Draft THE WESTERN GREBE ON SWAN, OKANAGAN, AND SHUSWAP LAKES

by Richard J. Cannings, R.P.Bio. and Kayla Feldman

March 14, 2000

Cannings Holm Consulting 1330 Debeck Road R.R. # 1, S. 11, C. 96 Naramata, B.C. V0H 1N0

This project has been funded by the Habitat Conservation Trust Fund. This fund was created to preserve, restore and enhance key areas of habitat for fish and wildlife throughout . Hunters, anglers, trappers and guides contribute to HCTF enhancement projects through licence surcharges. Tax deductible contributions to assist in the work of HCTF are also received. i

SUMMARY

Western Grebes nest at only 3 sites in British Columbia. A former breeding site, Swan

Lake near Vernon, seems to be still suitable for Western Grebes. We undertook this study in an attempt to understand why the species abandoned the site in the late 1970s or early 1980s. We compared conditions at with two nearby colonies at the north end of and at Arm on Shuswap Lake. At all sites we studied various habitat parameters, disturbance by boaters, prey availability, lake level fluctuations and presence of potential nest predators.

Western Grebes were seen on Swan Lake, but only during spring migration in

May. The colonies at Okanagan Lake and were both unsuccessful this year.

The Okanagan Lake colony was abandoned and partially predated for unknown reasons; the Salmon Arm colony was flooded by extreme high water levels that persisted from mid-June through late July.

Habitat analyses indicated that Swan Lake is suitable for Western Grebe colonization—sufficient stands of open Scirpus marsh are available and small fish populations seem high. Disturbance by boats on Swan Lake is low, particularly that involving high-powered ski boats. Water level fluctuations at Swan Lake are the least of the three sites and well within tolerance limits for grebes. Predator numbers are also relatively low at Swan Lake.

We noticed that incubating birds at the Okanagan Lake colony left their nests when we approached by kayak to within 50 to 100 m of the colony. Since repeated disturbance of this sort may be detrimental to any grebe colony, we feel that it would be ii worthwhile to consider limiting boat activity of all types on a portion of Swan Lake to minimize such disturbance. An assessment of habitat availability and obvious points of boat access suggests that the north end of the lake would be best for this purpose, with perhaps a smaller secondary no-boating area at the south end. iii

TABLE OF CONTENTS SUMMARY...... I

LIST OF FIGURES ...... IV

LIST OF TABLES ...... IV

INTRODUCTION...... 1

STUDY SITES...... 3

METHODS...... 3

CENSUSES ...... 3 WATER LEVELS ...... 7 NEST SURVEYS...... 7 DISTURBANCE STUDIES ...... 7 PREY AVAILABILITY ...... 8 HABITAT ...... 8 FORAGING BEHAVIOUR ...... 9 RESULTS ...... 9

CENSUSES ...... 9 WATER LEVELS ...... 10 NEST SURVEYS ...... 10 Swan Lake ...... 10 Okanagan Lake ...... 15 Salmon Arm...... 17 DISTURBANCE...... 17 PREY AVAILABILITY ...... 18 HABITAT ...... 22 Swan Lake ...... 22 Okanagan Lake ...... 22 Salmon Arm...... 23 FORAGING BEHAVIOUR ...... 23 POTENTIAL NEST PREDATORS...... 24 DISCUSSION ...... 30

ACKNOWLEDGEMENTS...... 32

REFERENCES...... 33 iv

LIST OF FIGURES

1. Swan Lake...... 4 2. Okanagan Lake, north end ...... 5 3. Salmon Arm...... 6 4. Western Grebe censuses...... 12 5. Red-necked Grebe censuses...... 13 6. Lake Levels...... 14 7. Boat Activity...... 19 8. Disturbance Rates on weekends vs. weekdays...... 21 9. Foraging rates ...... 26 10. Foraging rates at half-hour intervals ...... 27 11. Western Grebe nest, Okanagan Lake ...... 28 12. Western Grebe nest (predated), Okanagan Lake...... 28 13. Nest-like structure built by Western Grebes in milfoil mat, Okanagan Lake...... 29 14. Red-necked Grebe nest (eggs covered) in clump of bulrush, Swan Lake ...... 29

LIST OF TABLES

1. Distribution of disturbance studies at each site...... 8 2. Red-necked Grebe nests at Swan Lake...... 11 3. Western Grebe nests found on 25 June 1999...... 15 4. Western Grebe nests at Okanagan Lake, 29 July 1999...... 16 5. Numbers of fish caught in minnow traps at the three sites...... 19 6. Shoreline habitats at Swan Lake and the north end of Okanagan Lake...... 22 1

INTRODUCTION The Western Grebe (Aechmophorus occidentalis) breeds on marshy lakes in the interior of western North America and winters on the Pacific Coast of North America, primarily along the coast of British Columbia (Campbell et al. 1990). It is highly gregarious at all seasons, breeding in colonies and wintering in flocks that can number into the thousands.

These gregarious habits and its reliance on wetland habits have made the Western

Grebe a species of concern for some time. It was on the National Audubon Society Blue

List of species in decline from 1973 to 1982 (Tate 1981, Tate and Tate 1982), with habitat losses blamed for this decline. In 1986 it was downlisted to a species of “Special

Concern” by Tate (1986), with a request for more information on its current status.

Western Grebes are on the British Columbia Red List. The provincial breeding population is less than 200 pairs and is thought to be declining (Burger 1977). One of the major factors in their Red List status is that these 200 pairs nest in only three colonies in

British Columbia: Shuswap Lake at Salmon Arm; the North Arm of Okanagan Lake; and

Duck Lake near Creston.

Western Grebes formerly nested at Williams Lake and on Swan Lake near

Vernon, but these colonies have been inactive since the 1960s (Cannings et al. 1987,

Campbell et al. 1990). The Williams Lake colony was active from at least 1935 (Munro

1939) to 1964 (Campbell et al. 1990), and involved about 50 pairs at its height in 1941

(Munro 1941). Western Grebes have also nested at and the delta, but these breeding sites were only used once or twice (Campbell et al. 1990).

The Swan Lake colony was discovered in 1933 (Munro 1935) when adults with downy young were seen on the lake. On June 7, 1950, about 85 adults were on Swan 2

Lake and two groups of nests with 17 nests in total were found in Scirpus marshes on the east side of the lake (Munro 1954). On June 7, 1951, 75 adults were observed and one nest and one newly hatched young were seen, but no nest searches were undertaken

(Munro 1954). The Swan Lake colony was suspected of being active in 1978 (Cannings et al. 1987), but no nesting activity has been observed there since other than one brood of young was seen there in 1990 (Burger 1997).

The Salmon Arm colony was discovered in 1962 (Campbell et al. 1990) and has had as many as 96 pairs nesting (in 1996; Kime and Kime 1996). The colony at the north end of Okanagan Lake was first discovered in 1977 and involved 83 pairs of grebes in

1986 (Campbell et al. 1990). The Swan Lake colony thus declined and disappeared as the Okanagan Lake colony was appearing, and therefore may have simply moved from one site to the other.

Several factors have been suggested as possible reasons for the demise of the Swan

Lake colony (O. Dyer, unpublished notes):

• Increased boating activity, floatplane use and other human disturbance may have

induced the grebes to nest elsewhere

• Habitat disturbance by livestock

• Wash from the wakes of power boats may have destroyed nests

• Emergent vegetation may have become too dense for nesting

• The spread of Eurasian milfoil (Myriophyllum spicatum) may have choked out former

foraging areas

• Fluctuations in water depth may have flooded nests

• Prey population composition and/or density may have changed 3

The present study was an attempt to discover how Swan Lake differs from the two nearby active colonies—those at the North Arm of Okanagan Lake and at Salmon Arm— in an effort to design future management plans that could allow the grebes to nest successfully at Swan Lake.

STUDY SITES Swan Lake is a 4.5-km2 lake located at the north end of Vernon, BC (Figure 1). Much of the shoreline is marshy, with healthy stands of bulrush (Scirpus acutus) and cattail (Typha latifolia). Land tenure around the lake is largely private and the north end is Indian

Reserve, although there is a Crown Land reserve for wildlife conservation adjacent a property owned by the Nature Trust of British Columbia on the east shore.

The comparison sites (active colonies) are at the north end of Okanagan Lake and on Shuswap Lake at Salmon Arm. The Okanagan Lake site (Figure 2) consists of three sub-colonies in extensive beds of emergent vegetation; the land adjacent to the lake is

Indian Reserve. The Salmon Arm site is along the foreshore on either side of a marina; nests are located among reed canarygrass (Phalaris arundinacea) (Figure 3).

METHODS

CENSUSES We censused Western Grebes and Red-necked Grebes (Podiceps grisegena) at each site at weekly intervals (at a minimum) from 3 May to 26 July. We carried out most censuses by viewing the sites with a 22 X spotting scope; on two occasions at each site we counted birds from a kayak while doing nest surveys. We censused Swan Lake from three vantage points (Figure 1): the dock at Silver Star campground, the end of Meadowlark

Road, and from the northeast corner of the lake. 4

Figure 1. Swan Lake, showing census viewing points and Red-necked Grebe 1999 nest sites. 5

Figure 2. Okanagan Lake north arm, showing Western Grebe 1999 nesting sites. 6

Figure 3. Salmon Arm, Shuswap Lake. Straight grey lines indicate general placement of marker buoys to delineate no-boat zone; grey ellipses indicate site of Western Grebe nesting attempts in 1999. Ring-billed Gull colony is on Christmas Island. 7

We censused Okanagan Lake from the shore at the trailer park (Figure 2), and Shuswap

Lake from the public wharf (Figure 3). During each census we also noted the numbers and species of possible nest predators, especially gulls and corvids.

WATER LEVELS We measured the lake level of Swan Lake to the nearest centimetre on each visit with a metre stick from the dock at Silver Star RV Park. We obtained levels for Okanagan Lake from the Ministry of Environment, Lands and Parks, Water Management Branch in

Penticton and levels for Shuswap Lake from the Water Survey of Canada, Vancouver.

NEST SURVEYS We carried out searches for grebe nests using a kayak. Swan Lake was searched on 25

June and 30 July, Okanagan Lake on 23 June and 29 July, and Shuswap Lake on 29 June and 28 July. During each nest survey the nests were counted, located using a hand-held

GPS unit, and the number of eggs noted. We also noted the emergent vegetation around the nest and measured the water depth at the nest site.

DISTURBANCE STUDIES We measured disturbance levels by counting the number of boats using each site during a

30-minute interval. These intervals were distributed as evenly as possible throughout the day, week and the season at each site (Table 1). We did not attempt to measure the speed of the boat or its proximity to grebes, but simply classified the boat into the following categories: High-powered (e.g. water-skiing boat); low-powered (e.g. fisherman trolling); unpowered (e.g. canoe); seaplane; and houseboat. 8

Table 1. Distribution of disturbance studies at each site.

Site Week-day Weekend Morning Midday Afternoon Swan104 131414 Okanagan 10 4 13 14 14 Salmon 7 5 121212 Arm

PREY AVAILABILITY We studied prey availability using four minnow traps. We set these at Swan Lake on 15 and 23 July, at Okanagan Lake on 16, 17, 24 and 25 July, and at Salmon Arm on 18 and

26 July. We measured the length of each fish caught and photographed it for future identification. Unfortunately, we were unable to identify each individual to species because of camera problems.

HABITAT We mapped the habitat at Swan Lake and Okanagan Lake from a kayak using a hand-held

GPS unit. We noted the dominant emergent vegetation (bulrush or cattail) and, if bulrush, whether the stands were dense (mean distance between stalks generally < 5 cm), clumped (discrete groups of densely packed stalks) or sparse (mean distance between stalks > 5 cm). Habitat at Salmon Arm was more problematical since for most of the spring and summer there was no emergent vegetation because of extreme water levels.

We mapped habitat there on a very broad scale by simply noting vegetation type.

We also assessed habitat with nest-centred methods (see Nest Surveys), but since no nests were visited at Salmon Arm there was no nest-centred data from that site. 9

FORAGING BEHAVIOUR We studied foraging behaviour of Western Grebes at Okanagan Lake and Salmon Arm in two ways. In May we timed the foraging dives of individual birds to assess differences at the two sites, and in June and July we sampled grebe flocks during the day to assess what proportion of the birds were foraging or resting/alert during morning (0900-1030), midday (1200-1330) and afternoon (1500-1630) periods.

RESULTS

CENSUSES Numbers of Western Grebes are summarized in Figure 4 and numbers of Red- necked Grebes in Figure 5. A few Western Grebes used Swan Lake during spring migration, but none were recorded after 17 May. All were seen from the Meadowlark

Road site; the birds were generally in the centre of the lake or more towards the western shore. We saw no Western Grebes on Swan Lake near suitable breeding habitat and saw no breeding activity there. Maximum numbers seen at Okanagan Lake and Salmon Arm were 115 and 162 respectively.

Red-necked Grebes were essentially absent from Okanagan Lake, but about 10 pairs nested on Swan Lake. Red-necked Grebe numbers on Swan Lake were concentrated at the north end, where the mean of 6.2 birds/census (range 0-10) was significantly higher than means of 2.9 (0-7) at the south end and 1.3 (0-4) off

Meadowlark Road. Red-necked Grebe numbers were low at Salmon Arm through May and June, but small groups appeared in July to a maximum of 14 birds on 28 July. Only one or two pairs nested at Salmon Arm, so most of these arrivals were likely failed breeders from elsewhere. 10

We saw single Clark’s Grebes (Aechmophorus clarkii) at Okanagan Lake (July

30) and Salmon Arm (17 June, 14 and 15 July). The Clark’s seen on 17 June at Salmon

Arm was a female paired with a male Western; on the same day Frank Kime reported a male Clark’s at Salmon Arm so there may well have been two Clark’s Grebes there.

WATER LEVELS Water levels at the three lakes are shown in Figure 6. Shuswap Lake shows by far the greatest fluctuation in water levels with an increase of almost 3 m from early May through late June. During the same period, the level of Okanagan Lake (which is controlled by a dam at Penticton) rose about 1 m and Swan Lake only about 60 cm. The level of Shuswap Lake stabilized briefly during the second week of June at about 348.25 m, but climbed sharply again to a peak of 349.22 m by the end of the month and remained unusually high until the middle of July.

NEST SURVEYS Swan Lake

No Western Grebes nested on Swan Lake in 1999, but 10 or 11 pairs of Red-necked

Grebes did so. We found 11 Red-necked Grebe nests at Swan Lake on 25 June (Table 2).

Five of these contained eggs, while 6 were empty, though in at least one of the latter cases a pair was swimming close off shore. On 30 July we located 7 nests, 4 of them with eggs and 3 empty. Although we did not mark any of the nests, we are confident that most, if not all, are different. Numbers 10 and 14 may be the same nest based on GPS and habitat information. We did not see any young grebes on Swan Lake, although a brood of 2 11 young was reported on 15 July (Russell Cannings pers. comm.) and we did not survey the lake after 30 July.

Table 2. Red-necked Grebe nests at Swan Lake.

Date Nest UTM coordinates Eggs Water Habitat No. (NAD 27) Depth (cm) 25 June 1 5574595N 0 91 in Scirpus 25 June 2 5575430N 2 85 in clumped Scirpus with some Chara 25 June 3 5575877N 2 58 of willow twigs and algae; in patch of Rumex 25 June 4 5577331N 0 74 in Scirpus clump 25 June 5 5577696N 0 70 in Scirpus clump 25 June 6 5577700N 0 68 in Scirpus clump 25 June 7 340076E 5578264N 2 105 in clumped Scirpus 25 June 8 340080E 5578290N 0 - in sparse Scirpus 25 June 9 340295E 5577529N 3 64 in Typha clump 25 June 10 5577170N 0 76 in clumped Scirpus 25 June 11 339749E 5575794N 1 66 in sparse Scirpus 30 July 12 340284E 5577884N 3 79 in clump of Scirpus off Typha bed 30 July 13 340250E 5577222N 5 68 in Scirpus clump 8 m out from Typha 30 July 14 340237E 5577124N 0 77 in Scirpus clump 15 m offshore 30 July 15 338926E 5574940N 4 80 in band of Scirpus 4 m out from Typha 30 July 16 338926E 5574970N 1(broken) 80 in clump of Scirpus 30 July 17 338930E 5575010N 0 - in clump of Scirpus out from Typha 30 July 18 338817E 5575407N 0 67 - 12

Figure 4. Western Grebe Censuses

180

160

140

120

100 Swan Lake Okanagan Lake 80 Salmon Arm

60 Number of Western Grebes Western of Number

40

20

0

9 9 9 9 9 9 9 9 9 9 9 9 -9 -9 -9 -9 -9 9 9 9 9 9 9 9 r r y y y n- n- n- ul- ul- ul- g- Ap Ap a a a u u u -J -J -J u 0- 0- -M -M -M -J -J -J 9 9 9 -A 2 3 10 20 30 09 19 29 0 1 2 08 Date 13

Figure 5. Red-necked Grebe censuses 25

20

15

Swan Lake Okanagan Lake 10 Salmon Arm Red-necked Grebe numbers Grebe Red-necked

5

0

9 9 9 9 9 9 9 9 9 9 9 9 r-9 r-9 y-9 y-9 y-9 -9 -9 -9 l-9 l-9 l-9 -9 p p a a a un un un Ju Ju Ju ug -A -A -M -M -M -J -J -J 9- 9- 9- -A 20 30 10 20 30 09 19 29 0 1 2 08 Date 14

Figure 6. Lake Levels

350

300

250

200 Shuswap Okanagan Swan 150 Lake Level (cm) Level Lake

100

50

0

19/04/9926/04/9903/05/9910/05/9917/05/9924/05/9931/05/9907/06/9914/06/9921/06/9928/06/9905/07/9912/07/9919/07/9926/07/9902/08/9909/08/9916/08/9923/08/9930/08/99 Date 15

Okanagan Lake

On 25 June we found 14 Western Grebe nests in two small groups along the east shore of the lake (Figure 2). Six of these nests contained eggs, 4 were empty, and 4 had been recently predated (Table 3). On 29 July we found 42 nests at the northernmost site discovered on 25 June. All these nests were abandoned and/or predated; 10 were empty

(Table Z). We found no nests at the southern site on 29 July.

Table 3. Western Grebe nests found on 25 June 1999 at the north end of Okanagan Lake.

Nes UTM Eggs Water Habitat t depth No. (cm) 1 335490E 5577813N 2 - in open Scirpus 2 335511E 5577757N 3 61 in open Scirpus 3 335510E 5577750N 0 - in open Scirpus 4 335510E 5577750N 0 - in open Scirpus 5 335379E 5577785N 5 92.5 in open Scirpus in small “island” of Scirpus 6 335379E 5577785N 4 92 in open Scirpus in small “island” of Scirpus 7 335379E 5577785N 0 - in open Scirpus in small “island” of Scirpus 8 335379E 5577785N 0 - in open Scirpus in small “island” of Scirpus 9 335379E 5577785N 2 100 in open Scirpus in small “island” of Scirpus 10 332360E 5574949N 1 (predated) 60 in open Scirpus 11 332360E 5574949N 2 (predated) 49 in open Scirpus 12 332360E 5574949N 1 (predated) 56 in open Scirpus 13 332360E 5574949N 2 (predated) 49 in open Scirpus 14 332154E 5574644N 4 60.5 in open Scirpus 16

Table 4. Western Grebe nests at Okanagan Lake, 29 July 1999.

Nest No. Eggs Water Depth (cm) 1 3 (1 broken) 60 2 2 broken 55 3 2 (1 broken) 81 4 2 broken 90 5 1 broken 87 6 2 broken 100 7 0 100 8 2 broken 94 9 1 broken 99 10 1 91 11 1 broken 83 12 egg shells 86 13 0 73 14 0 67 15 1 83 16 3 (2 broken) 86 17 4 86 18 0 80 19 1 broken 78 20 2 broken 76 21 2 broken 72 22 4 (3 broken) 80 23 1 broken 72 24 4 broken 75 25 2 broken 68 26 3 broken 70 27 2 broken 65 28 2 broken 78 29 0 77 30 2 broken 80 31 0 80 32 1 broken 81 33 1 broken 87 34 3 broken 92 35 1 broken 91 36 0 87 37 0 88 38 1 broken 89 39 3 (1 broken) 89 40 2 broken 86 41 0 87 42 0 90 17

Salmon Arm

On 17 June, Frank Kime reported 35 Western Grebe nests in the area just west of the public wharf (in front of a relatively new housing development) and 14 nests in the shallows just shoreward of Christmas Island. The birds had apparently built these nests and begun to lay eggs after a few days of stable water levels starting about 10 June. We scheduled a thorough nest search for 29 June, but a heavy storm on 19 and 20 June caused the water levels to rise abruptly and the combination of high water, winds and waves destroyed all the nests. On 24 June we could see no nests west of the wharf and only 2 nests near Christmas Island. Our kayak-based survey on 29 June failed to locate any Western Grebe nests, although we did find an empty Red-necked Grebe nest in canary grass at 339876E 5621710N (NAD 27). We also found an American Coot nest that day at 339800E 5620210N, but the 7 eggs were literally floating in the water. We repeated the kayak survey on 28 July, but the only evidence of grebe breeding we could find was a brood of 3 young Pied-billed Grebes with an adult in marshes along the east shore of the bay. Frank Kime reports that he saw 3 broods of Western Grebes later in

August, with a total of 5 young in all, so some Western Grebe nests must have survived the high waters of July, probably hidden in Scirpus marshes along the east shore of the bay.

DISTURBANCE The results of disturbance surveys are summarized in Figure 7. The Salmon Arm site has much more boat activity than the other two sites, but this is tempered by the roped off area on either side of the marina (Figure 3), which keeps all boats away from nesting 18 grebes. This measure appears to be highly effective in reducing disturbance to the birds.

Boat activity was significantly higher on weekends at all sites. The number of boats active on weekends was about 2 to 3 times that for weekdays (Figure 8).

There is one active seaplane moored at the Salmon Arm wharf, and at least 5 at wharves and hangars around Swan Lake. Swan Lake is generally not used as a water skiing site, but there is one active ski boat with jump set up on the central western shore of the lake. A water ski slalom course was set up along the west shore of Okanagan Lake just north of the point marking the north end of Newport Beach. Another possible source of human disturbance at Swan Lake is the rowing club, which has a course set just north of the radio towers near Meadowlark Road on the east shore.

One important observation we made concerning disturbance is that when approaching the Okanagan Lake colony by kayak, the incubating birds would slip off their nests and dive underwater when we were about 50 to 100 m away. This behaviour was so distinctive that it made locating the colony quite simple—we just had to watch for a number of birds suddenly appearing off a marsh where there had been no birds moments before. This suggests that even canoe, kayak or slow motorboat traffic—if regular enough—could significantly disturb a colony or simply leave it vulnerable to predation. Penny Ohanjanian (pers. comm.) has also made this observation at the Duck

Lake colony.

PREY AVAILABILITY The number of fish found in the minnow traps was roughly similar for Salmon Arm and

Swan Lake, but considerably lower at Okanagan Lake (Table 5). The reasons for this difference are not clear, but may relate to habitat differences at the trap sites themselves. 19

A much more thorough study of the fish fauna of the three sites would be necessary to make a full assessment of this aspect of suitability, but this cursory examination shows that Swan Lake is not completely unsuitable. Unfortunately, most fish caught were unidentified, but sculpins (Cottus sp.) were caught at all three sites and a pumpkinseed

(Lepomis gibbosus) was caught at Swan Lake.

Table 5. Numbers of fish caught in minnow traps at the three sites.

Swan Lake Okanagan Lake Salmon Arm No. fish caught 12 5 16 Trap-nights 8 16 8 Fish/trap-night 1.5 0.3 2.0 Mean length (mm) 4.8±0.5SE (3.2-9.1) 5.4±0.8SE (3.7-8.4) 4.1±0.1SE (3.2-5.1) 20

Figure 7. Boat Activity

9.00

8.00

7.00

6.00

5.00 Swan Lake Okanagan Lake 4.00 Salmon Arm

Incidents per 30 minutes 3.00

2.00

1.00

0.00 High Power Low Power Non-motorized Sea plane Houseboat Total Motorized Boats Motorized Boats boats Boat Type 21

Figure 8. Disturbance rates on weekends vs. weekdays

14

12

10

8 weekends weekdays 6 Incidents/30 min. Incidents/30

4

2

0 Swan Lake Okanagan Lake Salmon Arm Site 22

HABITAT Swan Lake

The shoreline habitats of Swan Lake were grouped into cattail, bulrush and bare; the bulrush category was further divided into solid bulrush, sparse bulrush and clumped bulrush. The extent of these habitats are summarized in Table 6.

Table 6. Shoreline habitats at Swan Lake and the north end of Okanagan Lake. Length of shoreline Percentage of shoreline Swan Okanagan Swan Okanagan Bare (no emergent vegetation) 200 5600 2 56 Cattail (Typha latifolia) 1440 500 13 5 Bulrush (Scirpus acutus) Solid 3085 1100 45 11 Sparse 1270 2800 12 28 Clumped 4985 28

Nest-centred habitat studies showed a clear tendency for Red-necked Grebes to nest in clumps of bulrush rather than in the other categories of emergent vegetation—12 of 17 nests were in bulrush clumps or bands, 3 in sparse bulrush stands, 1 in cattails and 1 in a clump of flooded dock (Rumex). Water depths at 16 nests ranged from 58 to 105 cm

(mean 75.5±2.9SE). This mean depth is not significantly different from that found for

Western Grebes at Okanagan Lake (see below).

Okanagan Lake

Unlike Swan Lake, the north arm of Okanagan Lake has considerable stretches of bare shoreline interspersed with smaller sections of bulrush and only two or three areas of cattail. There was less tendency for bulrush on Okanagan Lake to be clumped, it was instead mapped simply as solid or sparse. All Western Grebe nests found on Okanagan 23

Lake were in sparse bulrush stands. The water depth at 51 nests ranged from 49 to 100 cm (mean 79.6±1.9SE), very similar to the depths at Red-necked Grebe nests on Swan

Lake.

Salmon Arm

The Salmon Arm site has a completely different habitat structure than Swan Lake or the north arm of Okanagan Lake. The Salmon Arm foreshore is dominated by reed canarygrass (Phalaris arundinacea) throughout most of its length. There are small areas of cattail and bulrush marsh in the southeast corner of the bay, and water smartweed

(Polygonum amphibium) is a common dominant in deeper waters to the east of the wharf and around the Salmon River mouth. Willows (Salix spp.) are common at the river mouth as well, and have been used in the past as grebe nesting habitat (F. Kime, pers. comm.).

FORAGING BEHAVIOUR The time Western Grebes spent underwater during individual foraging dives differed between Okanagan Lake and Salmon Arm. The mean length of 42 dives at Okanagan

Lake was 38.7 sec (±4.2SE, range 6-103), while the mean length of 86 dives at Salmon

Arm was 21.2 sec (±1.3SE, range 4-63). This difference is statistically significant (t-test, p < 0.0002), but the biological significance is unclear. A possible explanation is a difference in water depth; foraging birds at the Okanagan Lake site were diving in water that was 10 to 20 m deep (from bathymetric map), while those in Salmon Arm were mostly in water that was less than 5 m deep. Birds were observed catching fish so rarely 24

(only once in 128 dives) it was impossible to assess the difference in actual capture rates between the two sites.

The proportion of birds in a flock that were foraging was about 20 % through the mid-morning and midday periods, then dropped to about 10 % by mid-afternoon. This change is illustrated in Figure 9, which shows activity patterns at Okanagan Lake and

Salmon Arm, and in Figure 10, which shows these patterns from both sites combined on a more detailed time scale.

POTENTIAL NEST PREDATORS

Birds regarded as potential nest predators (corvids and large gulls) were generally not common at either Swan Lake or Okanagan Lake. We counted a total of 60 large gulls

(range 0-23) on 18 visits to Swan Lake and a total of 8 (0-3) on 23 visits to Okanagan

Lake. The situation at Swan Lake was completely different. There, approximately 400 pairs (i.e. 800+ individuals) of Ring-billed Gulls (Larus delawarensis) nested on

Christmas Island, a dredge-spoil area in the southeast corner of the bay. While these gulls nested there and often loafed on the public wharf and the nature area viewing tower, they seemed to feed mostly on the farm fields of the Salmon River valley. There, they followed tractors pulling ploughs, presumably looking for mice and large insects. This large colony of Ring-billed Gulls has been a concern to those interested in the well-being of the Western Grebes at Salmon Arm, but at least on one occasion (1996) the grebes nested successfully en masse in the shallows around Christmas Island, literally in the shadow of the gull colony (Kime and Kime 1996). This year some of the grebes 25 attempted to nest there again but were thwarted by rising waters (as were the gulls—most of their nests were inundated in 1999 as well).

Corvids were generally uncommon at all three sites. We saw crows (Corvus brachyrhynchos) only twice at Swan Lake, once at Okanagan Lake and three times at

Salmon Arm; all sightings involving only 1 to 3 birds. The only raven (Corvus corax) we saw was at the census point at Okanagan Lake. 26

Figure 9. Foraging Rates

0.2

0.18

0.16

0.14

0.12

Okanagan 0.1 Salmon Arm

Percent foraging 0.08

0.06

0.04

0.02

0 Morning Noon Afternoon Time of Day 27

Figure 10. Foraging rates at half-hour intervals

0.25

0.2

0.15

0.1 Percent of grebes foraging

0.05

0 0905- 0935- 1005- 1035- 1105- 1135- 1205- 1235- 1305- 1335- 1405- 1435- 1505- 1535- 1605- 1635- 0930 1000 1030 1100 1130 1200 1230 1300 1330 1400 1430 1500 1530 1600 1630 1700 Time of Day 28

Figure 11. Western Grebe nest, Okanagan Lake

Figure 12. Western Grebe nest (predated), Okanagan Lake 29

Figure 13. Nest-like structure built in milfoil mat, Okanagan Lake.

Figure 14. Red-necked Grebe nest (eggs covered) in clump of bulrush, Swan Lake. 30

DISCUSSION The reasons for the demise of the Western Grebe colony at Swan Lake are unclear.

Nesting habitat, if defined as sparse stands of bulrush as seems to be the case in

Okanagan Lake, seems to be still present in more than adequate amounts. Small fish are common, so prey supply is likely adequate as well. Water level fluctuations are clearly not a problem, or at least not the serious problem that they can be at Salmon Arm.

Swan Lake is exposed to winds and nest-damaging waves could be generated several times during a breeding season, but this is also the case at Okanagan Lake and

Salmon Arm. The growth of milfoil can also be ruled out, as this plant is restricted to small, rather inconspicuous patches in Swan Lake, while the huge growths in Okanagan

Lake actually seem to be favoured by the grebes as loafing sites and perhaps even for nesting. The milfoil mats on Okanagan Lake may even function to dampen wave activity onto the eastern shore of the lake where nesting seems concentrated.

Disturbance by livestock is much more likely at Okanagan Lake, where the main colony site this year was located immediately adjacent a barn and pasture with numerous horses. There is only one site on Swan Lake (a lot on the south side of Meadowlark

Road) where cattle actively drink and forage in the lakeshore marsh; there are no livestock presently on the Salmon Arm site.

Disturbance levels also seem to be relatively low when measured simply as the number of boats present on Swan Lake, and are certainly comparable or below those levels on Okanagan Lake. The colony may have moved from Swan Lake to the north arm of Okanagan Lake, since the dates of the birds leaving Swan Lake match closely with the first records from Okanagan Lake. Why the birds may have moved may never be known, 31 since it might have been due to temporary disturbance problems that are not present now, or may have been the result of a more or less random flock decision on the part of the grebes.

One likely possibility is that of repeated disturbance by boaters travelling along the marsh edge, close enough to have the birds slip off their nests and leave them for a matter of minutes. As alluded to in the Results section, if this low-level type of disturbance was repeated often enough, it could have resulted in breeding failure and colony abandonment. Swan Lake has relatively low numbers of boats as compared to

Okanagan Lake and Salmon Arm, but there are often canoes and small motorboats that travel close to the marshy margin of the lake. This is very different to the situation in

Salmon Arm, where all boating activity is restricted for several hundred metres out from the colony sites. The Okanagan Lake colony is open to this type of disturbance, but most of the boating activity takes place along the west side of the lake, and all nesting attempts took place on the eastern shore. This disturbance does not seem to affect other waterbirds such as Red-necked Grebes and American Coots, several of which nest within a few metres of waterfront lawns of residences along the west shore of Swan Lake.

The only management recommendation that we would make based on this study is a no-boat zone be set up at the northern end of Swan Lake. The exact boundaries of this zone would have to be negotiated with the adjacent landowners, including the Okanagan

Indian Band. A smaller no-boat zone could be established at the south end of the lake as well. This zone would likely be easier to establish, but while it would protect substantial numbers of migratory waterfowl that congregate around the mouth of BX Creek it would protect little in the way of potential Western Grebe habitat. 32

ACKNOWLEDGEMENTS

We thank Frank Kime, whose studies of the Western Grebes of Salmon Arm Bay over the last decade provided many interesting facts and a proper perspective on the long-term situation of this colony. Pat McAllister and Wendy Hook provided accomodations in

Vernon. We also thank the management of Silver Star campground and the trailer park at the head of Okanagan Lake, as well as the Okanagan Indian Band for allowing access to

Okanagan and Swan Lakes. Ondrea Rogers of the Salmon Arm Bay Nature Enhancement

Society was helpful in many ways. Steve Matthews (Ministry of Environment, Lands and

Parks, Penticton) generously loaned the minnow traps, and Brian Symonds (Ministry of

Environment, Lands and Parks, Penticton) and Lynne Campo (Water Survey of Canada) provided lake level data.

Finally, we thank Orville Dyer, Ministry of Environment, Lands and Parks,

Penticton for initially suggesting this study and giving us thoughtful suggestions at several junctures. 33

REFERENCES Burger, A. E. 1997. Status of the Western Grebe in British Columbia. BC Environment

Wildlife Working Report No. WR-87.

Campbell, R. W., N. K. Dawe, I. McTaggart-Cowan, J. M. Cooper, G. Kaiser, and M. C.

E. McNall. 1990 Birds of British Columbia, Volume 1. Royal British Columbia

Museum and Canadian Wildlife Service, Victoria, BC. 514 pp.

Cannings, R. A., R. J. Cannings, and S. G. Cannings. 1987. Birds of the Okanagan

Valley, British Columbia. Royal British Columbia Museum, Victoria, BC. 420

pp.

Kime, D. and F. Kime. 1996. The Western Grebe in the Salmon Arm Bay of Shuswap

Lake. Unpubl. report, Sunnybrae, Salmon Arm, BC. 4 pp.

Munro, D. A. 1954. Notes on the Western Grebe in British Columbia. Auk 71:333.

Munro, J. A. 1935. Recent records from British Columbia. Condor 37:178-179.

Munro, J. A. 1939. Nesting of the Western Grebe in British Columbia. Pp. K16-K17 in

Report of the Provincial Museum of Natural History for the year 1938, Victoria.

Munro, J. A. 1941. The grebes: studies of waterfowl in British Columbia. British

Columbia Provincial Museum Occasional Paper No. 3, Victoria. 71 pp.

Tate, J. 1981. The blue list for 1981. American Birds 35:3-10.

Tate, J. 1986. The blue list for 1986. American Birds 40:227-236.

Tate, J. and D. J. Tate. The blue list for 1982. American Birds 36:126-135.