 0
4Jul 10 100 10
5-Jul 14 100 0
6-Jul 14 100 0
7-Jul 12 100 8
8-Jul 12 100 8
9-Jul 12 “100 0
10-Jul 6
11-Jul 8  . 100 88
12-Jul ll 100 72
13-Jul 11 100 82
14-Jul . 6
15-Jul 9 100 22
16-Jul 11 91 55
17-Jul 1
18-Jul 4
19-Jul 13 100 46
20-Jul ll 100 36
21-Jul 2 .
22-Jul ll 100 55
23-Jul 5
- 24-Jul oe - 7 100 86
25-Jul ll 100 82
26-Jul _
27-Jul
28-Jul 7 100 71
29-Jul 13 85 85
30-Jul 9 100 89
31-Jul 13 92 46
1-Aug 13 100 33
2-Aug 7 100 29 2
3-Aug = 13 100 38 11 100 91
4-Aug 14 100 719 10 100 100
5-Aug. 12 100 42 13 100 100
6-Aug 9 100 44 12 100 92
7-Aug 14 100 14 10 100 100


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List of Figures and Tables

Figure 1. Diurnal pattern of attendance of Tatoosh Island Common Murres, 1995.

Figure 2. Annual attendance of Tatoosh Island Common Murres, 1995.

Figure 3. Distribution of attending Tatoosh Island Common Murres by subcolony size and
habitat type, 1995.

Figure 4. Annual attendance of Tatoosh Island Common Murres on nine multiply-censused
crevice subcolonies, 1991-1995.

Figure 5. Approximate phenology of Tatoosh Island Common Murres, 1995.

Figure 6. The relative presence of Tatoosh Island Common Murre crevice subcolonies as
compared to cliff-top subcolonies, 1993-1995.

Figure 7. Active Bald Eagle territories within 25 km of Tatoosh Island, 1971-1994.
Figure 8. Average annual maximum Bald Eagle sightings on Tatoosh Island, 1981-1995.
Table 1. Average annual attendance of Tatoosh Island Common Murres, 1991-1995.
Table 2. Average annual attendance counts from BBPT of Tatoosh Island Common Murre
crevice subcolonies, 1991-1995, :

Table 3. Comparison of aerial versus land-based attendance estimates of Tatoosh Island
Common Murtes, 1995. ;

Table 4. Comparison of crevice and clif-top subcolony Tatoosh Island Common Murre
daily attendance patterns, 1993-1995. . .

Table 5. Reproductive output of Tatoosh Island Common Murres nesting in multiply-
censused crevice subcolonies as a function of time.of day, 1992-1995.

Table 6. Tatoosh Island Common Murre egg loss, 1994-1995.

Table 7. Disturbance factors causing Tatoosh Island Common Murre temporary
abandonment of the MCT subcolony, 1992-1995. :

Table 8. Amount of time Tatoosh Island Common Murre nesting on the MCT spent off the
subcolony as a function of known disturbance source, 1995.

Table 9. Witnessed attack and kills by Bald Eagles of Tatoosh Island Common Murres,
1991-1995.

Table 10. Life table parameters used to model extinction time of Tatoosh Island Common
Mure population as a function of Bald Eagle direct and indirect effects.

Table 11. Results of the life table model used to model extinction time of Tatoosh Island
Common Murre population as a function of Bald Eagle direct and indirect effects.

iv


Table 2 - Average attendance counts from BBPT (1991-1995) during egg/chick period for monitored
crevice subcolonies.

Note that counts for CC4 and CCS are lower than in Table 1 because neither crevice
was entirely visible from BBPT.

Mornay MornSD MornN Aft av Aft SD AftN

1991 crisscross 1 24.50 8.67 3 38.50 16.26 2
crisscross 2 16.83 4.54 3 44,83 28.06 3
crisscross 3 27.00 1
crisscross 4 42.00 19.67 3 59.75 14.50 2
crisscross 5 110.00 8.66 3 173.33 66.82 3
tenniscourt 1 30.00 1 78.50 30.41 2
tenniscourt 2 30.00 1 50.00 1
tenniscourt 3 60.00 1 _ 81.50 26.16 2
tenniscourt 4 10.00 1 25.00 7.07 2
TOTAL 323.33 578.42

ADJUSTED 291.73 505.21

Note: The 1991 counts were made from SB and TP NOT BBPT: pre-spll only
Adjusted totals: BBPTCC4=CC4*.5; BBPTCC5=CC5*.75; AFT=MORN*1.6

1992 crisscross 1 21.20 9.36 5 31.25 5.73 8
crisscross 2 25.20 7.46 5 36.00 9.74 8
crisscross 3 15.80 9.36 5 30.25 6.86 8
crisscross 4 10.60 3.13 5 15.88 1.81 8
crisscross 5 76.40 22.81 5 93.88 18.14 8
tenniscourt!  26.40° 12.10 5 34.88 3.40 8
tenniscourt 2 19.60 10.24 5 27.50 3.42 8
tenniscourt 3 66.40 34.26 5 90.88 10.26 8
tenniscourt 4 17.00 7.07 5 23.38 4.00 8
TOTAL 278.60 : 383.88

1993 crisscross 1 19.00 1 28.43 5.13 7
crisscross 2 5.00 1 30.29 11.76 7
crisscross 3 0.00 1 16.71 11.00 7
crisscross 4 8.00 1 13.43 2.99 7
crisscross 5 56.00 ‘I 84.71 16.85 7
tenniscourt 1 28.00 1 30.33 5.28 6
tenniscourt,2 14.00 1 22.50 5.17 6
tenniscourt 3 49.00 1 70.83 9.41 6
tenniscourt 4 19.00 1 21.00 2.76 6



* abandonment).

5-year high of 1355 and significantly altered the dynamic between crevice and cliff-top
habitat. Prior to 1995, cliff-top nesters had comprised 75-80% of the attending population;
however in 1995 cliff-top attendance dropped to 59% (Table 1; Figure 3).

Eight of the nine multiple-count crevice subcolonies experienced an increase in attendance
(Figure 4; Table 2). Two of subcolonies (CC2,3) had attendance counts higher than the
1991 pre-spill counts. The only subcolony which declined (TC4) was taken over by
Pelagic Cormorants (Parrish, pers. obs.). Despite this interspecific nesting habitat

competition, murres managed to attend, if not nest, in nearly equal numbers as in previous
years (Figure 4, Table 2).

During the 1995 nesting season, four aerial surveys were conducted by Ulrich Wilson of
the U. S. Fish and Wildlife Service Coastal Refuge Office. University of Washington
personnel were present for three of the four overflights such that groundtruths could be
made (Table 3). In all cases, land-based counts were higher than aerial counts. Excluding
zeros, aerial counts ranged from 14 to 89% of land-based counts. In general, differences
were smaller as a function of total subcolony size (compare Pole Island #023 to North
Island #022; Table 3) and time of season (e.g. late July counts were closer together than
June counts). The Main Island (#021) counts had the lowest correspondence; aerial counts
were 14-43% of land-based counts; however, this is understandable as there were 5 cliff-
top subcolonies and 25 crevice subcolonies on this part of Tatoosh spread over the
southwest to southeast facing cliffs. Furthermore, land-based counts were integrated over
several days, minimizing the chance of incorporating anomalies (e.g. temporary subcolony

Pl sy

In 1995, eggs appeared on both the crevice and cliff-top subcolonies by mid-June (Figure
5). This is at least 7-10 days later than 1992 and 1993, when eggs were present in early
June. However, the onset of egg production does not seem to determine in large part the
onset of hatching, probably because early eggs are victims of egg predation (Parrish pers.
obs.). Although the timing of egg laying did not appear to be habitat specific in 1995
(compare with 1993; Figure 5), chick hatching was. This pattem is also typical of previous
years (Figure 5); crevice eggs hatch before cliff-top eggs. Although this could be because
cliff-top nesters brood longer, it is more probably due to a more intensive cycle of laying
and loosing eggs early in the season in the cliff-top subcolonies (see below), such that
chicks are hatching from relays and/or first eggs laid relatively late. The discrepancy in

13



Table of Contents
Cover Page
Acknowledgments
Table of Contents
List of Figures and Tables
Introduction
Methods
Attendance
Phenology
Reproduction
Eagles
Results
Attendance
Phenology
Reproductive Success
Mitigating Factors - Eagles
Discussion
Conclusions
Citations

ANAAUNNe

wNN em
SSERRaQB



Miticatine F -Eagl
Common Murre reproductive success on Tatoosh Island is influenced by two major forces:
food availability and predators. In 1995, food appeared to be sufficient; however,
reproductive success was still low on the cliff-top subcolonies, primarily due to Bald Eagle
facilitated egg predation by gulls and crows. In-1995, 174 murre eggs were either
observed being removed by gulls and crows, or found broken in traditional gull/crow areas
(Parrish pers. obs.; Table 6). In both 1994 and 1995, the majority of lost eggs were from
the MCT: counting eggs on and under this subcolony, 68% (1994) and 55% (1995) of all
observed eggs (Table 6). Although there may be significant egg loss from other cliff-top
subcolonies, this is difficult to determine as eggs are not directly visible without visitation.

It is not known to what degree these totals (particularly the “other” category which includes
eggs lost from crevice subcolonies) reflect relaying.

Egg loss is correlated with daily attendance pattems (i.e. Table 4, Figure 6). Cliff-top

nesters, exemplified by the MCT, rarely spent an entire day on the subcolony. Eggs which

had been laid the previous evening/early morning, were lost when adults left the breeding

, area, Murres evacuated from the MCT primarily in response to overflights by Bald Eagles
(Table 7). From 1992-1995, 71 partial and 34 total evacuations have been witnessed. Of
these, the majority have been associated with the presence of eagles. Once murres left the.
subcolony, resettlement was gradual, occasionally lasting overnight if ensuing eagle
overflights occurred (Parrish pers. obs.). For resettlements which were completed without
interruption (defined as timed from the point of evacuation to the point at which murres

~ began to enter the salmonberry cover - usually at 1/4 to 1/3 of total attendance) the average
time to salmonberry entry was 44.8 + 36.5 minutes (X + SD, N=7, range 16-120; data
from 1991-1993). Thus, even in the best circumstances following a single eagle
overflight, eggs were left undefended for almost 3/4 of an hour.

Murres temporarily evacuated the MCT in response to a variety of disturbance events
including eagle overflights, researcher effects, and unknown events. In order to quantify
these events and calculate the relative effects of researchers on murre behavior and
reproductive success, the amount of time the subcolony was full, partially full, and empty
was recorded and categorized by disturbance causing murres to leave, if known.
Comparisons were made during two trips in June when eggs were being laid. (Before
these trips murres had not yet started to lay and afterwards murres on the MCT had given
up laying for the season.) Out of a total 1115 minutes watched, the subcolony was full

22


Acknowledgments :
The author wishes to thank the Makah Tribal Nation and the U. S. Coast Guard for
continued access to Tatoosh Island. As Makah college student intern, Neuee Vitalis helped
collect field data as well as contribute to its analysis. Karen Jensen, Johanna Salatas, Trista
Patterson and Jennifer Ruesink provided needed field and laboratory assistance. Dr.
Robert T. Paine assisted with logistics and accomodations, and graciously provided data on
Common Mune raft sizes and Bald Eagle visitation. Additional logistical support was
provided by the Olympic Coast National Marine Sanctuary (OCNMS) research vessel
TATOOSH and its captain, George Galasso. Fred Felleman provided prints of Common
Murres nesting in crevices on Rainbow Rock (#035) in August. Tom Owens of WDFW
provided data principally collected by Anita MacMillan on Bald Eagle nesting territories in
the vicinity of Tatoosh Island. Roy Lowe and David Pitkin of the USF&WS Kindly
provided detailed comments on Common Murre-Bald Eagle interactions on Three Arch
Rocks, Oregon. Ian Jones and Fred Cooke provided information and the opportunity to
- visit Triangle Island, British Columbia. Ed Bowlby of the OCNMS provided information
on Common Murre-Bald Eagle interactions on Tatoosh in mid-July. Mary Mahaffy
reported on Common Murre censuses conducted by USFWS personnel at the 13 December
_ 1995 meeting of the Tenyo Maru Trustee’s Council. Earlier drafts of this Teport were
improved by Mary Mahaffy and Ken Warheit. Funding for this project was provided by
the Tenyo Maru Trustee’s Council to the University of Washington in conjunction with the
Makah Tribal Nation,


(in the form of added cover mimicking natural vegetation) increased egg production and
were inversely proportional to percent of murres leaving (see also Figure 6, Table 4).
Finally, Parrish (manuscript) has shown that murres not only respond to the actual
presence of eagles, but more importantly to audio cues given by Glaucous-winged Gulls.
In concert, these experiments suggest that the interactions between these community
members are complex and need to be considered when attempting to influence murre
demographics, particularly reproductive success.

Conclusions

If the present patterns of attendance and reproductive success of the Tatoosh Island
Common Murres continue (assuming minimal immigration), the population may become
smaller and eventually reside mostly in crevices. Whether a reduced population size will be
viable in light of the factors affecting adult mortality (i.e. oil spills, gillnet by-catch, ENSO
and other oceanographically-induced changes in food supply) is unknown. The rapidity of
this habitat “switch” will probably be strongly influenced by immigration rate. In the
1980’s, the Tatoosh population increased dramatically as a function of immigration - almost
all of which went into the creation of cliff-top subcolonies. At present, these same birds
may be in the process of moving into crevices and/or abandoning Tatoosh as a viable
nesting colony. However, another wave of immigrants may change this pattern yet again.
As murre colonies south of Tatoosh appear to be increasing in size, immigration may again
become an important determinant of Tatoosh murre population size.

Citations :
Boekelheide, R. J., Ainley, D. G., Morrell, S. H., Huber, H, R., and Lewis, T. J. 1990.
Common mune. In: irds of t! ral lands. Ainley, D. G. and Boekelheide,

R. J. (eds.) Stanford University Press, Stanford, CA. pp:245-275.

Gaston, A. J., DeForest, L. N., Donaldson, G., & Noble, D. G. 1994. Population
parameters of Thick-billed Murres at Coasts Island, Northwest Territories, Canada.
Condor 96:935-948.

Halley D. J. & Harris, M. P. 1993 Intercolony movement and behaviour of immature

Guillemots Uria aalge. Ibis 135:264-270.

Harris, M. P. 1989. Variation in the correction factor used for converting counts of
individual guillemots Uria aalge into breeding pairs. Ibis 131:85-93.

Hedgren, S. 1980. Reproductive success of guillemots Uria aalge on the island of Stora
Karlsé. Oris. Fenn. 57:49-57.


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Figure 8. The maximum number of Bald Eagles sighted concurrently per rescarch trip to Tatoosh,
averaged over the periods of March-July, 1981-1995. Numbers inside each bar are rescarch trips.
Data provided by Dr. Robert T. Paine. This figure is reproduced from Parrish and Paine (manuscript).




Table 2 - Average attendance counts from BBPT (1991-1995) during egg/chick period for monitored
crevice subcolonies.

TOTAL 198.00 318.24
1994 crisscross 1 27.13 4.64 15 29.31 5.25 16
crisscross 2 31.50 13.75 14 35.50 9.17 16
crisscross 3 21.07 8.18 15 26.69 9.67 16
crisscross 4 11.33 5.42 15 17.35 13.53 17
crisscross 5 76.47 16.17 15 85.53 12.80 15
tenniscourt 1 20.43 8.71 14 28.53 7.76 17
tenniscourt 2 12.71 8.43 14 19.53 9.68 17
tenniscourt 3 35.29 23.45 14 64.35 26.34 17
tenniscourt 4 18.77 4.51 13 21.25 4.80 16

TOTAL 254.70 328.05
1995 crisscross 1 36.57 4.72 7 37.82 3.84 11
- crisscross 2 41.43 8.62 7 53.82 12.29 11
crisscross 3 49.71 11.79 7 57.09 8.07 ll
crisscross 4 19.57 5.09 7 21.00 5.51 11
crisscross 5 100.52 13.61 7 114.00 14.81 11
tenniscourt 1 35.57 6.21 7 40.09 3.94 11
tenniscourt 2 20.86 3.98 7 25.73 3.44 11
tenniscourt 3 72.00 12.68 7 77.00 8.45 11
tenniscourt 4 15.86 2.97 7 19.45 5.57 ll

TOTAL 446.00

392.10