Nesting Ecology of the Double-Crested Cormorant (Phalacrocorax Auritus Auritus) on Utah Lake

Brigham Young University BYU ScholarsArchive

Theses and Dissertations

1974-04-01

Nesting ecology of the double-crested cormorant (Phalacrocorax auritus auritus) on Utah Lake

Ronald M. Mitchell Brigham Young University - Provo

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BYU ScholarsArchive Citation Mitchell, Ronald M., "Nesting ecology of the double-crested cormorant (Phalacrocorax auritus auritus) on Utah Lake" (1974). Theses and Dissertations. 7826. https://scholarsarchive.byu.edu/etd/7826

This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. NESTING ECOLOGYOF THE DOUBLE-CRESTED

CORMORANT(PHALACROCORAX AURITUS

AURITUS) ON UTAH LAKE

A Thesis Presented to the Department of zoology Brigham Young University

In Partial Fulfillment of the Requirements for the Degree Master of science

Ronald M. Mitchell April 1974 ACKNOWLEDGMENTS

I would like to thank the members of my committee, Dr. Joseph R. Murphy and Dr. Joseph R. Murdock, for their critique of this manuscript and their help in research and writing. I owe a special debt of gratitude to Dr. Herbert H. Frost for suggesting the problem and for his encouragement and direction during my research and manuscript preparation. I would like to thank Dr. Stephen Wood for identifying the invertebrates found in the nests. I want to thank Don Karr and his staff for their cooperation in providing equipment and supplies from the Zoology Department. Special thanks must go to Mr. Blaine Cropper and the employees at Geneva Steel for their friendly acceptance and for allowing me to conduct research on their property. Thanks also to Randy Isham, fellow student and friend who aided me on several occasions in research that I could not do alone. I would like to express special appreciation to my wife, Mimi, for her understanding and encouragement. I am grateful for her suggestions during formulation of the thesis and for typing the rough draft.

iii TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS• • • • • • • • • • • • • • • • • • • • iii LIST OF TABLES • • • . • • • • • • • • • • • • • • . • vi LIST OF ILLUSTRATIONS . • • • • • • • • • • . • . • • . viii INTROD'C.X!TION• • • • • • • • • • • • • • • • • • • • • 1 Review of the Literature • • • • • • • • • • • • • 3 THE STUDYAREA • • • • • • • • • • • • • • • • • • • • 10 METHODSAND PROCEDURES • • • • • • • • • • • • • • • • 19 RESULTS • • • • • • • • • • • • • . • • • • • • • • • • 24 Earliest Observation • • • • • • • • • • • • • . • 24 Courtship and Nest-building • • • • • . • • • • • 24 Nests • • • • . • • • • • • • • • . • • • • • • • 25 Egg-laying • • • • . • • • • . • • • • • • . • . • 29 Clutch Size • • • • • • • • • • • • • • • • • • • • 29 Egg Measurements • • • • • • • • • • • • • • • • . 30 Hatching • • • • • • • • • • • • • • • • • • • • • 30 Measurements of the Young • • • • • • • • • • • • • 33 Food Items • • • . • • • • • • • • • • • • • • . • 39 Reaction to Human Handling • • • • • • • • • • • • 39 Banding • • • • • • • • • • • • • • • • • • • • • • 39 Leaving the Nest • • • • • • • • • • • • • • • • • 39 Departure Dates • • • • • • • • • • • • • • • • • • 41 DISCUSSION • • • • • • • • • • • • • • • • • • • • • • 42

iv Page

A New Record • • • • • • • • • • • • • • • • • • • 42 A New Colony • • • • • • • • • • • • • • • • • • • 42 Utah's Cormorant Population • • • • • • • • • • • • 43 Arrival Dates • • • • • • • • • • • • • • • • • • • 46 courtship and Nest-building • • • • • • • • • • • • 47 Nests • • • • • • • • • • • • • • • • • • • • • • • 49 Egg-Laying and Incubation • • • • • • • • • • • • • 55 Clutch size • • • • • • • • • • • • • • • • • • • • 59 Egg Measurements • • • • • • • • • • • • • • • • • 59 Egg Volumes • • • • • • • • • • • • • • • • • • • • 62 Hatching • • • • • • • • • • • • • • • • • • • • • 65 Predation Of Eggs and Young • • • • • • • • • • • • 69 Measurements of the Young • • • • • • • • • • • • • 71 Development of the Young • • • • • • • • • • • • • 73 Food Items • • • • • • • • • • • • • • • • • • • • 74 Banding • • • • • • • • • • • • • • • • • • • • • • 78 Leaving the Nest • • • • • • • • • • • • • • • • • 79 Departure Dates • • • • • • • • • • • • • • • • • • 81 Subspecific Status • . • • • • • • . • • • • • • • 82 Effects of Diking Provo Bay • • • • • • • • • • • • 86 SUMMARY• • .. • • • • • • • • • • • • • • • • • • • • • 88 REFERENCES CITED • • • • • • • • • • • • • • • • • • • 90 ADDITIONAL REFERENCES • • • • • • • • • • • • • • • • • 98

V LIST OF TABLES

Table Page 1. Number of nests built in each tree at Geneva colony, with the percent of the total colony nests in parenthesis • • • • • • • • • 26 2. Numbers of eggs laid per nest at the Utah Lake Colonies ••••••••••••• • • • 30 3. Egg measurements from Utah Lake, showing range in length and width measurements with averages in parentheses • • • • • • • • • • • 31 4. Summary of the nests selected for study at the Springville colony, in 1973. • • • • • • • • 32 5. Summary of the nests studied at the Bay colony, in 1973. • • • • • • • • • • • • • • • • • • 33 6. Summary of the nests selected for study at the Geneva colony in 1972 • • • • • • • • • • • • 34 7. Summary of the nests studied at the Geneva colony, in 1973 • • • • • • • • • • • • • • • 35 8. Reactions to human handling by Double-crested Cormorant nestlings during specific age periods • • • • • • • • • • • • • • • • • • • 40 9. Average length and width measurements of all eggs measured in 1972 and 1973, compared to random samples of one egg from each of twelve clutches. • • • • • • • • • • • • • • 61 10. Volumes of eggs collected in 1972, from Geneva, showing variation of averages nearest width compared to averages nearest length. • • • • 63 11. Volumes of eggs collected in 1973, from Geneva, showing variation of averages nearest width compared to averages nearest length. • • • • 64 12. A random selection of 20 eggs, taken at different times and from different locations, showing the volume as figured by length and width measurement compared to volume computed fro1.t weight • • • • • • • • • • • • • • • • • • • 66 vi Table Page 13. Numbers of active nests in the Utah Lake colonies over a four-year period ••• • • • 77

vii LIST OF FIGURES

Figure Page 1. Location of the deserted and active nesting colonies in Utah •••••••••••• • • 6 2. Location of the three study sites on Utah Lake • • • • • • • • • • • • • • • • • • • • 8 3. Springville colony as viewed from the south • • 11 4. Bay colony as viewed from the south. • • • • • 14 5. Map of Geneva reservoir showing the location of the blinds and the trees containing cormorant nests ••• • • • • • • • • • • • • 16 6. Geneva colony as viewed from the east. • • • • 17 7. Geneva cormorant nest with an incomplete clutch of eggs • • • • • • • • • • • • • • • 28 8. Average daily increase in weight showing range of daily measurements. • • • • • • • • • • • 36 9. Average daily increase in beak length showing range of daily measurements. • • • • • • • • 37 10. Average daily increase in tarsometatarsal length showing range of daily measurements • 38 11. Cormorants at Bear River Refuge utilizing a ground-nesting environment ••••••• • • 45 12. Distribution of nest height, showing hatching success above and below the average nest height • • • • • • • • • • • • • • • • • • • 52 13. Distribution of egg laying at Geneva colony from 14 April to 20 May 1973. • • • • • • • • • • 57 14. Distribution of egg hatching at Geneva colony from 19 May to June 1973 • • • • • • • • • • 68 15. Geneva fledglings that are approximately 24 days old. • • • • • • • • • • • • • • • • 75

viii INTRODUCTION

The cormorant has never been considered a "romantic" bird by researchers, or one which attracts large numbers of eager scientists for detailed studies. concerning the cormorant, Townsend (Bent 1922) writesa A populous colony ••• presents a most interesting, if not attractive picture. Such a colony is the filthiest place imaginable, for no other birds can equal the cormorants in this respect. The nests and their surroundings become thoroughly white-washed with excrement, ••• swarming with flies; the nests are often alive with fleas, lice, and other vermin; and the odor of decaying fish ••• adds to the nauseating stench. An ornithologist studying birds in Quebec (Demille 1926) cited the attitude of a local citizen towards cormorants, "God no doubt had his reasons for creating each living thing, but when he made the cormorant, he did him- self little credit." These conditions and attitudes have resulted in a lack of scientific data concerning the cormorant and severe reductions in their populations in North America. Concern for the cormorants• impact on commercial fishing initiated two detailed studies (Lewis 1929; Mendall 1936) of the Double-crested Cormorant (Phalacrocorax auritus auritus), nesting along the Atlantic coast. Although there are three other subspecies (f. ~• albociliatus; P. E• floridanus; P.a. cincinatus) found in North America, p. E• auritu~ is

1 2 considered the most important, due to its wide distribution. Even though f• ~• auritus ranges from the Atlantic coast to Utah, and from certral Canada to Texas, there is limited information concerning those birds found nesting inland. The subspecific status of the cormorants found in Utah was disputed for some time. The fourth edition of the A.o.u. Check-list (1931) reported that they belonged to the subspecies, f• ~• albociliatus, while Lewis (1929) and Peters (1931) designated them as f• ~• auritus. On the basis of plumage and wing measurements, Behle (1936; 1941) identified them as f• ~• auritus, but felt they were intermediate between the two subspecies. Very few published references exist concerning the nesting of the Double-crested Cormorant in Utah (Behle 1958) and Utah Lake is mentioned once in the literature as a "former" nesting site {Woodbury et al. 1949). Bee (1920) collected eggs from a cormorant nest on Provo Bay, in 1920, and Cottam {1927) stated in an unpublished master's thesis that the Double-crested Cormorant nested on Utah Lake. Dr. Herbert H. Frost informed me in 1971 that there were cormorant colonies located around Utah Lake, but no information was available concerning them. Provo Bay is an excellent nesting area for cormorants since there are a number of trees growing in shallow water, which is their preferred nesting habitat. The projected plan of the Bureau of Reclamation (U.S. Department of Interior) to dike and drain Provo Bay as part of the 3 Central Utah Project would eliminate two of the present nesting sites. Another nesting colony of cormorants is in trees located on a dike in the reservoir of the Geneva Steel Works, west of Orem. This area is unusual because of the large numbers of California gulls that nest near the cormorants, the proximity of human activity, and the large amounts of industrial wastes present in the air and water. The purpose of this study was to gather information to help determine the ecological role of the Double-crested Cormorants nesting on Utah Lake and the effects of the possible destruction of their present nesting sites. In order to appreciate the impact the destruction of these nesting sites might have, it was necessary to conduct a census of all cormorant nesting colonies in the state. Furthermore, since the Geneva colony would not be affected by the diking, comparisons were made between the colonies to determine any significant differences in nesting, hatching success, etc.

Review of the Literature

The Double-crested Cormorant has been found nesting or as a winter resident in Canada, Cuba, Bermuda, and every U.S. state, except Hawaii. The subspecies, p.a. auritus is the most widely distributed, with breeding colonies reported in Alberta (L~wis 1929); Manitoba (Bent 1922; Munro 1927; Lewis 1929; Cartwright 1931); New Brunswick (Lewis 1929); Newfoundland (Griscom 1926; Lewis 1929); Nova Scotia (Bayley 4 1925; Lewis 1929); Ontario (Fargo and Van Tyne 1927; Snyder 1928; Lewis 1929); Prince Edward Island (Peters 1942); Quebec (Bryant 1861; Taverner 1915; Townsend 1920; Bent 1922; Stoddard 1923; Lewis 1929); Saskatchewan (Mcinnes 1913; Mitchell 1925; Lewis 1929); Arkansas (Howell 1911; Sutton 1967); Colorado (Bailey and Niedrack 1937); Idaho (Palmer 1962); Illinois (Barnes 1890; Smith 1911; Musselman 1932); Indiana (Hicks 1934; Perkins 1935); Iowa (DuMont 1934; Hunter 1936); Kansas (Tordoff 1956; Johnston 1965); Louisiana (Oberholser 1938); Maine (Norton and Allen 1931; Berolzheimer 1932; Cruickshank 1938); Massachusetts (Hagar 1941); Michigan (Van Tyne 1937; A.O.U. 1957); Minnesota (Uhler 1925; Lewis 1929); Montana (Marsh 1934); Nebraska (Lewis 1931); New York (Kutz 1947; Palmer 1962); North Dakota (Uhler 1925; Lewis 1931); Ohio (Bent 1922}; Oklahoma (Sutton 1967); Rhode Island (Mackay 1894); South Dakota (Lewis 1929; Lundquist 1932; Youngworth 1932); Tennessee (Ganier 1932; 1933}; Wisconsin (Stoddard 1922); and Wyoming (Skinner 1929), There remains some question whether this subspecies nests in New Mexico (Monson 1946; A.o.u. 1957; Palmer 1962; Ligon 1961); and Texas (Stephenson 1942; Wolfe 1956; A.O.U. 1957; Palmer 1962; Sutton 1967). They are occasionally found wintering in Cuba and Bermuda (Palmer 1962). The first reference to a breeding colony of cormorants in Utah was made by Stansbury ( 1852), who discov~red them nesting on Egg Island in the Great Salt Lake, on 19 April 1850. This colony was extensively studied by Behle 5 (1958) and others until 1947. Behle (personal communication) stated that the Egg Island colony has since been abandoned because of human disturbance (fig. 1). Another colony consisting of 75 pairs of birds was reported to exist on Dolphin Island, Great Salt Lake, by Treganza (Lewis 1929). This colony, sighted in 1919, has not been recorded as a nesting site since that time. A colony of 40 nests, which had been destroyed by humans at the time of the visit, was reported in trees, around Bass Pond Reservoir (Clear Lake) in Millard County (Pearson 1927). A large colony was reported at Bear Lake by Treganza (Lewis 1929) in 1919 and estimated at four hundred birds. c. Lynn Hayward reported 118 nests there in June 1928, and 200 nests in May 1929 (Behle 1935). The colony was abandoned soon afterward, according to Hayward (personal communication), due to low lake levels and human disturbance. Cormorants are reported to have nested with Great Blue Herons in trees along the Little Bear River, five miles west of Logan (Stanford 1937). This colony was visited in 1936 and 1937, although no mention is made as to numbers of birds or nests. Hayward visited there on 13 May 1938 (Bee and Hutchings 1942). Eggs were collected from cormorant nests at the colony in 1949 (Payton 1949), but apparently the area was deserted a few years later. When piles of rocks were placed on islands constructed at Bear River National Wildlife Refuge, Box Elder 6

Bear Lake N &· LOgan

• Brigham . Ogden UTAH

. Bountiful ·salt Lake

Tooele

. vernal Utah Lake

· Nephi . Price

Clear Lake i -Fillmore

·Moab

& Deserted or destroyed colonies • Present active colonies

. Cedar City

· st. George -Kanab

FIGURE 1. Location of the deserted and active nesting c~lo- nies in Utah (map by author). 7 county, cormorants are reported to have nested there for the first time in 1936 (Marshall 1937). However, Wetmore (1915) collected young from a cormorant nest at the mouth of Bear River in 1915. Behle (1958) included a table which showed continuous usage through 1949. Behle (1958) reported a pair of cormorants nested for the first time at Farmington Bay State Bird Refuge, Davis County, in 1951, on an island in the south unit. However, Bee (1935) stated that a few cormorants nested on an island in the Jordan River on land belonging to the Jordan Fur and Reclamation Company in 1935. Part of that land now belongs to the state refuge at Farmington Bay. Other references include Hayward's statement that a set of Double-crested Cormorant eggs were taken on 10 May 1901, from White Rock by Harry Aldous (Woodbury et al. 1949). White Rock is a small island located a few hundred yards northwest of Antelope Island, Great Salt Lake. Bee (1920) collected four eggs from a cormorant nest in Provo Bay in 1920. In 1937, John Hutchings of Lehi (Bee 1937) reported that several sets of Double-crested Cormorant eggs were collected on Rock Island in Utah Lake (fig. 2). James Bee (1946) found six cormorant nests, each containing eggs, in a tree on the Geneva dike in May 1946, and stated that the birds had nested there for two or three years. Bee (1949) reported a trip to a large cormorant rookery in Provo Bay, south of the airport dik,, that contained 150 pairs of nesting birds. According to Hayward (personal communication), N 8

Geneva steel Utah Works

Lake

Proposed Dike---

GOSHEN BAY Springville colony Bay colony e Geneva colony

FIGURE 2. Location of the three study sites on Utah Lake (map by author). 9 this colony was reduced in size in the late 1950•s, because of the high water levels that killed some trees. A smaller colony was reported in this same area in 1959 and through the early 1960•s. This colony was again reduced in size due to rotting trees and increased boating action during the late 1960•s. THE STUDYAREA

There are three nesting colonies of Double-crested Cormorants located near Utah Lake. All three were included in this study to obtain comparisons and gain a total picture of the birds' impact on the area. Two of the colonies are located in Provo Bay {fig. 2), which is a shallow area on the eastern side of Utah Lake. These have been designated as the Springville and Bay colonies. The bay is located directly south of the Provo airport and extends east to the I-15 freeway and then south for about 5 km. The water depth in this area varies from a few millimeters to 2 m and averages about 1 m. The principle vegetative type are hardstern bullrush {Scirpus acutus), tamarix {Tamarix petandra), and occasional cottonwood (Populus fremonti) and willow (Salix amygdaloides) trees. Spanish Fork River and Hobble Creek, as well as numerous natural springs, provide water to the area. Irrigation water from agricultural use also drains into the bay. Effluent from the Provo waste-water treatment plant also drains into the area. The third colony is located

11 km north of Provo Bay, at the United States Steel Company's Geneva plant and is designated Geneva colony. The Springville colony is located .5 km due west of the mouth of Hobble Creek in a group of cottonwood trees that range from 10-15 min height (fig. 3). They extend in a straight line west from the shore into the bay. The tree 10 11

FIGURE 3. Springville colony as viewed from the south. 12 line, which is about .5 km long, was established in the late 1930•s during low lake levels. The most western of these trees are dead and standing in 1 m of water. This is the preferred nesting habitat of the cormorant. In 1971 and 1972, the last ten trees in this group were used by cormorants for nesting. In 1973, apparently due to increased numbers, the birds moved eastward into some living cottonwoods that had been exclusively used by Great Blue Herons (Ardea herodias) for nesting. There were two Great Blue Heron nests located in the dead trees above the cormorants• nests. Thirty-six other heron nests were located in the living cottonwoods at the east end of the colony. Their hatching began in April and continued through May. Large numbers of young were observed during the study. A Mallard (~ platyrhynchos) nest with six eggs, a Tree swallow (Iridoprocne bicolor) nest, and two Magpie (Pica pica) nests were also located in these same trees. During the spring, large numbers of Canada Geese (Branta canadensis), Pintails (~ acuta), Cinnamon Teal (~ cyanoptera), Mallards, American Widgeons (Mareca americana), Shovelers (Spatula cly:peata), Canvasbacks (Aythya valisineria), Redheads (Aythya americana), and American Coots (Fulica americana) were seen feeding in the area around the trees. White-faced Ibis (Plegadis chihi), Black-crowned Night Herons (Nycticorax nycticorax), and Snowy Egrets (Leucophon thula) were observed feeding during the spring and summer months in shallow areas. White Pelicans (Pelecanus erythrorhynchos) were often seen 13 feeding a few hundred meters southwest of the colony. Musk- rats (Ondatra zibethica) and three of their dens were observed in bullrushes near the colony. There was little human disturbance in the actual nesting area since the only access was by wading or paddling a canoe. Dr. Clayton M. White and three students obtained 10 eggs from 10 different cormorant nests in 1973, for a study on DDT content. However, these nests were not included in the field study, so they did not influence results. The Bay colony is located at the mouth of Provo bay (fig. 2), 2 km due south of the Provo airport. This site consists of a group of cottonwood and willow trees growing in an east-west line in about .6 m of water (fig. 4). In 1971, the area comprised 18 trees ranging from 9-15 min height. Within two years (1971-1972), four of these trees were lost for nesting purposes after being blown over in storms. In 1973, cormorants nested in one cottonwood and in four willow trees at the east end of the tree line. In 1971 and 1972, they also nested in cottonwood trees further west. There were 28 nests of the Great Blue Heron located in this area, some in the same trees as the cormorants, but at higher levels. American Coot and Yellowheaded Blackbird {Xantho- cephalus. xanthocephalus) nests were found in the bullrushes near the trees. During the spring, large numbers of Western Grebes (Aechmophorus occidentalis), Pintails, Cinnamon Teal, and Mallards were seen feeding near the colony. A large colony of Black-crowned Night Herons and snowy Egrets was 14

FIGURE 4. Bay colony as viewed from the south. 15 located 200 m north of the colony and they were often seen in the area. A Canada goose nest with eight young was found near the colony in April. One Marsh Hawk (Circus cyaneus) and numerous California Gulls (Larus californicus), Long- billed Marsh Wrens (Telmatodytes palustris), Tree swallows, and Bank swallows (Riparia riparia) were seen flying near the nesting area. One muskrat was seen near the colony. Due to the shallow water, there is little disturbance from boating in this area. However, we saw evidence that people did tie up boats under the trees and fish there. This may have caused considerable problems for the nesting birds. The Geneva colony is located on a diversion dike built in 1940, that extends about 1.2 km within the reservoir (fig. 5). This artificial lake is located west of the steel plant proper and is about .2 km from Utah Lake. The water is contained by 3 m high, earthen walls. It was necessary to obtain permission to enter since the reservoir is on property, owned by u.s. Steel. The pond is irregularly shaped and measures about 1 km on the south end, 2.4 km on the east and west side, and .3 km on the north side. The water, which is over 6 m deep in most places, is used for cooling purposes in the steel-making process. The cormorants nested in one cottonwood and three Siberian Elm. (Ulmus pumila) trees, all living, at the distal end of the dike (fig. 6). One of these trees also contained two Great Blue Heron nests. Thousands of California Gulls nested on the dike from March to June. On 8 June 1973, there were 8 16

N .3 km 1

ridge

__ Retaining Walls

1 km

• Tree 1 .. Tree 3

Tree 2 • Tree 4

FIGURE 5. Map of Geneva reservoir showing the location of the blinds and the trees containing cormorant nests (map by author). 17

------

FIGURE 6. Geneva colony as viewed from the east. 18 Black-crowned Night Heron and 39 Snowy Egret nests, both containing eggs and young, located in Tama.rue, Black Mull- berry (Morus nigra), Siberian Elm, and Cottonwood trees on the main dike. Cinnamon Teal, Redheads, and American coots were seen feeding on the pond with their young. Magpies, Red-winged Blackbirds (Agelaius phoenecius), House Sparrows (Passer domesticus), and Forster's Terns(Sterna forsteri) were occasionally seen flying near the dike. Several Striped Skunks (Mephitis mephitis) were observed foraging on the dike, and they continually preyed on the California Gulls' nests. Goldfish (Carassius auratus), which had been planted in the reservoir, were often seen schooling in the clear waters. Human disturbance was controlled since it was necessary to be admitted by a guard before being allowed on the dike. Travel on the dike by employees was minimal and further discouragement was provided by the high concentration of California Gulls. METHODSAND PROCEDURES

The study was commenced during the spring of 1972, and continued in the spring and summer of 1973. TWo blinds, which had been constructed for a previous study, were set up at Geneva colony to allow observation of courtship behavior and nesting activity. The blinds were constructed of 1.3 m square, wooden platforms that could be positioned at various heights by placing 2m-long steel con- duit pipes through each corner and securing with U-bolts. The frame was covered by a piece of green canvas 1.3 m square and 1.8 m high. One corner of the canvas was left unsewn to allow access to the blind. A metal chair was placed in each blind. After the blinds were set up, holes were cut in the canvas in order to observe and photograph the birds. The platform was positioned about 1 m above the ground, which increased visibility of the nests and still allowed considerable headroom in the blind when seated. The blinds were placed in position before the birds returned to prevent disturbance of nesting activities. Both blinds were set up on the east bank of the Geneva pond. One blind was placed opposite trees 1 and 2 about 12 m distant (fig. 5). Six cormorant nests, two Great Blue Heron nests and numerous California Gull, Snowy Egret, and Black-crowned Night Heron nests were visible from this

19 20 blind. Tree 3, which contained three cormorant nests, was also observable using binoculars. The second blind was placed about 300 m farther north, near the north-east corner of the pond. Tree 4 was about 30 m away, and nine cormorant nests, one Great Blue Heron nest, and numerous California Gull and Snowy Egret nests were observable using binoculars or a spotting scope. Seven active cormorant nests at the Bay colony and 33 active nests at the Springville colony were selected for weekly observations of eggs and young. Access to the Bay colony was gained by a motor-powered duck boat launched from the Provo boat harbor. In order to get to the Springville colony it was necessary to use chest-waders or paddle out in a small inflatable kayak. The Geneva colony consisted of 17 active nests which were used for daily observations of eggs and young. Access to the Geneva colony was gained by a l km walk along the primary dike. Due to the excellent visibility of the nests, all trees were mapped and each nest assigned an identification number. The nests which were still intact from the previous year were mapped before the birds returned to determine use of old nests and how many new ones were built. Observations of the eggs and young in the nests were made using four aluminum poles, 1.5 cm in diameter and 1.6 m long, which could be inserted into one another and secured by a wing nut. A side-view mirror attached to the end pole afforded a view of the nest. When held at chest level, a viewing range of 21 8 m allowed visual access to most nests. Tape was placed at .3 m intervals on the poles to measure nest height from ground or water level. A steel tape was used to measure the width of the individual nests. Two nests, one new and the other rebuilt, were collected from the Springville colony for faunal examination in Berlese funnels and comparative measurements of numbers, average thickness, and length of each piece of nesting material. Invertebrates found in the nests were collected for identification. Egg length and width were measured using dial cali- pers accurate to one-twentieth (.05) of a millimeter. Mea- surements were made to compare eggs of the same clutch, eggs within the colony, and for comparison between the Geneva and Springville colonies. Egg volume was determined using the 2 formula, V = 0.526 LB , where L = longitudinal axis and B = transverse axis (Romanoff and Romanoff 1949). Average clutch size was determined for each colony by including abandoned nests, but not unused nests. A nest was considered abandoned if it contained at least one egg at any time, but showed no signs of incubation for one week. Nests that never contained an egg were considered unused. Hatching success for each breeding pair was determined by dividing the number of hatchlings that survived one day, by the total number of eggs laid in the nest; and for the colony by the total number of hatchlings that survived one day, by the total number of eggs laid in the colony. Fletchling success was determined for the GenPva colony by dividing the total number of fledglings which left 22 the nest by the number of hatchlings which survived one day. Three rneasurements--weight, length of bill and tarsometatarsus--were made daily of the Geneva hatchlings to determine growth rates. A number was written on ye11ow tape and attached to the leg of each bird for identification. Weight was measured using three Sargent-Welch, dial spring- balances. The 250 gm balance was accurate to 2 gm, the 500 gm balance to 5 gm, and the 2000 gm balance to 10 gm. A small bag was attached to the balance hook to hold the bird steady for accurate readings. The bill and tarsometatarsus length were measured with a clear plastic 150 mm rule. The bill was measured from the corner of the mouth to the tip of the upper mandible. The tarsometatarsus was measured from the point of articulation below the ankle to its articulation with the middle toe. u.s. Bureau of Sport Fisheries and Wildlife aluminum. bands were placed on the right leg of all nestlings caught during 1972 and 1973. Some food items were found in the nests, and others were obtained when the young birds became agitated and regurgitated their meals. In 1973, trips were made to all recorded nesting sites in the state to determine which colonies still existed and to conduct a census of Utah• s cormorant popul.ation. The colony at Bear River Migratory Bird Refuge was visited to photograph the utilization of an alternative nesting habitat 23 and to determine the present size of the colony. An unreported colony at the Newstate Gun Club, near Bountiful, was visited to determine location and size. Letters were also sent to managers of selected state bird refuges in an attempt to discover new breeding colonies. RESULTS

Earliest Observation

In 1972, the first birds to return to the Springville colony were seen on 4 March. Cormorants were first seen at the Bay colony on 13 March, and at the Geneva colony on 22 March. In 1973, the first cormorants were seen at the Springville colony on 7 March, and on 14 March at the Bay colony. Three birds, seen on 26 March, were the first to arrive at the Geneva colony.

Courtship and Nest-building

In 1973 courtship began in the colonies a few days after tbe first birds had returned. It was difficult to tell the sexes apart visually, but sex was sometimes dis- cernible by watching behavior. The male bird can be identified because they return to the nest area first and display on the nest (Palmer 1962; van Tets 1965). The first males to return would claim the nests that were still in good condition, from the previous year, and that were highest in the tree. They would then use the nest for an advertising display termed "wing-waving" (van Tets 1965), which I observed at Geneva. Threat, recognition, and nest-worrying displays (van Tets 1965) were also seen at the Geneva and Springville colonies. After the pair-bonding was COJD.t:>leted, nests were improved on or built by both sexes. 24 25 Nests Of the 83 cormorant nests located in the Springville colony in 1973, there were 14 nests left from the previous year, that were utilized by the first returning birds. In the entire colony, only five nests were destroyed and two were abandoned. The height of the nests varied from 2.4 m to 7.6 m, from the surface of the water, with an average of 5.2 m. The least number of nests located in a tree was 1, and the most was 11. There did not seem to be any correla- tion between the size of the tree and the number of nests the tree contained. Nests were still being constructed in the eastern part of the colony during late May•. All seven cormorant nests at the Bay colony were used for weekly observation. None were lost during the study, but two nests were abandoned. The nest height varied from 4.3 m to 6.4 m, with an average of 5.3 m. The greatest number of nests located in a single tree was three, and the fewest, one. All nest-building ceased by early April. In 1972 cormorants used four trees on the dike for ·nesting at the Geneva colony. Trees 2, 3, and 4 were all being utilized by 1 April, but tree 1 was not used for nesting until about 10 days later (fig. 5). Nineteen nests that had been left over from the previous year were used, although some were in very poor condition. one old nest in tree 1 was not used, although it seemed in good condition. No nests were abandoned. A total of 14 new nests were built, ranging from none built in tree 1, to 9 new nests in tree 4. One 26 nest each in trees 2 and 4 were lost when they fell out of the trees during a storm. Table 1 shows the number of nests located in each tree and the percent of the total colony nests each tree contained. No measurements of nest height were made in 1972.

TABLE 1. Number of nests built in each tree at Geneva colony, with the percent of the total colony nests in parentheses •

Year Tree 1 Tree 2 Tree 3 Tree 4

1972 4 (13) 9 (28) 6 (19) 14 (40)

1973 3 {18) 2 ( 12) 3 (18) 9 (53)

The same trees used for nesting in 1972 were occupied in 1973. However, tree 1 was utilized first in 1973, followed by trees 2 and 4, and finally by tree 3. Twenty- four nests remained of the 33 used in 1972. some of these were in very poor condition and only 11 of them were reused for ·nesting. No new nests were built in tree 1, and 2 each were built in trees 2, 3, and 4, for a total of 6 (table 1). Nest height ranged from 3 m to 7 m with an average of 4. 7 m. Three unued nests were destroyed in bad weather and another was lost due to robbing of material by cormorants. Two nests that contained eggs were abandoned before hatching. During both years, nest construction was finished by early May. At all of the colonies there appeared to be a limit to the proximity of nests, since even when there was a 27 suitable site for another nest, none was built closer than about 1 m to another. The average distance between nests was 1.8 m. Dead twigs from various species of trees were the primary materials used in nest-building. However, large pieces of hardstem bullrush were often used. I was not able to identify the tree species used, but I often saw cormorants pick up dead twigs from the ground beneath the same trees they nested in. Large twigs were secured in the crotch of branches and then other twigs were interwoven until the nest was approximately .3 m high and .4 m wide (fig. 7). Nests which were used from the previous year tended to be higher and wider, due to the addition of material. The nest cup was lined with finer materials, including leaves and cormo- ra·nt feathers. occasionally, parts of live and dead bullrushes were also used to line the nest cup. Two nests, one new and the other rebuilt, were collected for comparison of building materials. The new nest had materials averaging 312 mm in length ( range 150 mm to 610 mm) and 7. 8 mm thick, the thickest being 26.0 mm. The rebuilt nest had materials averaging 333 mm in length (range 170 mm to 690 mm) and 8.1 mm thick, the thickest being 25.0 mm. Prior to measuring the nests were placed in Berlese funnels to collect invertebrates. A beetle, Dermestes lardarius, and several flies, Rhegoclema fil?•, were identified. 28

------

FIGURE 7. Geneva cormorant nest with an incomplete clutch of eggs. 29 Egg-laying

In 1973 egg-laying began at the Springville colony on 26 March and continued into late May. Egg-laying began at the Bay colony about 6 April and continued into early May, and at the Geneva colony, began on 13 April and continued until 17 May. At Geneva in 1972, 11 nests lost 1 egg or more before hatching. Three nests in tree 2 and one nest in tree 4 lost all the eggs before 10 May and in all four cases the same or a greater number of eggs were relaid by 29 May. In 1973, 12 nests lost 1 or more eggs prior to hatching. However, of the seven nests that eventually lost all eggs, no clutch was completely lost before 24 May, and no new clutches were laid.

Clutch Size

A census of the total number of eggs in each nest was kept by making weekly observations of the Springville a·nd Bay colonies and daily observations of the Geneva colony, then the maximum number of eggs present were counted before hatching began. A total of 126 eggs was found in the Spring- ville colony, for an average of 3.8 eggs per nest., and 28 eggs in the Bay colony for an average of 4.0 eggs per nest, in 1973. In 1972, a total of 80 eggs was found in the Geneva colony for an average of 4.2 eggs per nest and a total of 61 eggs., in 1973, for a 3.6 average. The average for all the colonies in 1972 and 1973 was 3.8 eggs per nest. Table 2 shows the number of eggs laid per nest in each colony. 30 TABLE 2. Numbers of eggs laid per nest at the Utah Lake Colonies.

Number of eggs/nest Colony Year 2 3 4 5 6

Geneva 1972 0 3 10 5 1

Springville 1973 2 6 21 4 0

Bay 1973 0 2 3 2 0 Geneva 1973 .! ...2 ll _Q Q TOTALS 3 16 45 11 1

Egg Measurements

Table 3 shows the ranges and averages of the sizes of eggs collected from the Utah Lake colonies over a three- year period. The average volume for all the eggs collected by Dr. Clayton White was 47.87 cc, with values ranging from 38.59 cc to 55.54 cc. The average volune for the Geneva eggs in 1972 was 48.43 cc, ranging from 44.14 cc to 53.23 cc. These volumes were calculated using the dimensions of 20 eggs which showed the clos~st increments to the average length and width. The average volume of 20 eggs from Geneva in 1973 was 49.66 cc with a range of 44.42 cc to 55.27 cc.

Hatching

Hatching at the Springville colony began on 22 April and continued until the second week in June. Of the J.26 eggs laid, 83 hatched for a success ratio of 66 percent (table 4). TABLE 3. Egg measurements from Utah Lake, showing range in length and width measurements with averages in parentheses.

Sample Date Colony Size Length (mm) Width (mm)

4/16/71 Bay 7 58.06 - 60.51 (59.70) 38.17 - 40.38 (39.00) a

4/27/71 Springville 7 58.34 - 64.05 (61.52) 35.47 - 41,33 (38,20) a

5/18/72 Geneva 48 56.80 - 63.90 (60.34} 36.90 - 41.00 (38.93) b a 5/2/73 Springville 10 58.08 - 64.52 (61.18) 37.17 - 40.08 (38.86)

5/8/73 Geneva 52 56.05 - 65.50 {60.52) 35.40 - 40.80 (39.05) b Total 124 Average (60.65) Average (38,80)

aWhite, personal communication. bThis study.

,...w 32 TABLE 4. summary of the nests selected for study at the Springville colony, in 1973.

Eggs Nest No. Height (m) No./Nest No. Hatched Percent

1 3.7 3 2 66 2 3.4 2 2 100 3 4.0 4 3 75 4 4.3 4 1 25 5 2.4 4 3 75 6 4.6 4 3 75 7 5.2 5 3 60 8 s.a 4 2 so 9 6.4 5 4 80 10 3.7 4 3 75 11 5.5 4 3 75 12 3.4 3 2 66 13 5.2 5 2 40 14 4.3 3 1 33 15 4.6 4 4 100 16 4.9 4 4 100 17 5.2 4 3 75 18 5.5 3 3 100 19 6.1 4 3 75 20 6.4 4 2 50 21 5.8 4 75 22 4.9 3 2 66 23 4.3 3 2 66 24 7.6 5 4 80 25 7.0 4 3 75 26 5.8 4 3 75 27 6.1 4 1 25 28 7.0 4 3 75 29 5.2 4 3 75 30 . 6.4 4 2 50 31 5.5 4 2 50 32 s.s 2 1 50 33 hl ---1 --1 75 Average s.2 Total 126 Total 83 Average 66 33 At the Bay colony, hatching began on 30 April and ended on 27 May, and 15 of the 28 eggs hatched, for a 54 percent hatching success (table 5). In 1972, hatching began at Geneva on 19 May and continued until 10 June with 44 hatchlings from 80 eggs for a 55 percent success (table 6). In 1973, hatching began on 20 May and lasted until 9 June. Only 18 of the 61 eggs hatched, for a 29.S percent hatching success (table 7).

TABLE 5. Summary of the nests studied at the Bay colony, in 1973.

Nest Height (m) Eggs No. No./Nest No. Hatched Percent

1 6.4 3 1 33 2 s.a 4 1 25 3 4.9 5 3 60 4 5.2 4 3 75 5 5.8 5 3 60 6 4.6 4 2 50 7 4.3 3 66 Average 5.3 Total 28 Total 15 Average 54

Measurements of the Young

Measureme·nts of the young in accessible nests were made at Geneva colony, in 1973. Due to the low hatching success, only 16 young were available for measurements and 3 of those died within 4 days. Figs. 8, 9 and 10 contain a summary of weight increase and length increase of beak and tarso-metatarsus. 34 TABLE 6. Summary of the nests selected for study at the Geneva colony in 1972.

Eggs Nest No. No./Nest No. Hatched Percent

1 4 3 75 .2 4 3 75 3 5 2 40 4 3 2 66 5 5 2 40 6 4 3 75 7 4 4 100 8 5 2 40 9 6 2 33 10 4 3 75 11 3 2 66 12 4 1 25 13 4 4 100 14 3 2 66 15 5 2 40 16 4 4 100 17 4 1 25 18 5 1 20 19 ....1 1 25 Total 80 Total 44 Average 55 TABLE 7. summary of the nests studied at the Geneva colony, in 1973.

Nest Eggs Young No. Height (m) No./Nest No. Hatched Percent No. Fledged Percent

1 7.0 3 0 0 0 0 2 4.3 4 0 0 0 0 3 6.4 3 2 66 2 100 4 s.2 4 0 0 0 0 5 4.3 2 0 0 0 0 6 4.3 4 2 50 2 100 7 4.9 3 2 66 2 100 8 4.9 3 0 0 0 0 9 4.0 3 2 66 2 100 10 4.6 4 0 0 0 0 11 3.0 4 4 100 1 25 12 4.6 4 0 0 0 0 13 4.9 4 0 0 0 0 14 4.9 4 0 0 0 0 15 4.6 4 1 25 1 100 16 3.7 4 2 50 2 100 17 hl 4 .2 75 3 100 Average 4.7 Total 61 Total 18 Average 29.5 Total 15 Average 83

w Ul 1600

1500 1400 1300

1200 1100 i 1000 900 E-4 -:x: (,!) 800 H rll1 ;J: 700 600 500 400 300

200 100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 DAY

FIGURE 8. Average daily increase in weight showing range of w daily measurements. 0' 80

i- 40 ::i:: z !j 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 DAY w FIGURE 9. Average daily increase in beak length showing range ....i of daily measurements. 70

50 -I 40 C) lo I..:I

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 DAY

FIGURE 10. Average daily increase in tarsometatarsal length w showing range of daily measurements. CD 39 Food Items

Food items were obtained from nestlings which regurgitated when I approached or handled them. Some items, which had been partially eaten, were taken directly from the nest. Remains of Black Bullhead (Ictaluruy melas), Carp (CyPrinus carpio), and Utah Chub (Gila atraria) were found at all three colonies; Goldfish were found only at Geneva.

Reaction to Human Handling

Daily handling of the young was necessary in order to take measurements. The behavioral response to these intrusions changed as the birds grew older, but some responses were common to all the young during certain age periods (table 8).

Banding

Bands from the o.s. Bureau of Sport Fisheries and Wildlife were attached to the right leg of nestlings, at Geneva., when they were at least 10 days old. In 1972, band numbers 628-64301 to 628-64308 inclusive were used. In 1973, band numbers 628-64309 to 628-64324 inclusive were used. This resulted in a total of 24 cormorants banded in two years.

Leaving the Nest

The dates stated mre pertain to the time when the birds were sufficiently developed to be absent from the nest 40

TABLE 8. Reactions to human handling by Double-crested Cormorant nestlings during specific age periods.

Age (days) Reaction

1-3 Can barely hold head upJ no physical resist- ance or escape attempts: cower and shiver when held; usually make no sound; crawl toward shade when exposed to sun. 4-7 Head held erect to peer at intruderJ make a whining sound; cower when hand reached out; attempt to hide behind nest-mates; sit quietly when head or eyes covered. 8-13 Defecate or regurgitate food when handled; peck at author's hand; squawk loudly, peck at nest-mate when placed back in the nest; quiet down after head covered. 14-22 Climb out of nest onto limbs away from intruder, defecate or regurgitate when approached; use toes and beak to hang onto any object within reach; will not remain quiet even when head covered; peck viciously when handled • 23- Climb frantically out of nest when approached; often fall or jump out of nest into water; swim well at first attempt. 41 and probably survive. This does not imply that the birds were able to fly when they left the nest. In all observed cases, the birds fell or jumped from the nest into the water and swam expertly away. This made it impossible to date when the fledglings were able to fly. The earliest date at which birds were absent from the nest, at Geneva, in 1973, was 17 June, and the last nestling left on 5 July. Age at the time of leaving was between three and five weeks. The oldest bird to leave was 37 days old and the youngest was 21 days old. The average age for leaving the nest was 29 days.

Departure Dates

After the young left the nest, the adults were seldom seen around the nesting area at the Bay colony and Geneva. At Springville, dozens of adults would return during the evening to roost for the night. Most cormorants leave the Utah Lake area in October, but in 1973 groups of 20 to 30 birds were observed on the lake, near Springville, as late as 18 November. I have never observed cormorants on Utah Lake after l December. DISCUSSION

A New Record

Breeding colonies of the Double-crested Cormorant have been reported in all the states in the continental United States. The subspecies, f• ~• auritus, is known to breed in most of the provinces of Canada and in most of the states east of Utah and north of Oklahoma. Utah breeding colonies have been found in Cache, Rich, Millard, Box Elder, and Davis counties. The only reference to breeding in Utah County was in relation to a collection of four cormorant eggs from Provo Bay, made by Robert Bee in 1920. This paper, then, is the first detailed report of the nesting of the cormorant on Utah Lake, Utah County.

A New Colony

on 20 June 1973, I visited the Newstate Gun Club located three miles west of Bountiful, Davis county, Utah. An unreported cormorant-breeding colony was located, nesting in Russian Olive trees (Elaeagnus angustifolia), along the south side of the Burton Canal. About 15 trees, averaging 8 m high, were scattered for 1 km along the canal. They contained 42 active nests with well-developed young. I saw a total of 66 young still in the nest and 23 immature birds were swimming in the canal. The birds in the canal had

42 43 apparently fallen or jumped out of their nests. While there, I saw four fledglings fall out of the trees while climbing on the branches. The trees, with cormorant nests, also contained a total of 61 Great Blue Heron nests with young. Numerous Magpies were seen foraging in the same trees. "Doc" Johnson, caretaker of the property, reported that the cormorants had nested there since 1962.

Utah's Cormorant Population

Behle (1958) reported a total of seven cormorant breeding colonies in Utah, but at that time, five had been deserted or destroyed. He made no mention of the colonies located on White Rock, Great Salt Lake, or Rock Island, Utah Lake. However, these two sites were limited to a few birds and probably used only a few times. Although the cormorants on Egg Island, Great Salt Lake, have not been studied since 1947, Behle (personal communication) thought that increased huma·n visitation to the state park on Antelope Island, which is .3 km from Egg Island, caused the cormorants to desert Egg Island in the early 1960•s. It is possible that the new colony at Newstate Gun Club, which began nesting in 1962, is a remnant of the Egg Island colony. The only other Utah cormorant colony still in use that I am aware of, other than the Utah Lake and Nevstate colonies, is at Bear River Migratory Bird Refuge. The colony consists of 2 groups of birds nesting on 2 small islands, one located in unit no. 4 and the other in unit 44 no. 5. The islands are devoid of vegetation and surrounded by water about .6 m deep. No other birds presently nest on the islands, although California Gulls were often seen flying nearby. This is the only colony still in use in Utah, where the birds utilize a ground-nesting environment (fig. 11). Although there is no published reference to nesting since 1949 (Behle 1958), records kept by the refuge personnel indicate continuous usage through 1973. The highest population was 106 nesting pairs in 1953; this dropped to 36 pairs in 1970. There were 47 pairs nesting there when I visited in 1973. on 9 May 1973, there were 15 nests containing 39 eggs on the unit no. 5 island. on 22 May 1973, there were

32 nests containing 23 eggs and 66 young on the island in unit no. 4. In 1973, the total known cormorant population of Utah consisted of 194 nesting pairs of birds located in five colonies. This does not compare favorably with the 500 to 600 birds nesting at Egg Island in 1915 (Palmer 1916), the 400 nesting cormorants at Bear Lake in 1929 (Behle 1935), or the 600 birds at Bear River Refuge in 1947 (Behle 1958). Behle (1935) reported a decrease in cormorant numbers on Egg Island from 500 in 1915, to 114 in 1935. He felt that the breeding cormorants in the region were threatened with extinction. Sugden (1936} noted an alarming decrease in the number of herons and cormorants nesting on the Great Salt Lake and made a plea for their protection. 45

FIGURE 11, Cormorants at Bear River Refuge utilizing a ground-nesting environment. 46 Arrival Dates

The cormorant arrives at its nesting grounds on Utah Lake in very early spring. Lockerbie (1942) stated that over a period of years, the earliest observation dates for cormorants in Utah was 29 March. The earliest cormorants have been seen at Bear River Refuge is 5 March (Behle 1958). The arrival of cormorant on 11 March 1972 at Springville during this study, is the earliest record for Utah. In 1972 and 1973, the first returning birds encountered very poor weather conditions and some ice remained on Utah Lake. It is interesting that the first birds returned to the Bay colony a week later than the Springville birds, and to Geneva about three weeks after the Springville birds. Yet, at the Bay and Geneva colonies, all of the birds that nested had returned within three weeks, but birds were still arriving at the Springville colony and building nests in late May. There must be some advantage for the first cormorants which return to Springville to offset the poor weather conditions to which they are subjected. It may be that since it is the largest colony, nesting space is at a premium and the first birds are assured of the choicest areas. Those birds that did not return to Springville until May, in 1973, were forced to build their nests west of the main cormorant colony. The reason for the time difference in return to each colony is puzzling. The Bay colony is subjected to essentially the same type of weather conditions as Springviile. Geneva may have somewhat different weather, but the pond is 47 always ice-free so the birds would have food any time. Bay and Geneva colonies are considerably smaller in numbers of birds than Springville colony, so th! lack of competition for nesting space may not require an early return.

It may also be that the birds in each colony remain associated at their wintering grounds and return as a group. Color-banding fledglings to determine if they returned to the same colony each year would help answer this problem.

Courtship and Nest-building

The detailed descriptions of courtship behavior (Lewis 1929; Mendall 1936; van Tets 1965) deal principally with ground-nesting cormorants. Although there are some differences, the behavior is essentially the same as that found in the tree-nesters. Lewis (1929) and Mendall (1936) described elaborate courtship taking place on land and in the water, but I observed neither. Lewis (1929) stated that the males returned to the nesting site from the previous year and staked out their territory. This was usually limited to an area two or three feet around the nest. I observed that the first returning males would claim old nests that were highest in the tree. They would then position themselves on the nest and attempt to attract passing females by "wing- waving" (van Tets 1965). To do this the male drops his breast forward and down, raises his head over his back with the mouth open and pointing skyward. The tail is raisP-d and held over the back, and, although not mentioned in the 48 literature, the bright-blue mouth and throat is exposed toward the female. With the primaries folded behind the secondaries, the wing tips are raised up and outward about once per second. This continues until a female responds and settles near the displaying bird. During this period the nuptial crests on male and female birds were easily seen, but were shed by mid-April. After the pair-bond is formed, the nest is defended from other birds. If a strange bird comes near the nest, a threatening posture is made by holding the neck in ans-shape and expanding the throat. Then, with the mouth open, lunging motions are made at the intruder. During nest-relief, recognition is usually accomplished when the bird on the nest exhibits a "gape display" (van Tets 1965). The neck is extended with the bill wide-open and the head is swayed from side to side. The birds would then rub necks or the male may bite the female•s neck. Sometimes, the returning bird would present a piece of nest material to the sitting bird. The relieved bird would then either immediately fly off to fish, or sometimes it would stand near the nest and preen its feathers. Lewis (1929) and van Tets (1965) cited exten- sive examples of call-notes given during courtship, but I heard none; possibly because of my distance from the nests. Before pair-bonding, nest material was brought to the nest only by the male. After the pair-bond was complete, both male and female would bring nest material, but no nest building took place until the female would stay and guard 49 the nest from other cormorants. Additional material was brought to the nest during the entire nesting season by both birds. After the nest was built, the male and female engaged in "nest-worrying" (van Tets 1965) while sitting on the nest. This principally resulted in the attempt to tuck loose twigs into the nest or break the twigs off.

Nests

The Double-crested Cormorant utilizes two different nesting situations, according to the environment. Most birds that nest along the Atlantic coast nest at ground level, on islands bare of vegetation (Bent 1922; Lewis 1929; Mendall 1936). Townsend (Bent 1922) found that the island nests consisted of a few sticks, but mostly seaweed, kelp, and grass. The nest dimensions averaged 52 cm across by 12 cm deep. Lewis (1929) described inland nests in Arkansas, Minnesota, and Quebec which were located in various species of trees, growing on islands or standing in water. The nests were located .3 m to 22 m from the surface of the ground or water. He reported that the nest dimensions averaged 48 cm x 22 cm and that there were never more than 6 nests in 1 tree. However, Palmer (1962) observed that trees have contained as many as 36 nests and I observed a tree with 11 nests at Springville. The nests consisted of dead twigs, devoid of bark, and the nest cup was often lined with green leaves or grass and gull or cormorant feathers. Mendall (1936) stated there was little affinity for a particular 50

species of tree used for nesting. The distance that the nest was located from the ground seemed unimportant. Four to six days was generally all the time needed to complete a new nest, but they were flimsy in construction. He stated that the cormorants did not seem to weave their nest materials. However, Behle (1958) found the nests on Egg Island, Great Salt Lake, consisted of twigs carefully woven together, and the nests I examined were very intricately interwoven. Palmer (1962) stated that rebuilding a nest took only two days, compared to four to six days to build a new one. Rebuilt nests were also much stronger than new nests. Rebuilding generally consisted of adding some material to the top of the old nest. He gave one record of a nest being reused for four years. I know of four nests at Geneva, which were used for at least three consecutive years. Unlike those described by Townsend and Lewis, Behle (1958) found that the ground-nesting cormorants at Egg Island built elaborate nests of sage and greasewood twigs. The twigs averaged 12 to 18 mm thick and 29 to 58 cm long. The nests were built on or near rocks and some of the nest cups were lined with gull feathers. Nests that had been used for more than one season were almost cemented solid with excrement. It is interesting to note that cormorants did not nest on the islands at Bear River Refuge until three years after the islands were built~ At that time rocks were placed at each end of the islands and cormorants then used them for nesting. Yet, Munro (1927), Behle (1958), and others report nesting 51 on bare ground in comparable island situations. From my observations in 1972, I concluded that old nests, in good condition, were the preferred nesting habitat. There was an order of preference from those highest in a particular tree to the lowest. Only after these were occupied were new nests built. Despite this general rule, in 1973 at Geneva new nests were built while old nests were left unoccupied. There is evidence (Palmer 1962; Lack 1968) that the most mature birds arrive at the colony and begin nesting first. If that was true, I felt that the higher nests in a colony should have a better hatching success, since the older birds would be more prolific and make fewer nesting errors (Lewis 1929). To check this hypothesis, I took the average of nest heights for each colony and determined the hatching success for the nests situated above the average as compared to those below the average (fig. 12). In every instance, contrary to my idea, the lower nests had a higher hatching success. This may indicate that the first returning birds are not necessarily the most mature birds, or possibly that the higher nests, which are more exposed (not shielded by leaves or branches) to the elements when the adults are disturbed, have a higher incidence of pre-hatching mortality. In addition, I observed cormorants bringing twigs to their nests that they had pilfered from an unoccupied old nest in tree 4 at Geneva. Birds, building nests in the same tree, continually took material from the nest until it was so depleted it fell out of the tree. On two other occasions, 52 a.o

7.5

7.0

6.5 67%

6.0 39% 19% s.s

-e s.o -E-t 62% ::i:: C> H 4.5 ::i::

4.0 69% 36%

3.S.

2.s

2 ..0 Springville Geneva Bay

FIGURE 12. Distribution of nest height, showing hatcring success above and below the average nest height. 53 I saw a cormorant land on the dike below the tree it was nesting in and walk up to a California Gull nest. It then took a twig from the gull's nest back to its own nest with- out any protest from the gull. In Utah, it seems to be the rule that cormorants nest in the same trees with Great Blue Herons. Presently in Utah, only the cormorant colony at Bear River does not nest in company with herons. Former nesting colonies in Utah, where herons nested with cormorants, were located at Bass Pond (Pearson 1927), cache Valley (Stanford 1937), and Egg Island (Behle 1958). However, this seems to be the exception throughout most of the cormorants' range since there are few other references to them nesting with Great Blue Herons. Howell (1911) and Stoddard (1922) reported them nesting with herons in Illinois and Wisconsin, respectively. Ganier (1933) described cormorants sharing a colony with Great Blue Herons, Water Turkeys, and American Egrets in Tennessee. They have also been reported nesting with Great Blue Herons and Black-crowned Night Herons in Nebraska (Lewis 1931). I have observed that when cormorants are nesting in the same trees with herons, the cormorant nests are always located below the level of the heron nests. Stanford (1937) noted the same thing at the colony in cache valley. At Spring- ville and Geneva, where only one heron was nesting in a tree occupied by cormorants, the heron's nest was the top-most in that tree. In 1972, at Geneva, the highest nest in trP.e 1 was utilized by a Great Blue Heron for nesting. In 1973, 54 the same nest was used by a cormorant, later deserted, and again used by a heron during the same season. If a heron nest was located at the same level as a cormorant nest, it was never situated closer than 3 m to it. This condition may exist for one of two reasons. Cormorants are noted for the large amount of excrement they deposit outside the nest, to the point that the very trees they nest in are often killed (Lewis 1929). The feces could also be harmful if it was deposited on heron eggs or young located underneath a cormorant nest. The most probable reason is the difference in take-off and landing patterns of the two birds. The cormorant is not an agile bird and, in order to become air- borne, must launch itself precipitously out of the nest (Hall 1926). I have observed that this may result in eggs or young being kicked out of the nest. Likewise, when they land at the nest, they will sometimes miss tp.eir footing and fall out of the tree or crash into their nest-mate or other cormorants nesting nearby. In comparison, the Great Blue Heron is able to fly away from the nest with considerable grace by launching itself straight into the air, or land at the nest with amazing agility so as to not disturb any of the nesting birds located nearby. Therefore, I feel that the stratification of the nests of these two species is a behavioral adaptation for partitioning the nesting habitat to avoid interspecific collisions, which could result in losses to eggs and young. The invertebrates that were discovered in the new and rebuilt nests should not be considered a definitive list 55 of what insects are found in company with cormorants. They are only examples of what may be found, and I have encountered no other list of this type in the literature. Further research may answer important questions, such as whether cormorants return to the same colony each year or even the same tree and nest. It is not known whether tree-nesting cormorants could effectively become ground- nesters. An attempt to get the ground-nesting cormorants at Bear River Refuge to nest in trees was successful when old nests were placed in nest boxes in an artificial tree made of 2 x 4's on the island in unit no. 4 (Gunther, personal

communication). It also needs to be determined whether cormorants could be enticed to a new nesting area by taking old nests from a former colony and placing them in a new location.

Egg-Laying and Incubation

The difference in the beginning egg-laying dates at each colony is a reflection of the time differential, in early arrivals, at each colony. There is a three-week period between the date of first arrivals and the date that eggs are first laid, so that eggs are laid first at Springville and last at Geneva. The eggs laid on 26 March 1973 at Springville, is the earliest record for Utah (Behle 1958), although Lewis (1929) stated that Utah had the earliest dates for any state and theorized that laying began during the second half of March. Five records from Utah, given by Townsend (Bent 56 1922), give dates of 9 April to 17 May for egg-laying. The earliest reported date for eggs laid in Utah was 28 March 1937 at Egg Island, Great Salt Lake (Behle 1958). In comparison, Palmer (1962) gives egg-laying dates for Arkansas from 7 April to 1 May and for South Dakota from l May to 6 June. Marshall (1937) reported a very late egg-laying date at Bear River Refuge, wherein nests contained viable eggs on 2 September 1936. Palmer (1962) stated that older colonies lay eggs before newer colonies, but that is not the case here, since Geneva colony has been in use since 1946 (Bee 1946) and Springville was not established until the early 1960•s. Eggs were laid over a 12-week period at Springville and for better than 4 weeks at Geneva (fig. 13), although the bulk of laying at Geneva came within a two-week period. After egg-laying was commenced, the female laid one egg per day until the clutch was complete, which was the same situation encountered by others (Lewis 1929; Mendall 1936; Behle 1958). However, Lack (1968) stated that cormorants lay eggs every two to three days. At Geneva, 90 percent of the females laid one egg per day until the clutch was complete. The other females took more than a day to lay one or more of their eggs. Lewis (1929) and Palmer (1962) reported that incubation usually began after deposition of the third egg. Men- dall (1936) and Behle (1958) observed that there is no rule and incubation may begin after deposition of the first egg or at anytime thereafter, until the last egg is laid. I found, in all observed cases, that incubation began 11

{I) 8

0 6

Ci 5 I 4 3

O 14 16 18 20 22 24 26 28 30 2 4 6 8 10 12 14 16 18 20 22 April May DATE

FIGURE 13. Distribution of egg laying at Geneva colony from 14 April to 20 May 1973.

U'I...., 58 immediately after the first egg was laid. This may be due to the fact that egg-laying begins early in Utah, while the weather is still very cool. The incubation period is given by Lewis (1929), Mendal1 (1936), and Behle (1958), as 25 days. Bergtold (1917) reported that most North American cormorants averaged 28 days for incubation and Worth (1940) gave the incubation period for the European Cormorant (Phalacrocorax carbo), which is not much larger in size than f• ~• auritus, as 28.5 days. van Tets (1959), working with the subspecies,~-~• cincinatus, in British Columbia, had 27 records for incubation, varying from 25 to 29 days, with most eggs hatching after 28 days. For the 16 Geneva hatchlings in 1973, I had records varying from 26 to 30 days with an average of 28 days for incubation. The difference, between the dates reported by others and my results, may again be due to early nesting and consequent cooler weather. In 1972, all the eggs from four nests at Geneva were lost before 10 May and a replacement clutch was laid for each by 29 May. The replacement clutch consisted of the same number of eggs as lost in three of the nests and one more egg than lost in the other. In 1973, although seven nests eventually lost all their eggs, no clutches were completely lost before 24 May and no replacement clutches were laid. Although not noted elsewhere, 30 to 50 percent of cormorants in Manitoba whose eggs or nests were destroyed before hatching, renested (Mccleod and Bondar 1953). It appears that as long as one of the original eggs remains in the clutch, there 59 is no urge to replace lost eggs. Also, there is apparently a point-in-time during incubation at which the female can receive a stimulus that will enable her to lay a new set of eggs. After that time, (10 May to 24 May?) she is unable to replace a lost clutch.

Clutch Size

The normal clutch size of the Double-crested Cormorant is three to four eggs, with four eggs most common (Davie 1900; Bent 1922; Lewis 1929; Mendall 1936). Palmer (1962) reported a range of two to seven eggs with one record of nine eggs. Levis (1929) found the great majority of birds nesting along the Gulf of st. Lawrence had a clutch of 4 eggs, "rarely" 5 eggs and 5 to 10 percent contained 3 eggs. Mendall (1936) reported the following percentages for Maines 2 eggs, 8 percent; 3 eggs, 40 percent; 4 eggs, 50 percent; 5 eggs, 2 percent. In a census taken on Egg Island, Great Salt Lake, in 1941, Behle (1958) found that over half the nests contained four eggs. The combined total of all the clutches from the Utah Lake colonies during the study wasa 2 eggs, 4 percent; 3 eggs, 21 percent, 4 eggs, 59 percent; 5 eggs, 14 percent, 6 eggs, 1 percent. These figures agree with other findings, although there is a greater number of clutches containing four and five eggs.

Egg Measurements

Measurements made of the longitudinal and transverse axes of the cormorant eggs indicate the Bay colony eggs have 60 the smallest average length and greatest average width of 59.7 x 39.0 (longitudinal x transverse in mm), while the Springville eggs show the greatest average length and smallest average width of 61.35 x 38.S. The Geneva averages are in-between at 60.43 x 38.99. Small variations from these measurements can be found in the literature, but they are remarkably slight when the large geographic distances sepa- rating the samples are considered. Townsend (Bent 1922) reported extremes of 65.42 x 42.0 and 56.0 x 36.5, with an average of 61.6 x 38.8 for 40 eggs in the u.s. National Museum. Lewis (1929) reported an average of 59.9 x 37.7 for 50 eggs, with extremes of 66.5 x 42.0 and 54.5 x 34.5. Mendall (1936) gives an average of 60.5 x 37.6 for 15 eggs measured. Behle (1958) measured 20 eggs from Egg Island, giving 64.0 x 39.4 and 53.0 x 34.8 as extremes and 59.3 x 37.1 as the average. The only significant deviations from these averages are the reports of Maynard ( 1890) a1nd Davie (1900). Davie reports the extremes as being 54.5 x 36.0 and 50.2 x 32.4 while Maynard's reported extremes are 60.0 x 36.0 and 54.0 x 32.4. Although the original measurements are given in inches, there should be very little accuracy lost in conversion to millimeters. These measurements are so much smaller than all other reported that their accuracy seems questionable. However, considering that they are accurate, it appears that both of these studies reported measurements of eggs from cormorants that, for physiological or genetic reasons, produced much smaller eggs than the generally observed average. 61 In a discussion on various means of measuring eggs, Preston (1968) stated that measuring all the eggs in a colony produced a bias toward the larger clutches. If measurements are being made in order to establish an average or norm for a species, it is the number of clutches or sets of eggs, not the number of eggs, that is important. He thought that a random selection of 1 egg from each of 20 or more clutches would be a better indicator for the species. In order to check that hypothesis, I took an average of all the eggs measured at Geneva in 1972, and in 1973. I then compared those averages with 3 random samples of 1 egg measured from each of 12 clutches during each year. T-tests at 5 percent (two-tailed) indicated that the random means were not signif- icantly different from the overall mean. However, since Preston recommends the comparison be done with 20 or more clutches, significant differences may appear in larger samples.

TABLE 9. Average length and width measurements of all eggs measured in 1972 and 1973, compared to random samples of one egg from each of twelve clutches.

Year sample Length (mm) Width (mm)

1972 Overall average 60.34 38.93 1972 1st random sample 59.67 39.18 1972 2nd random sample 60.38 38.74 1972 3rd random sample 60.69 38.94 1973 Overall average 60.52 39.05 1973 1st random sample 60.08 39.06 1973 2nd random sample 60.55 3°.26 1973 3rd random sample 60.67 38.92 62 Egg Volumes

Volumes for the eggs measured at Geneva, in 1972 and 1973, were computed in order to establish an average for f• ~• auritus, since no information on egg volumes is reported in the literature. The average volumes, given in tables 10 and 11, were calculated by using the formula, 2 Volume= 0.526 LB , where L = longitudinal axis, and B = transverse axis (Romanoff and Romanoff, 1949). Because of large variations in the egg measurements, it was necessary to use eggs that were closest to the average in length and width in order to arrive at an acceptable value. Ten eggs that showed the closest increments to the value for the average width and 10 eggs that were closest to the average length were selected. In tables 10 and 11, 3 eggs were duplicated in both categories, because they were close to the average in length and width. Volumes were calculated for each egg, along with the averages for the length and width categories. The volume averages for the two categories were only .42 cc apart and .86 cc apart, in 1972 and 1973, respectively. Because of the small variations, the average of 49.00 cc, for both years, appears acceptable. Romanoff and Romanoff (1949) have stated that the volume (V) for an egg can also be calculated, if the weight (y) is known, by the equation V = 0.933 Y• They have further refined this to v = 0.913 y for precocial birds and v = 0.959 y for altricial birds, such as the cormorant. ·.,:his seems a very unreliable method since cormorant eggs have a 63

TABLE 10. Volumes of eggs collected in 1972, from Geneva, showing variation of averages nearest width compared to averages nearest length.

Variation around average width (mm) Length (mm) Volume (cc)

38.60 60.10 47.10 38.70 58.55 46.16 38.70 60.05 47.35 38.70 60.70 47.82 38.75 58.90 46.64 38.80 63.75 50.52 38.90 60.00 47.76 38.90 60.85 48.47 38.90 61.70 49.11 39.05 63.75 51.31 Average 48.22

Variation around average length (mm) Width (mm) Volume (cc)

60.00 37.35 44.14 60.00 38.90 47.76 60.00 39. 70 49.74 60.05 38.70 47.35 60.05 39.30 48.83 60.05 39.55 49.57 60.05 39.55 49.57 60.10 38.60 47.10 60.10 39.35 49.07 60.20 41.00 53.23 Average 48.64 64

TABLE 11. Volumes of eggs collected in 1973, from Geneva, showing variation of averages nearest width compared to averages nearest length.

Variation around average width (mm) Length (mm) Volume (cc)

38.75 61.05 47.86 38.80 56.05 44.42 38.80 65.50 51.87 38.90 59.40 47.28 39.05 58.65 47.20 39.25 58.25 47.36 39.25 62.35 50.69 39.30 60.25 48.99 39.30 61.95 50.37 39.30 63.90 55.27

Average 49.13

Variation around average length (mm) Width (mm) volume (cc)

59.75 39.65 49.58 59.85 39.95 49.41 60.05 39.30 48.83 60.25 39.30 48.99 60.75 39.85 50.91 60.75 40.20 51.68 60.80 39.90 50.91 61.05 38.75 48.38 61.05 39.85 51.16 61.40 39.40 50.14

Average 49.99 65 tendency to lose weight after they have been incubated for some time. The average weight for 12 unincubated eggs was reported to be 46.9 gm, while 21 incubated eggs averaged 46.2 gm (Lewis 1929). As a further check on the reliability of this method, I calculated the volumes of 20 eggs, for which the weight was known, and listed the volumes computed for each egg by using both methods (table 12). The average weight of all the eggs was very close to the average of 46.5 gm for 50 eggs weighed by Lewis (1929). However, there is a difference of almost 5 cc between the average volume calculated from length and width measurement and the average volume calculated by weight. AT-test at 5 percent (two-tailed) indicated that this was a significant variation between these means. Further evidence of the unreliability of using weight to calculate volume is evidenced by comparing samples #18 and #20 (table 12). Although sample #20 is smaller in both dimensions, it weighs over 1 gm more than sample #18. There- fore, the formula given by Romanoff and Romanoff (1949) for calculating volume from the weight of the egg (V = 0.959 y for altricial birds) may hold true for some species, but is not accurate for the Double-crested Cormorant.

Hatching

The hatching dates reported for each colony reflect an average of 28 days for incubation. The earliest hatching began at Springville on 22 April 1973, but owing to the extended arrivals of new birds, lasted well into June. There 66 TABLE 12. A random selection of 20 eggs, taken at different times and from different locations, showing too volume as figured by length and width measurement compared to volume computed from weight. {Arranged according to increasing weight.)

Volumea Volumeb No. Width Length Weight (mm) {mm) (gm) (cc) (cc)

1 35.47 58.54 37.61 38.59 36.07 2 38.33 60.10 42.03 46.44 40.30 3 38.72 58.08 42.45 45.80 40.71 4 38.17 58.06 42.58 44.60 40.84 5 37.62 58.34 42,62 43.35 40.87 6 38.99 58.87 43.39 47.12 41.61 7 37.17 62.74 43.54 45.64 41.75 8 39.11 59.63 44.78 47.93 42.95 9 37.43 59.43 44.84 43.70 43.00 10 38.85 59.37 44.93 47.28 43.09 11 38.01 64.05 45.40 48.69 43.54 12 38.53 61.96 45.79 48.34 43.91 13 39.21 60.08 47.50 48.50 45.55 14 39.86 59.88 48.16 50.16 46.18 15 39.73 64.52 49.58 53.47 47.54 16 38.92 62.97 49.64 50.15 47.60 17 41.33 61.92 50.86 55.54 48.77 18 39.86 61.59 51.74 51.58 49.61 19 40.08 60.48 52.05 51.17 49.92 20 39.16 61.14 52.79 ~-39 50.63 Averages 38.73 60.59 46.11 47.87 44,22

a~olume as computed formula; volume= 0.526 length X breadth •

1\ro1wne as computed by formula; Volume= 0.959 x weight. 67 was a remarkable synchronization of hatching periods at Geneva during 1972 and 1973. In 1972, hatching began on 19 May and continued for 21 days, while in 1973 hatching began 1 day later and lasted 20 days (fig. 14). TWo to four days are usually required for the complete hatching of a single clutch, since incubation starts soon after the first egg is laid (Mendall 1936), although the hatching of the first and last bird may be separated by as much as a week or more (Palmer 1962). If this is the case, the youngest birds do not usually survive. It requires several hours for the complete hatching of each egg. Ricklefs (1969) stated that the hatching success for most colonial nesting birds should be above 50 percent. There is no report of hatching success for f• ~• auritus, but a record for P.a. cincinatus revealed a hatching success of 60.4 percent (Drent et al. 1964). The hatching success at Springville (66 percent) and Bay colony in 1973 (54 percent), and Geneva in 1972 (55 percent), give an average of 58 percent. That is probably a fair indicator for the species, although the hatching success for ground-nesting cormorants may vary considerably from that value, due to other external factors. The very low hatching success at Geneva in 1973 (29 percent), requires some explanation other than predation. I believe that the daily visits I made to Geneva, in combination with the cool weather during incubation, may principally account for the low success. In order to complete my daily counts, it was sometimes necessary to keep the adults from the nest for as long as 45 minutes, 7

Q 5

4 3 Cll g 2 rs1 1 Q.______...______.______..,______19 20 21 22 23 24 25 26 27 . 28 29 30 31 l 2 3 4 5 6 7 8 9 10 11 May June DATE

FIGURE 14. Distribution of egg hatching at Geneva colony from 19 .May to June 1973.

O'I Q) 69 although the interval was usually less. While awaiting my departure, the adults flew to the reservoir and when I left immediately flew back to the nest. Their moist feathers and water on the eggs may have resulted in an extended period before optimum incubation temperature was again reached (Lack 1968). Ricklefs (1969) stated that high temperatures of eggs, caused by exposure to the sun, is a serious mortality factor. This may have contributed to the mortality of some eggs in exposed nests, but is probably not an important factor, since temperatures were not high until the last of May, when 90 percent of hatching was already complete. Seven of the Geneva nests, which were regularly attended by the adults in 1973, had no hatchings at all. These nests were completely composed of addled eggs for a total of 39 percent of all Geneva eggs. That is considerably higher than the 24 percent of addled eggs reported for a colony of ground-nesting cormorants (f. ~• cincinatus) in British Columbia (Drent et al. 1964). All the nests at Geneva, which contained only addled eggs, were still being incubated by the adults two weeks after the e:xpected hatching date. Three of these nests were still being incubated 30 days after the estimated hatching date. Incubation of addled or infertile eggs beyond the normal incubation period is well docwnented (Snow 1960).

Predation of Eggs and Young

Predation on the eggs and young of cormorants is a commonly noted occurrence. Ferry (1909) observed predation 70 by Ring-billed Gulls (Larus delawarensis) on the eggs of cormorants in Saskatchewan. Lewis (1929) reported predation on eggs and young by Great Black-backed Gulls (Larus marinus), Crows (Corvus brachyrhynchos), and Ravens (Corvus corax). This only occurred when the adults were absent from the nest, since they are usually intrepid defenders of their nests. Herring gulls (Larus argentatus) have also been observed attacking eggs and young of unguarded cormorant nests (Mendall, 1936; Bourget 1973). At Mandarte Island, in British Columbia, crows and gulls removed eggs from nests that had been vacated for only a few minutes (van Tets 1959; Drent and Guiget 1961), and 28 percent of the eggs in the colony were lost due to these predations in 1963 (Drent et al. 1964). California Gulls are known to attack and consume the eggs and young of unguarded nests (Odin 1957; Behle 1958). The personnel at Bear River Refuge informed me that they had to employ methods to discourage gulls from nesting, because they were so destructive to the eggs and young of water birds, including the cormorant. There are no records of mammalian predators on the eggs and young of cormorants and Lewis (1929) reported that even when there were large numbers of coyotes (Canis latrans) in an area where a nesting colony was accessible, they were never known to attempt any attack. Contrary to these reports and the statement made by Armstrong (1965), that gulls always attack eggs in vacated cormorant nests, I have never observed mammalian or avian predation at any of the Utah Lake colonies during this study. In addition, I have never seen any evidence of predation, 71

such as broken eggs, ravaged young, etc., which would indicate attacks during my absence. After reviewing these reports, I expected serious problems, from the California Gulls, when I disturbed the nesting birds at Geneva. But even when I kept the cormorants from their nests for as long as 45 minutes, I never observed an aggressive act toward the eggs or young from a single gull, though hundreds were flying nearby.

Measurements of the Young

Three measurements of the nestlings were taken in order to determine growth patterns. Each bird was weighed and linear measurements of the beak and tarsometatarsus were made daily. Since hatching was sporadic and took place at all hours of the day, it was impossible to tell how long a bird had been hatched. For this reason, it was only possible to obtain a meaningful average for measurements from the four hatchings I witnessed. Therefore, the graphs shoving growth (figs. 8, 9 and 10), begin on the first day after hatching. The average weight at hatching was 36 gm and tarsometatarsal length was 11 mm. This is close to Lewis' (1929) measurements of 37 gm and 12 mm for weight and tarsometatarsal length respectively. Mendall (1936) reported an average weight at hatching of 32 gm. The average beak length of the Geneva birds at hatching was 17 mm, but Lewis (1929) reported an average length of 11 mm. The discrepancy is due to different .measuring techniques. I measured along the side of the beak from the corner of the mouth to the tip of the upper 72 mandible, and Lewis measured from base to the tip, along the top of the beak. The average weight for Mendall's (1936) birds at 5 days was 158 gm, and mine averaged 156 gm. At 14 days, Lewis (1929) reported an average weight of 778 gm, Mendall reported 785 gm, and mine averaged 736 gm. When 20 days old, the Geneva young averaged 1158 gm and Mendall (1936) recorded an average of 1232 gm. The average weight for the Geneva young after the 23 day period was 1543 gm. Consider- able weight addition takes place thereafter, since Lewis (1929) gave the average weight for adult males as 2100 gm and adult females as 1670 gm. That may be a low average because the average weight given for 10 adult males in Maine was 2233 gm and for 12 adult females was 1861 gm (Kury 1968). Other than the averages recorded at hatching, there is no additional information for measurements of beak and tarsometatarsal growth in the literature. When 23 days old, the young had an average beak length of 73 mm and an average tarsometatarsal length of 58 mm. Palmer (1962) records the average tarsometatarsal length of adult birds as 61 mm. Measurements of an immature cormorant in the BYU Life Sciences Museum indicated a beak length of 89 mm and tarsometatarsal length of 58 mm. The relationship of these measurements to the growth patterns values are indicated in figs. 8 and 9.

The growth curve of the beak indicates continual increase through the 23rd day, but the tarsometatarsal length levels out at approximately 57 mm after the 19th day. 73 Development of the Young

Detailed accounts of the physical and behavioral development of young cormorants can be found in the literature (Lewis 1929; Mendall 1936). However, a general descrip- tion of some major events during development is necessary here for continuity. When too young birds hatched, they were naked, blind, barely able to move, and had a taut black skin, although Lewis (1929) and Mendall (1936) reported that they had a dark-brown skin that turned black within a day or two. During the first few days after hatching, the oldest birds in the clutch were very aggressive. That sometimes resulted in the smaller or younger birds being deprived of food from the adults and becoming so weakened they died of starvation (Hall 1926; Behle 1958). At Geneva three young died when only a few days old, apparently of starvation, while their siblings grew normally and continued in good health. Although this may be the major cause of death of fledglings, very young birds are also susceptible to death during hot weather. on hot, sunny days it was necessary for the adults to shade the young. If the adults were frightened from the nest, I have seen the young die within minutes. Of the 18 young that hatched, 15 survived long enough to leave the nest, for a fledgling success Of 83 percent (table 7). After they are a week old, the birds were better able to move into shade and employed gular flutter to cool themselves (Bartholomew et al. 1968; Lasiewski and Snyder 1969), altoough Mendall (1936) dismissed gular flutter as merely rudimentary 74

instinct. The eyes opened after the birds were about 5 days old and the egg tooth dropped off at 4 to 7 days, although some birds retained the egg tooth for as long as 12 days. A fine black down appeared about the sixth day and eight days later the bird was completely covered. After the young were two weeks old they were very adroit in the use of beak and feet for grasping. When taken out of the nest, they would grab onto anything with their beak and toes and it was difficult to dislodge them. I observed a four-week-old bird climb 5 m up a tree, to the nest from which it had fallen. From hatching until about two weeks old, the young were fed a semi-liquid diet by regurgitation from the adults. After this, whole or partially-eaten fish were brought to the nest and eaten by the young birds. At 17 to 19 days the flight feathers first 8ppeared along the alar tracts and the light- colored gular pouch became a deeper yellow (fig. 15). The birds were fully feathered at eight weeks and were easily recognizable on the water or in flight by their brownish back and cream-colored breasts, in contrast to the glossy black of the adults.

Food Items

Most of the studies dealing with the food of the Double-crested Cormorant have been done with birds nesting along the Atlantic coast (Lewis 1929; Mendall 1936). There- fore, they contain lists of marine species of fish and do not provide good information on the food habits of inland cormorants. Records of the Biological survey (Lewis 1929) 75

FIGURE 15. Geneva fledglings that are approximately 24 days old. 76 showed 9 birds collected at the mouth of Bear River contained the following stomach contents: Carp, 73 percent; Utah sucker (Catostomus ardens), 19 percent; Chub (Leiciscus lineatus),

3 percent; Chub (Leuciscus _fil2.), 6 percent. Behle (1958) found the following species regurgitated by young birds at Egg Island, Great Salt Lake: carp; catfish; Yellow Perch (Perea flavescens); Silverside Minnows (Richardsonius hydro- phlox)J ~nd Webug suckers (Catostomus fecundus). Other records (Lewis 1929; Mendall 1936) have reported cormorants taking Bluegill Sunfish (Lepomis pallidus), Pumpkin-seed Sunfish (Lepomis gibbosus), Northern Crappies (Pomoxis sparoides), common Crappies (Pomoxis annularis), Pike(~ lucius), Walleye (Stizostedion vitreum) and a mudpuppy (Necturus maculosus). Palmer (1962) recorded crayfish, frogs, Fathead minnows (Pimephales promelas), and dace (Rhinicthis ~-) as additional food items. Uhler (Lewis 1929) found that cormorants nesting on Stump Island, North Dakota, had an unusual diet. The stomachs of 17 birds contained the following speciesa Tiger Salamanders (Ambystoma tigrinum), 75 percent; Bullhead (Ictalurus nebulus), 20 percent; Stickle- back (Euclania inconstans), 5 percent. He attributed the large numbers of salamanders taken to the fact that the lake was drying up and the waters had become so alkaline, that only the Stickleback could survive. The birds were then forced to take most of their food from nearby prairie sloughs. Of the four species of fish, the Geneva fledgli.ngs were observed to use for food, the Utah chub and goldfish are noted for the first time. The fish found regurgitated ranged 77 in size from 3 cm (goldfish) to 22 cm (bullhead). The cormorants on Utah Lake do not fish in large cooperative groups ~s reported by Bartholomew (1942) on San Francisco Bay, but are generally solitary in their fishing activities (Behle 1958). Even so, I have seen groups of four to six birds pursuing schools of goldfish in the Geneva reservoir. The Geneva birds were often observed fishing in the reservoir in 1972. When the nest-mate was relieved from incubation, it would usually fly to the surface of the reservoir and commence fishing. However, in March 1973, iron sulfate was placed in the reservoir to inhibit the growth of algae. This apparently killed many of the fish, since very few were seen during March, April, and May. I observed that during that period the birds• fishing behavior also changed. The off-duty bird no longer settled on the reservoir to fish, but instead flew in the direction of Utah Lake. The lack of nearby supplies of fish may explain the 50 percent reduction in nesting pairs from 1972 to 1973 (table 13). In June, there was an increase in fish numbers in the reservoir and the adults began fishing there again.

TABLE 13. Numbers of active nests in the Utah Lake colonies over a four-year period.

Year Springville Bay Geneva Totals

1970 Unknown 14 26 Unknown 1971 68 17 18 103 1972 48 12 31 91 1973 83 6 15 104 78 Banding

As of 1957, 21,157 Double-crested CorDK>rants (all four subspecies) had been banded as preflight young, with 2,579 returns. The main areas of banding for the subspecies, f· E• auritus, were Maine, Ontario, Quebec, Saskatchewan, and South Dakota. Cormorants have also been banded in Illinois, Manitoba, Massachusetts. Michigan, Minnesota, Montana, New Brunswick, New York, North Dakota, Wisconsin, and Wyoming. Lewis (1929) and Mendall (1936) cited exten- sive data for birds banded in Canada and along the north Atlantic Coast. The most intensive banding done near Utah was at South Waubey Lake, South Dakota (Lundquist 1932). These studies and others (Hickey 1951) indicate a general southeast movement from ttE nesting grounds to the wintering grounds in Alabama, Florida, Louisiana, and Mississippi. The cormorant is likely the most neglected waterbird in Utah as far as banding is concerned. The first cormorant banded in Utah was a single bird banded by Alexander Wetmore in 1915, at Bear River. Another 57 birds were banded at Bear River in 1936, 1938, and 1947 (Van den Akker and Wilson 1949). A total of 30 birds were banded at Egg Island, Great Salt Lake, in 1933, 1934, 1939, and 1947 (Behle 1958). I banded a total of 24 nestlings at Geneva in 1972 and 1973, which is almost one-third of the total banded over the previous 32-year period. Although Palmer (196-2) reported no recoveries from Utah, there have been five band recoveries reported in the literature from within Utah. Wetmore (1923) 79 recorded that a bird he had banded at Bear River on 3 July 1915 was recovered 3 months later, 12 miles northwest of Salt Lake City on the Jord~n River. A band was recovered from the skeleton of a young bird on 10 April 1935, on Egg

Island. The bird, banded as a nestling the year before, had never left the island (Behle 1958). Another record was of a bird banded 24 June 1938 at Bear River and found dead in October of the same year, near Salt Lake City. TWo other records reported by Van den Akker and Wilson (1949) from Bear River, indicated that the birds are rather long lived and return to the same area to nest. One bird banded 10 September 1936 was recovered 8 years later at Bear River on 6 July 1944. This is the longest life span for a wild cormorant recorded that I could find in the literature (Lewis 1929; Mendall 1936). Another bird banded on the same date was recovered 26 April 1937, at Bear River. An important, but heretofore unpublished return, was obtained directly from the Bird-Banding Office. A cormorant banded 10 June 1948 at Bear River was shot 4 months later on 10 October, near the Colorado River on the Nevada-Arizona border. The impor- tance of this return will be discussed in a following section.

Leaving the Nest

There is little agreement among authors as to when young cormorants first leave the nest, and how they accom- plish their departure. Some, but not all, of the variation can be explained by the difference in nest location, such as 80 nesting on low islands, on cliffs, or in trees. Townsend (Bent 1922) noted that the young remained in the nest until fully feathered and flew at about eight weeks of age. How- ever, if they fell into water before they could fly, they would make no attenpt to swim. Lewis (1929) reported that

the young stayed in the nest (in trees) until about six weeks old, when they made their first attempts to fly. Mendall (1936) observed that young birds flew feebly to the water from cliff nests at six weeks of age, but were not able to dive until seven weeks old. Lack (1968) stated that cormorants remained in the nest until they could fly and did not swim until after they were able to fly. Cormorants on Egg Island, Great Salt Lake, were observed to swim and dive long before they were able to fly, although no age was noted for either event (Behle 1958). In contrast, Burns (1921) found that the young usually fell, rather than flew, into the water from nests in trees. Some of these birds were only 17 days old when they fell from the nests. I have observed that very few tree nesting cormorants in Utah remain in the nest until they are able to fly. I observed that after the young were approximately three weeks old, they would leave the nest and move onto the limbs of the tree in order to increase the distance between them and me; which often resulted in young birds falling into the water. At first I suspected that they had drowned, but I later observed that they would swim away as far as 30 m underwater. After a large number had fallen out of the nest they could be seen swimming in groups some distance from the colony. 81 I thought that this was an unfortunate situation caused by my presence only, until I visited Nevstate Gun Club in June

1973. At the time of my visit, the birds had not been disturbed for 3 weeks, yet when I arrived at the colony, there were 23 immature birds swimming in the canal. I satisfied myself that they were not able to fly by chasing them up and down the canal, and observed that they were between 4 and 6 weeks old. While I was there, more young fell into the water and two birds that fell onto the ground immediately walked over to the canal and swam off. This early departure from the nest requires the young to quickly learn to fish or to continue to be fed by the adults (Levis

1929; Mendall 1936; Behle 1958). I have never observed young cormorants being fed on the water, but assume the adults continue to feed them until they are able to fish effectively for themselves.

Departure Dates

Most of the local cormorants leave the Utah Lake area in October. Although I have seen them on Utah Lake as late as 18 November, there is no way to tell if these are local birds or others migrating through. The latest date they have been seen at Bear River is 1 December (Behle 1958). Palmer (1962) stated that almost all of the Atlantic coast migrants have arrived at their wintering grounds in Texas and Louisi- ana by 1 December. An unusual sighting was made by Rer-d Ferris in 1959 (Scott 1959) when he saw a cormorant at Geneva reservoir, on 1 January. Since the reservoir is supplied 82 with warm water, it does not freeze during the winter and the bird would be able to fish. However, there vas no way to tell whether the bird was a late southern migrant, a bird that overwintered here, or a very early arrival. It is also possible that the bird experienced a physical problem during migration south and was forced to remain at the only area available for fishing.

Subspecific Status

The subspecific status of the cormorant in Utah has been an object of confusion for almost 70 years. Goodwin (1906) identified two skins of birds taken near Vernal as the Farallon Cormorant (f. dilophus albociliatus; now f• auritus albociliatus), although he did not justify the basis for his conclusion. The A.o.o. Check-list (third edition, 1910) recognized f• ~• auritus as the subspecies breeding in Utah, and Lewis (1929) and Peters (1931) reported the same thing. However, the fourth edition of the A.o.u. Check-list (1931) substituted P. ~• albociliatus for f• ~• auritus. In an attempt to solve this problem, Behle (1936) examined the nuptial crests of six specimens taken from Egg Island, Great Salt Lake. The Pacific coast subspecies, albociliatus, has predominantly white plumes in the crests, while black plumes predominate in the eastern subspecies, auritus. Although the birds from Egg Island displayed a mixture of black and white plumes, Behle designated th~m as auritus because of the predominance of black plumes in the crests. I have observed a large number of white plumes in 83 the principally black crests of the birds on Utah Lake. There is a great amount of variation in these two subspecies with a gradual change from black plumes in the eastern birds to white plumes in the Pacific coast birds (Baird et al. 1884). Mendall (1936) considered Behle's (1936) evidence inconclusive, due to the small sample size, and continued to recognize the Utah cormorant as albociliatus. Behle (1941}, in a later article, refuted the sug- gestion of Peters (1931) and Mendall (1936) that albociliatus may have nested in Utah at one time. This time, Behle ( 1941) based his conclusion that the Utah birds were auritus, on the examination of the crests of 26 birds collected from Egg Island. He pointed out that the birds at Salton sea, Imperial County and Buena Vista Lake, Kern County, California, exhib- ited a great deal of vari~tion in numbers of black and white plumes, but were designated albociliatus, because white plumes predominate (van Rossem 1936). In addition, he stated that the cormorants from Utah were intermediate in size between the eastern and western subspecies. Townsend (Bent 1922) was the first to suggest that the Utah birds could be intermediates between the two subspecies. on the basis of the average wing length (flattened) of 12 males, he concluded that the birds from Egg Island were larger than albociliatus and smaller than auritus. Behl.e (1941} stated, "From the west coast to the east coast, the trend is toward increase in size ••• •" Yet,his measurements of 5 mates (albociliatus), from the Salton Sea, averaged 5 mm larger th8n the Utah males. His basis for the eastern birds being 84 larger than the Utah birds was an average wing measurement of 345 mm for 2 males from Minnesota. That average is considerably higher than even the extremes reported in the literature. though there may be some variation due to different measuring techniques. Lewis (1929) reported wing measurements of 291 mm to 325 mm for cormorants from Maine. Dawson (1903) recorded the average wing length of birds from

Ohio as 330 mm and Sutton (1967) reported the average for cormorants collected in Oklahoma as 324.8 mm (flattened). Contradicting Behle (1941). Palmer (1962) has stated, "Average size increases ••• from east to west in the range of the species." He further stated that albociliatus was slightly larger than auritus, but gave the average wing measurement for males of both subspecies as 311 mm. Moreover. if we assume that a larger egg indicates a larger bird (Lack 1968); then Davie (1900). Reed (1904), Townsend (Bent 1922), and Palmer (1962) supplied evidence that albociliatus is the larger bird. Behle {1941) stated that it might shed some light on the situation to know the status of the cormorants at Pyr~mid Lake, Nevada. However. these birds have been designated for some time as albociliatus (Hall 1926; Bond 1940; Linsdale 1951), although no information is provided describing the plumes. Therefore, only additional measurements of a large number of specimens, from many localities, can provide a definitive answer to the problem of size. Evidence does exist, however, that indicates that the rJtah birds are intermediate between the two subspecies in size. as well as in crest color. 85 If we accept the postulate that the Utah cormorants are intermediates, then we must supply some evidence for the origin of this situation. The returns from P. ~• auritus banded in other western states (Colorado, North Dakota, and South Dakota) indicate that all of those birds migrate in a southeastern direction and winter in the Gulf states. Behle (personal communication) believes that the cormorants nesting in Utah winter in southern California or Baja, in the same area as the Farallon Cormorant. In this regard, the return from the cormorant banded at Bear River Refuge in 1948 and recovered near the Colorado River on the Nevada- Arizona border in October of the same year, becomes very significant. That bird's line of flight from Utah, if continued, could have taken it into southern California. Addi- tional evidence that the Utah birds migrate to southern California is provided by sightings made in southwestern Utah during the periods of spring and fall migration. They have been observed at Kanab, Kane County, on 21 April 1931 (Behle et al. 1958). Stanford (1931) observed cormorants at Red- mond Lake, Sevier County in March and April 1929. Williams (1939) sighted 17 birds on 16 October 1939 at Piute Reser- voir, Piute County, and he also saw 33 and 31 cormorants on 12 September and 13 October 1939, respectively, at Otter Creek Reservoir, Piute County. Two birds were observed and one was collected at Ivins Reservoir, Washington County, on 20 April 1940 (l!ardy and Higgens 1940). They have also been observed on the South Fork of the Virgin River, "during migration" (Wauer and Carter 1965). 86 However, these sightings are not conclusive proof that the Utah birds actually winter in the same area as P.a. albociliatus. Returns from southern California, of birds banded in Utah, will provide us with actual evidence that the 2 species could congregate together at their wintering grounds. If that is the case, then it is possible that some Farallon Cormorants could have returned to the nesting grounds in Utah and through interbreeding may have established a population intermediate in size and crest color.

Effects of Diking Provo Bay

In 1973 there were 388 cormorants nesting in 5 known colonies in Utah. Provo Bay was the nesting area for 178 of these birds, or 46 percent of the state's total known cormorant population. The proposal to dike and drain Provo Bay as part of the Central Utah Project (fig. 2) would eliminate the nesting area of these birds. Cormorants have been resi- dents of Provo Bay, since at least 1920, and as many as 300 birds have nested there at one time (Bee 1949). There has been 2t stable, cormorant population of about 100 nesting birds on Utah Lake for the past three years {table 13). It has been suggested by the advocates of the Central Utah Project that the displaced birds could locate elsewhere on Utah Lake. owing to the unusual nesting requirements of these cormorants (undisturbed trees in shallow water), this is unlikely. There are only two probable sites for reloca- tion directly on the lake. One is a small group of dead cottonwood trees on the southwest side of the lake which is 87 currently utilized by Great Blue Herons. cormorants have not nested there before, possibly because of lack of nesting space. Another location is about .3 km west of Powell Slough in some low-growing trees. Again, cormorants have never nested there, probably because the site is too accessible from the shore. Some of the displaced birds could relocate at the Geneva colony, but the rookery would only have nesting space for about 40 pairs, leaving 80 percent of the cormorants still homeless. It is possible the cormorants could establish a new colony, but since seven former colonies have been deserted there must be a paucity of acceptable sites. It would then remain for the evicted birds to relocate at one of the two remaining colonies in the state. Yet again, there is not sufficient nesting space for all of them to roove to the Newstate Gun Club area. The two island colonies at Bear River Refuge could provide room for all the displaced birds, but it is unknown whether tree nesting birds could adjust to a ground nesting habitat (Hilden 1965). Cormorants have been subjected to persecution, for various reasons, in the united States and Canada for years. Entire colonies have been wiped out and their numbers reduced by the thousands (Smith 1911; Demille 1926; Lewis 1929; Stanford 1937; Buchheister 1944; McLeod and Bondar 1953). The reduction of cormorant numbers in Utah has been no less serious {Behle 1935; Sugden 1936), and the diking of Provo Bay will only compound an already critical situation. SUMMARY

The Double-crested Cormorant (Phalacrocorax auritus auritus) nests at three locations on Utah Lake, Utah County, Utah. The earliest date the birds arrived at their breeding grounds W8s 4 March 1972. The types of behavioral displays observed included wing-waving, nest-worrying, threat, and recognition displays. Nests in good cmdition from the previous year are occupied first by returning birds, and new nests are built when these are taken. In 1973, there were 86 active nests at the Springville colony, 7 at the Bay colony, and 15 at the Geneva colony. A beetle, Dermestes lardarius, and several flies, Rhegmuclema :!E• were found in the nests. At Geneva, in 1973, egg-laying occurred from 13 April to 17 May. The average clutch size was 3.8, ranging from 2 to 6 eggs. The average egg length and width was 60.52 mmx 39.05 mmand the average volume was 49.0 cc. The average period of incubation was 28 days. Hatching took place from 20 May until 9 June. The hatching success was 55 percent in 1972 and 29.5 percent in 1973. In 23 days, the average weight of the young increased from 36 gm to 1543 gm; the average beak length from 17 mm to 73 mm; and the average tarsometatarsal length from 11 mm to 58 mm. The age of the young can be estimated by observing 88 89 appearance and behavior. The young usually fell out of the nest before they could fly, but were able to swim well. Observed food items of the fledglings consisted of carp, Utah chub, bullhead, and goldfish. The cormorants left the Utah Lake area to migrate south in October and November. The subspecific status of the cormorants nesting in Utah has been designated as f• ~• auritus. There is still some question as to whether they are intermediates between f• a. auritus and f• ~• albociliatus. The diking of Provo Bay would eliminate the nesting sites of 178 cormorants with little possibility for reloca- tion on Utah Lake. REFERENCESCITED

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Ronald M. Mitchell Departmnt of Zoology M.S. Degree, April 1974

ABSTRACT Research on the nesting of the Double-crested Corm rant (Phalacrocorax auritus auritus) was udertaken to deter mine th nesting ecolog of the bird on Utah Lake, Utah County, and the possible effects that diking Provo Bay would have on the cormorants breeding there. In 1973, two colonies in Provo Bay were visited weekly to determine laying dates, incubation period, clutch size, and htching dates. Another colony, located on the dike of the Geneva Steel Reservoir, was visited daily during the spring and summer of 1973. At this colony, egg-laying occurred from 13 April to 17 May. The average clutch size was 3.8, and the egg length and width averaged 60.50 m x 39.05 m. An average egg volume of 49.0 cc is first reported for the subspecies. The average period of incubation was 28 days, and 29.5 percent of the eggs hatched, bgining on 20 May and ending 9 Jue. The young weighed an average of 36 gm at hatching with a bak length of 17 m and tarsomtatarsal length of 11 mm. These increased to 1543 gm, 73 mm, and 58 m, respectively, in 23 days. The cormorant population on Utah Lake my b severely reduced by the diking of Provo Bay. COMITTEE APPROVA: