Condor 8466-70 0 The Cooper Ornithological Society 1982

NESTING ECOLOGY AND PRODUCTION OF WESTERN AT BEAR RIVER MIGRATORY REFUGE, UTAH

MARK L. LINDVALL

AND JESSOP B. LOW

ABSTRACT.-The nesting ecology of Western Grebes (Aechmophorusocciden- t&is) was studied at Bear River Migratory Bird Refuge, Utah, in 1973 and 1974. Western Grebes nested on dry land, emergent vegetation, and in open-water areas in colonies and single nests. They selected sites near open water (approximately 30 cm in depth). At least one young hatched in 2 1% of the nests.Avian predation and abandonment of nests caused the largest losses.Mated pairs produced an average of 1.7 young.

Western nesting habits have been de- timeters at the heads of the units, to approx- scribed by several authors. Bent (19 19) char- imately 50 cm in the center of each unit, and acterized nests in North Dakota, California, to over 2 m along the dikes and canals. Hot and Saskatchewan, as floating in emergent dry summersare usual with an average annual vegetation. In Oregon, Finley (1907) found precipitation of 34 cm. The average minimum three or four eggsto be the usual clutch size. summer temperature is 19°C and the average Palmer (1962) summarized available infor- maximum temperature is 37°C. mation on the courtship behavior, range, We located nestsby driving plumage characteristics, nesting habits, and along the dikes or by rowing a small boat along food habits. Herman et al. (1969) and Rudd marshy edges.Most nestswere built along the and Herman (1972) described the effects of edgeof the deeper water and were easily found. DDT contamination on Western Grebes, and Nests were marked with a nest number on a Lindvall and Low (1979, 1980) reported on stake in nearby vegetation, and were visited organochlorine pesticide and PCB residuesin at three- or four-day intervals to collect data these grebes. on nesting habitat and nest success.Fate of Because the breeding biology of Western eggswas determined by examination for egg Grebes has received little comprehensive membrane caps and the presence or absence study and may be affected by pesticides, we of yolk in the nest. Nests in colonies were ob- wished to further investigatereproductive suc- servedmostly from a blind; adult attentiveness cess.In 1973 and 1974 we examined nestsand and activities and nest predation were noted. nestinghabitat and investigated causesof nest Broods and adults were censused weekly loss at Bear River Migratory Bird Refuge. throughout the summer by counting all seen from dike roads. In 1974 regular stops STUDY AREA AND METHODS were made on the outside unit boundaries to Bear River Migratory Bird Refuge is 25 km scanthe far sidesof the refuge impoundments. west of Brigham City, Utah, on the northern Using this method, most of the water area of edge of the Great Salt Lake. Water from the the refuge was covered. Bear and Malad rivers is held in five large We classifiedgrebes as: adults, class 1 young impoundments at the refuge by a system of (on parent’s back), class 2 young (free-swim- dikes and canals.The refuge contains 9,268 ha ming downy young), or class3 young (showing of open water, and 5,811 ha of marsh. The black on the head and neck). Becauseclass 1 marsh most nearly fits the classIV (semiper- young were often concealed under a parent’s manent ponds or lakes), D (brackish), cover wings and back feathers, they were often dif- type 4 (open water or bare soil on 95% of the ficult to count at a distance. Adult birds were wetland area) accordingto the classificationof often known to have young on their backs but Stewart and Kantrud (197 1). Narrowleaf cat- estimating numbers was difficult. Class 3 tail (T~pha augustzjblia),hardstem bulrush birds, especiallyat later stagesof development, (S&pus acutus), alkali bulrushes (Scirpus resemble adults and thus were difficult to clas- americanusand S. paludosus),saltgrass (Dis- sify. Class 2 birds were the most conspicuous tichlis stricta),and pondweed (Potamogeton and thus presented the best estimate as to spp.) are the predominant plants. Water depth trends in breeding numbers and successof in the five refuge units rangesfrom a few cen- nesting.

[661 WESTERN GREBE NESTING 67 ,/-- \ Young remained’ in class 2 for apnroxi- 1200 mately two weeks.By adding the actual counts 1100 fromevery other,&rvey week minus a correc- 1000 1 tion facwose birds that may have been counted twice), we obtained an estimate of class 2 production. The correction factor for a weekly survey was one-seventh of the class 2 total from the survey that preceded by two weeksthe survey being corrected. One-seventh was used becauseif a class2 young were to be counted twice, it would have to become a class 2 on the day of the first week’s survey. We 100 / assumedthat one-seventhofthe young on each \ 0 \ survey were just entering class 2. A weekly April ’ May June ’ July ’ 4 csapt 1 Oct. ’ No”. ’ count thus equaled the actual count minus FIGURE 1. Numbers of adult Western Grebes at Bear one-seventh the actual count of the survey River Migratory Bird Refuge in 1973 and 1974. made two weeks previously. Western Grebes occur in two color phases (Storer 1965). We conducted two surveys in 1973 to determine the percent of the popula- NEST SITE SELECTION tion in each phaseand whether birds bred only Western Grebes at Bear River Refuge built with those of the same phase. Birds were clas- nests in emergent vegetation, in open water, sified as “dark phase” if the black of the crown and on dry land. Nests in emergent vegetation extended below the eye and as “light phase” are typical of Western Grebes (Palmer 1962, if the black of the crown ended at a level above Herman et al. 1969). Dry-land nesting has the eye. Light-phase birds usually have a paler, been reported by Nero (1959) and Nero et al. more dappled color on the back than dark- (1958), who believed it to be the result of the phase birds. Birds were considered paired if loss of emergent vegetation. However, Bear swimming close together with no other birds River Refuge did not lose emergent vegetation nearby. All single birds and birds in flocks during the study period. where pairing was not evident were counted Fifty-four percent of 386 nests were in as unpaired. emergent vegetation (details given in Table 1). Nests were always constructed of materials in

RESULTS AND DISCUSSION ADULT POPULATIONS TABLE 1. Nesting materialsand surroundingvegetation at Western Grebe nests,Bear River Migratory Bird Refuge, Western Grebes arrived at Bear River Refuge 1973-1974. in late March and numbers steadily increased throughout the spring and summer. Survey Non-colony Colony data collected in 1974 indicated an adult pop- nests nests ulation between 11 June and 30 July of about Nesting materials 690 birds. In August and September, numbers Hardstem bulrush 16 92 rose with the inclusion of young in the adult Cattail 4 27 class and the arrival of migrants from other Hardstem bulrush-cattail 5 6 Saltgrass 3 7 areas (Fig. 1). Many birds remained on the Hardstem bulrush-saltgrass 2 1 Refuge until mid-October, after which most Alkali bulrush 2 61 of them departed. By the end of November, Cattail-saltgrass 0 2 a few stragglersremained and occasionally a Sagopondweed 0 158 few remained through the winter. Total 32 354 Twelve percent of the birds (103 of 7 17 Surroundingvegetation birds) were light phaseand the remainder dark Hardstem bulrush 17 phase.Of 16 1 pairs seenon two days, only one Cattail 6 consisted of a light and a dark phase bird. If Hardstem bulrush-cattail 3 2 Saltgrass 7 the birds were mating irrespective of color Sagopondweed : 158 phase, 3 5 of the 16 1 pairs observed would be None 0 5 expected to be dark-light pairs. These results Hardstem bulrush-saltgrass 2 0 agree with Storer’s (1965) finding that the Alkali bulrush 0 60 0 grebes tend strongly to select mates of their Cattail-saltgrass 32 354 own phase. Total 68 MARK L. LINDVALL AND JESSOP B. LOW

TABLE 2. Nest characteristicsof Western Grebesat Bear ling (1964) also suggestedthat Western Grebes River Migratory Bird Refuge, 1973-1974. prefer to nest near or on open water. Nearness to open water could allow for early detection Colony Non-colony Characteristic nests nests of and rapid escapefrom predators. Western Grebes at the Refuge nested singly Mean distance to open water (m) 0.3 0.1 Mean distance to nearest nest (my 10 or in colonies. Colony nests were more easily Mean distance to land (m) 20.5 2 found and thus singlenests (5%) may be under- Mean depth nearestopen water(m) 0.3 0.4 represented. Single nests and their placement Mean nest diameter (m) 0.4 0.5 did not significantly differ from colony nests Adjacent moving water (no.) 87 9 Adjacent stagnantwater (no.) 296 23 in terms of water depth, vegetation from which Floating nests (no.) 119 4 they were constructed, or surrounding vege- Non-floating nests (no.) 83 3 tation. McCartan and Simmons (1956) re- aNon-colony not includedfor this variable ported both colonial and non-colonial nesting for the (Podicepscrista- tus>. the surroundingvegetation. They were located Most (95%) nestswere in colonies number- near open water (average distance 0.4 m) and ing from 5 to 88 nests.The colonieslined chan- built on a snag, or resting on the bottom in nels into the marshesor the edge of dikes with shallow water (76%), or were floating (24%). emergent vegetation, channels without emer- The average distance from land of nestsbuilt gent vegetation, edges of large open-water in emergent vegetation was 55 m (Table 2). areas, and open-water areas devoid of emer- Most nests were conspicuous and easily ob- gents. served. In colonieswith 10 or fewer nests,nests were Nests in open water accounted for 4 1% of spacedan averageof 30 m apart, while colonies the total; they were found in 1973 and 1974 larger than 10 nests averaged 15 m or less. in the same location. These floating raft-like Burger (1974) describeda similar situation for nests were constructed exclusively of pond- the White-tufted (Rollandia rolland) and Sil- weed (Potamogeton spp.) in stagnant water very grebes (Podicepsoccipitalis). with no emergent vegetation. The nests were Egg laying, begun in late May, peaked the about 70 cm acrossand extended 30 cm below first half of July (Fig. 2). Clutches started in the water’s surface. The nest platforms were the peak period 1 to 15 July were a combi- approximately 10 cm above water level at the nation of first nestings and renestings. We edgesand 5 cm in the center. In 1973, Western found evidence of renestingat Bear River Ref- Grebes nested in dense pondweed beds about uge as clutches destroyed by avian predation 0.8 km from shore in 56 cm of water. Nests were replaced. Nero (in Palmer 1962) stated were held in place by the dense mat of pond- that replacement clutches are common in weed surrounding them. In 1974, pondweed Western Grebes. was not so dense as in 1973 and the colony Both male and female grebes shared incu- was located only 200 m from shore in 29 cm bation duties as the members of pairs were of water. Nests in 1974 were smaller (average often seen to replace each other on the nest. diameter 24 cm) and were held in place by The incubation period was 21 to 28 days, av- contact with the bottom, not anchored in or eraging 24 days for 14 clutches for which the surroundedby pondweed. This type of nesting day of first laying and hatching were known. has not previously been reported for Western Bent (19 19) reported incubation to be “about Grebes. 23 days.” The average clutch size for 70 com- Dry-land nestsmade up 5% of the total and plete clutcheswas 2.6 and ranged from one to were made of materials from the surrounding four. Herman et al. (1969) found a modal vegetation. Most dry-land nests were located clutch size of three while Nero (in Palmer near flowing water (89%) and close to open 1962) stated clutches usually numbered three water (average distance to open water was 4 to four. Davis (196 1) found many four-, five-, cm). The average depth of the nearest open and six-eggclutches. Clutches larger than four water was 21 cm. eggs were not incubated and we considered Western Grebes selected nest sites near them dump nests;however, only three of these water more than 20 cm deep. They commonly dump nestswere found. Bent (19 19) and Fin- nested in places where emergent vegetation ley (1907) also reported dump nestsfor West- was sparse or lacking. Of 202 nests found in em Grebes. 1974, only three had overhead cover. This was the only trait consistently shared by all three NESTING SUCCESS nest types. Bent (1919) Wetmore (1924) Although we did not monitor open-water nests Yocum et al. (1958) Davis (196 l), and Stur- for success,the fate of 221 colonial and non- WESTERN GREBE NESTING 69

TABLE 3. Fate of Western Grebe nests at Bear River Migratory Bird Refuge, 1973-1974.

Non- colony Colony Fate nests nests

Successfulnests (some or all eggshatched) 14 33 Avian predation 14 75 Abandoned 1 9 Flooded and destroyedby wave action 1 10 Lost but causeunknown 1 10 Drop in water level and abandoned 0 56 Unknown fate 1 162 FIGURE 2. Nesting activity of Western Grebes at Bear Total 32 355 River Migratory Bird Refuge in 1973 and 1974. colonial nests located in vegetation showed exposingmudflats. Twenty-five percent of the that 2 1% of the clutches hatched at least one grebes subsequently abandoned their nests. young. When disturbed, the grebes did not Burger (1974) reported nest lossesfrom flood- cover their eggs,thus making an already con- ing in the White-tufted and Silvery grebes. spicuousnest even more visible to predators; Flooding caused few lossesat the Refuge due however, the eggswere generally covered when to the relatively stable water levels. Only 5% undisturbed birds left their nests. of the nestswere lost to wave action and flood- Avian predation accounted for 40% of the ing. nest loss (Table 3). American Coots (Fulica Abandonment accounted for a loss of 4% of americana) and California Gulls (Lams cali- the nests monitored. This figure may be low fornicus) were the main nest predators. Egg becauseabandoned nests may have been de- predation was observed three times, two of stroyed by predators before they were checked, which involved human disturbance. Coots thus being counted as lost owing to predation were common in the grebe nesting areas and rather than abandonment. often swam among the grebe nests. In one in- Nests in open water were not monitored for stance,a coot jumped on an untended nest and successbecause of their vulnerability to pre- ate a portion of one of the eggs.Upon returning dation associated with the resulting distur- to its nest, the grebe picked up the broken egg bance. A California Gull nesting colony and and deposited it in the water 2 m from the loafing area were located near an open-water nest. The grebe then left the area and a coot grebe colony in 1973; gulls were responsible attempted to break the remaining egg. Upon for some of the grebe egg losses. returning an hour later the grebe resumed in- cubating the remaining egg. In another case, BROOD PRODUCTION a California Gull made several aerial passes Broods were reared in large open-water areas at a grebe nest before removing an egg, which and ditches. The young were fed until they it then dropped on the ground a few meters were almost adult size (four to five weeks). from the nest. After 7 to 10 days of age, young beganto spend Yocum et al. (1958) found evidence of egg more time off the backs of parents. However, predation on Western Grebe nests by Ring- young remained near the parent birds and billed Gulls (Lams delawarensis). McCartan climbed on the back ofa parent when alarmed. and Simmons (1956) observed predation of Young Western Grebes can be classifiedas Great Crested Grebe nestsby European Coots to color phase.Dark-phase young began show- (Fulica atra). We believe that some form of ing black on the head, neck, and back at 12 disturbanceallows predation as we saw West- days of age. Light-phase young did not show em Grebes defend their nests against both black on the head, neck or back until after five coots and gulls. Disturbance from human ac- or more weeks. At 25 to 35 days of age, the tivity suchas cars,planes, or helicopterssome- young resembled the adults in size, plumage, times causedbirds in the Refuge to leave their and color phase. nests and swim about the colony. Birds also The first young were seen on 1 June 1973 left their nestsfor short periods to chaseother and on 28 May 1974, indicating that some Western Grebes from the nesting area and to birds began pairing and breeding during May, add vegetation to their nests. On rare occa- before most of the birds arrived on the nesting sions, they left their nests for several hours. grounds. Brood rearing reached a peak in late The (uncontrolled) water level at one large July (Fig. 3). The peak counts for class2 young colony dropped 38 cm in lessthan three weeks, were in August. The last class 1 young were 70 MARK L. LINDVALL AND JESSOP B. LOW

160 , A Specialthanks for field supervisionand manuscriptreview 160 \ are given to John Kadlec, David Capen, Lloyd Gunther, 1 Wayne I. Jensen,and Robert R. Selander.

- 1973 LITERATURE CITED ----- ,974 BENT, A. C. 1919. Life histories of North American div- inn birds. U.S. Natl. Mus. Bull. 107. BURG& J. 1974. Determinants of colony and nest-site selectionin the Silver Grebe (Podicepsoccipitalis) and Rolland’s Grebe (Rollandia rolland). Condor 76:301-306. \ DAVIS, D. G. 1961. Western Grebe colonies in northern Colorado. Condor 63:265-266. June July Sept. Oct. Nov. May Aug. FINLEY, W. L. 1907. The grebes of southern Oregon. Condor 9:97-101. FIGURE 3. Western Grebe young at Bear River Migra- HERMAN,S. G., R. L. GARRETT,AND R. L. RUDD. 1969. tory Bird Refuge in 1973 and 1974. Pesticidesand the Western Grebe, p. 24-55. In M. W. Miller and G. G. Berg [eds.], Chemical fallout. Charles C Thomas. Springfield, IL. seen in late September. The fate of young LINDVALL,M. L., AND j. 6. Low. i979. Organochlorine hatched this late was unknown. Occasionally and PCB residuesin Western Grebes from Bear River a few Western Grebes were icebound in late Migratory Bird Refuge,Utah. Bull. Environ. Contam. fall. Toxicol. 22~754-766 LINDVALL.M. L.. AND J. B. Low. 1980. Effects of DDE. In 1973, 158 class 2 young were produced TDE,‘and P&s on shell thicknessof Western Grebe and in 1974, 269. Several indices to repro- eggs, Bear River Migratory Bird Refuge, Utah ductive successwere computed. One was the 1973-1974. Pestic. Monit. J. 14:108-l 11. number of young per adult. Total class2 young MCCARTAN,L., AND K. E. L. SIMMONS. 1956. Territory in the Great Crested Grebe Podicepscristatus re-ex- produced and the number of adults present at amined. Ibis 98370-378. breeding time gave an index of 0.3 5 young per NERO, R. W. 1959. Western Grebe colony. Nat. Hist. adult. Another indicator of successwas the 68:291-295. average class2 brood size per mated pair: this NERO,R. W., F. W. LAHRMAN,AND F. G. BARD. 1958. was 1.7. Rudd and Herman (1972) found 1.7 Dry land nest site of a Western Grebe colony. Auk 751347-349. young per mated pair in what they considered PALMER,R. S. [ED.] 1962. Handbook of North American a normally reproducing population. In the birds. Vol. 1. Yale Univ. Press, New Haven, CT. population at Clear Lake, California, where RIJDD,R. L., AND S. G. HERMAN. 1972. Ecosystemtrans- Rudd and Herman (1972) believed DDD to feral of pesticideresidues in an aquatic environment, p. 471485. In F. Matsumura, G. Bonsh, and T. be affecting reproduction, 1.O young per mated Misato [eds.], Toxic effect of pesticide residues on pair was found. wildlife. Environmental toxicology of pesticides.Ac- In most respectsthe nesting habits of West- ademic Press, New York. ern Grebes at Bear River Refuge are similar STEWART,R. E., AND H. A. KANTRUD. 1971. Classifi- to those of populations studied elsewhere. cation of natural ponds and lakes in the glaciated prairie region. U.S. Bur. Sport Fish. Wildl. Resour. Nesting in areas with no emergent vegetation Publ. 95. and non-colony nestshave not been previously STORER,R. W. 1965. The color phasesof the Western reported. Western Grebes at Bear River Ref- Grebe. Living Bird 4:59-63. uge have fairly high pesticide and PCB levels STURLING,D. 1964. Western Grebe colony on Shurway Lake revisited. Murrelet 45:8-9. (Lindvall and Low 1979, 1980) but appear to WETMORE,A. 1924. Food and economic relations of be reproducing normally as compared to those North American grebes.U.S. Dep. Agric. Bull. 1196. studied by Rudd and Herman (1972). Avian YOCUM, C. F., S. W. HARRIS,AND H. A. HANSEN. 1958. predation caused the greatest losses but re- Statusof grebesof easternWashington. Auk 75:3647. nesting may have lessenedits impact. U.S. Fish and Wildlif Service, Target Rock National ACKNOWLEDGMENTS Wildrife Refuge,Box 533, Huntington, New York 11743. Addressof secondauthor: Utah CooperativeWildrife Re- This project was funded primarily by the U.S. Fish and search Unit, College of Natural Resources,Utah State Wildlife Service through the Utah Cooperative Wildlife University,Logan, Utah 84322. Accepted for publication ResearchUnit. Funding was alsoprovided by The Wildlife 8 March 1980. Society and the Ecology Center, Utah State University.