Breeding Biology of the Double-Crested Cormorant on Utah Lake Ronald M

Great Basin Naturalist

Volume 37 | Number 1 Article 1

3-31-1977 Breeding biology of the Double-crested Cormorant on Utah Lake Ronald M. Mitchell Southwest Research Institute, San Antonio, Texas

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Recommended Citation Mitchell, Ronald M. (1977) "Breeding biology of the Double-crested Cormorant on Utah Lake," Great Basin Naturalist: Vol. 37 : No. 1 , Article 1. Available at: https://scholarsarchive.byu.edu/gbn/vol37/iss1/1

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Volume 37 March 31, 1977 No. 1

BREEDING BIOLOGY OF THE DOUBLE-CRESTED CORMORANT ON UTAH LAKE'

Ronald M. Mitchell-

Abstract.— Research on the nesting of the Donble-crested Cormorant (Phalacrocorax auritus auritus) was un- dertaken to determine the breeding biology 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 hatching dates. Another colony, located on the dike of the Geneva Steel Works Reservoir near Oreni, 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 mm x 39.05 mm. The average period of incubation was 28 days, and 29.5 percent of the eggs hatched, beginning on 20 May and ending on 9 June. The young weighed an average of 36 gm at hatching with a beak length of 17 mm and tarsometatarsal length of 11 mm. These measurements increased to 1543 gm, 73 mm, and 58 mm, respectively, in 23 days. The cormorant population on Utah Lake may be severely reduced by the proposed diking of Provo Bay.

There have been no detailed studie.s of likely the least understood water bird nest- the biology of the Double-crested Cormo- ing in Utah. rant {Phalacrocorax auritus auritus) in Utah, Although there are three other subspecies other than a brief but noteworthy account (P. a. albociliatus, P. a. floridanus, P. a. cin- by Behle (1958) of those birds that nested cinatus) found in North America, P. a. au- on Egg Island, Great Salt Lake. Two de- ritus is considered the most important due to tailed studies of this subspecies have been its wide distribution, ranging from central conducted on the Atlantic coast (Lewis Canada to Texas and from the Atlantic 1929, Mendall 1936), but no extensive ac- coast to Utah. The P. a. auritus populations counts of breeding biology exist for Double- in Utah are the westernmost breeding colo- crested Cormorants found nesting inland. nies found in the United States and provide This lack of scientific data may be due in excellent contrast for compari.son with the part to a lack of qualified and interested ob- previously studied birds nesting along the

.servers, but I feel it is principally due to Atlantic coast. the sentiment expressed in the following The few publi.shed references that exist quotation:"God no doubt had his reasons for concerning Utah's cormorants are little creating each living thing, but when he cre- more than sight records or brief mentions of ated the cormorant he did himself little nesting sites. Behle (1958) summarized the credit" (Demille 1926). This attitude may history of the seven cormorant colonies of account for the fact that the cormorant is which he was aware. At the time of his

This manuscripl was prepared in partial fulfillment of the requirements for the degree of Master of Science in Zoolojjy at Brighi Young University. Provo, L'tah. The research was supported in part by a grant from the National Audubon .ScK-iety.

PO. Box 28147, San Ant( Great Basin Naturalist Vol. 37, No. 1

writing, all but two (Egg Island and Bear River) had been deserted or destroyed (Fig.

1). In addition I found a reference to an unreported colony located on White Rock, a small island located a few hundred yards northwest of Antelope Island, Great Salt Lake. A set of cormorant eggs was collected from there on 10 May 1901 (Woodbury et al. 1949). I also discovered an unreported colony located west of Bountiful in 1973. Behle (1958) did not mention Utah Lake as a nesting area, and it is mentioned only once in the other literature as a "former" nesting site (Woodbury et al. 1949). How- ever, I was able to find unpublished references that included a record of four cormorant eggs collected in Provo Bay in 1920 (Bee 1920). Cottam (1927) stated that the Double-crested Cormorant nested on Utah Lake. 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 active cormorant nests 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

V/Be« March 1977 Mitchell: Cormorant Biology

The water depth in this area varies from a fornia Gulls {Larus californicus) nested on few milhmeters to 2 m and averages about the dike itself. 1 m. The principle vegetative types are hardstem buHrush (Scirpus acutiis), tamarix Methods and Procedures (Tamarix petandra), cottonwood {Populus fremonti), and willow (Salix amygdaloides). The study began in the spring of 1972

The third colony is located 11 km north of and continued until the spring of 1974. Provo Bay at the United States Steel Com- Two blinds were set up at the Geneva pany Geneva Works and is designated Gen- Colony to allow observation of nesting ac- eva Colony (Fig. 2). tivity. Both blinds were set up on the east

The Springville Colony is located 0.5 km bank of the Geneva pond. One blind was due west of the mouth of Hobble Creek in placed opposite trees 1 and 2 about 12 m a stand of cottonwood trees that range from distant (Fig. 3). Six cormorant nests were 10-20 m in height and extend in a straight visible from this blind. Tree 3, which con- line west from the shore into the bay. The tained three cormorant nests, was also ob- tree line, which is about 0.5 km long, was servable when binoculars were used. The established in the late 1930's during low second blind was placed about 300 m far- lake levels. The westernmost trees are dead, ther north near the northeast corner of the in 1 m of water, and in 1971 and 1972 the pond. Tree 4 was about 30 m away, and trees most distant from shore were used by nine cormorant nests were observable when cormorants for nesting. In 1973, apparently binoculars or a spottingscope were used. due to increased numbers, the birds moved All trees were mapped, and each nest eastward into some living cottonwoods that was assigned an identification number. In had previously been used exclusively by order to determine reuse of old nests and Great Blue Herons {Ardea herodias) for the number of new nests built, the nests nesting. that remained intact from the previous year

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 stand of cottonwoods and willows growing in an east-west line in about 0.6 m of water. In 1971 the area consisted of 18 trees ranging from 10-20 m in height. In 1973 cormorants nested with Great Blue Herons in one cottonwood and in four willow trees Primary Dike (1.2 km) at the east end of the tree line.

The Geneva Colony is located on a diver- sion dike, built in 1940, that extends about 1.2 km within the reservoir. This artificial pond is located west of the steel plant proper and is about 0.2 km from Utah

Lake. The water is contained by 3 m high earthen walls (Fig. 3). The water, which is over 6 m deep in most places, is used for cooling purposes in the steel-making pro- cess. The cormorants nested in one cottonwood and three Siberian elms {Ulmiis pii- mila), all living, at the distal end of the dike. Great Blue Herons, Snowy Egrets {Leucophoyx thula), and Black-crowned Fig. 3. Map of Geneva reservoir showing the loca- Night (Nycticorax nycticorax) nested Herons tion of the bhnds and the trees containing cormorant in the same trees, while thousands of Cali- nests. Great Basin Naturalist Vol. 37, No. 1 were mapped before the birds returned. Ob- fication. Weight was determined using three servations of the eggs and young in the Sargent- Welch dial spring-balances: a 250 nests were made using four ahiminum poles, gm balance accurate to 2 gm, a 500 gm 1.5 cm in diameter and 1.6 m long, which balance to 5 gm, and a 2000 gm balance to could be inserted into one another and se- 10 gm. A small linen bag was attached to cured by a wing nut. A side-view mirror at- the balance hook to hold the bird for tached to the end pole afforded a view of weight readings. The bill and tarsometa- the nest. When held at chest level, this as- tarsus lengths were measured with a clear semblage allowed visual access to most plastic 150 mm rule. The bill was measured nests. Tape was placed at 0.2 m intervals from the corner of the mouth to the tip of on the poles to measure nest height from the upper mandible. The tarsometatarsus ground or water level. was measured from the point of articulation One new and one rebuilt nest were col- below the ankle to its articulation with the lected from the Springville Colony for fau- middle toe. nal examination in Berlese funnels and for In 1973 trips were made to all recorded comparative measurements of numbers, av- nesting sites in the state to determine which erage thickness, and length of each piece of colonies still existed and to conduct a cen- nesting material. Invertebrates found in the sus of Utah's cormorant population. The nests were collected for identification. colony at Bear River Migratory Bird Refuge Egg length and width were measured us- was visited in order to photograph the use ing dial calipers accurate to one-twentieth of an alternative nesting habitat and to de- (.05) of a millimeter. Measurements were termine location and size. Letters were also made to compare eggs of the same clutch, sent to managers of selected state bird ref- eggs within the colony, and eggs from dif- uges in an attempt to discover new breed- ferent colonies. Egg volume was determined ing colonies. using the formula V = 0.526 LB^, where L = longitudinal axis and B = transverse Results axis (Romanoff and Romanoff 1949). and Discussion Average clutch size was determined for each colony by including abandoned nests, Breeding colonies of cormorants in Utah but not unused nests. A nest was considered have been reported in Cache, Rich, Millard, abandoned if it contained at least one egg Box Elder, and Davis counties. The only at any time, but showed no signs of in- published reference to breeding in Utah cubation for one week. Nests that never County was a brief mention of the area as a contained an egg were considered unused. "former" nesting site (Woodbury et al. Hatching success for each breeding pair 1949). This paper, then, is the first detailed was determined by dividing the number of report of the nesting of the cormorant on hatchlings that survived one day by the to- Utah Lake, Utah County. tal number of eggs laid in the nest, and for On 20 June 1973 I visited the Newstate the colony by the total number of hatch- Gun Club located 4 km west of Bountiful, lings that survived one day by the total Davis County, Utah. An unreported cormo- number of eggs laid in the colony. rant breeding colony was located with nests Fledgling success was determined for the in Russian olive (Elaeagnus angustifolia) Geneva Colony by dividing the total num- trees along the south side of the Burton ber of fledglings that left the nest by the Canal. About 15 trees, averaging 8 m high, number of hatchlings that survived one day. were scattered for 1 km along the canal. Three measurements— weight, length of They contained 42 active nests with 66 bill, and tarsometatarsus— were made daily well-developed young. In addition, 23 im- of the Geneva hatchlings to determine mature birds were seen swimming in the growth rates. A number indicating nest and canal. The trees containing cormorant nests order of hatching was written on tape and also held a total of 61 Great Blue Heron attached to the leg of each bird for identi- nests with young. The caretaker of the March 1977 Mitchell: Cormorant Biology

property reported that the cormorants had competition for nesting space may not re- nested there since 1962. quire an early return. Arrival at Nesting Sites.— In 1972 the It may also be that the birds in each col- first birds to return to the Springville Colo- ony remain associated at their wintering ny were seen on 4 March. Cormorants were grounds and return as a group, or that the first seen at the Bay Colony on 13 March individual birds are site specific. Color-

and at the Geneva Colony on 22 March. In banding fledglings to determine if they re- 1973 the first cormorants were seen at the turn to the same colony each year may help Springville Colony on 7 March and on 14 answer this question. March at the Bay Colony. Three birds, seen Nest Construction.—The Double-crested

on 26 March, were the first to arrive at the Cormorant utilizes two different nesting sit- Geneva Colony. uations determined by local conditions. Of the thirteen colonies reported in this paper, Lockerbie (1942) stated that over a peri- seven were ground-nesting colonies and of od of years the earliest observation dates for these only the Bear River Colony is still in cormorants in Utah was 29 March. The existence. Vermeer (1973) stated that cor- earliest that cormorants have been seen at morants prefer to nest on the ground and Bear River Refuge is 5 March (Behle 1958). nested in trees only after their ground nest- The arrival of cormorants on 4 March 1972 ing habitat was disturbed. However, this is at Springville during this study is the not always the case, since the birds at Ge- earliest record for Utah. neva could have nested undisturbed on the In 1972 and 1973 the first returning birds dike in association with California gulls, but encountered inclement weather conditions, instead nested in trees. and some ice remained on Utah Lake. It is Most cormorants that nest along the At- interesting to note that the first birds re- lantic coast nest at ground level on islands turned to the Bay Colony a week later than bare of vegetation (Bent 1922; Lewis 1929; the Springville birds. Yet, all of the birds Mendall 1936). Townsend (Bent 1922) found that nested at the colonies Bay and Geneva that these island nests consisted of seaweed, returned within four weeks, while birds kelp, grass, and a few sticks. The nest di- were still arriving at the Springville Colony mensions averaged 52 cm across by 12 cm in Since the and building nests late May. deep. first cormorants to return to Springville are Unlike the flimsy nests described by often subjected to extremely poor weather Townsend (Bent 1922), Lewis (1929), and conditions, their early arrival must provide Mendall (1936), Behle (1958) found that the with adaptive advantage. It may them some ground-nesting cormorants at Egg Island that since it is the largest colony, nesting be built elaborate interwoven nests of sage and space is at the first birds to a premium and greasewood twigs. The twigs averaged 12 to return are assured of the choicest areas. I 18 mm thick and 290 to 580 mm long. The observed that those birds that did not return nests were built on or near rocks and some Springville until in were to May 1973 of the nest cups were lined with gull feath- forced to build their nests west of the main ers. Nests that had been used for more than cormorant colony. one season were almost cemented solid with The reason for the time difference in re- excrement. Cormorants did not nest on the

turn to each colony is puzzling. The Bay islands at Bear River Refuge until three

Colony is subjected to essentially the same years after the islands were built (Marshall type of weather conditions as Springville. 1937). At that time rocks were placed at Geneva may have somewhat different each end of the islands and cormorants then

weather, but the pond is always ice-free so used them for nesting. Yet, Behle (1958), the birds could obtain food at any time. Lewis (1929), Mendall (1936), and Munro The Bay and Geneva colonies are consi- (1927) report nesting on bare ground in derably smaller in numbers of nesting birds comparable island situations. than the Springville Colony, so the lack of Nest Utilization.— Of the 83 cormorant 6 Great Basin Naturalist Vol. 37, No. 1

nests located in the Springville Colony in 1973, 14 (17 percent) of the nests left from the previous year were utilized by the first returning birds. In the entire colony only five nests were destroyed and two abandoned. The height of the nests averaged 5.2 m (range 2.4 to 7.6 m) above the surface of the water. The nests per tree varied from 1 to 11. There did not seem to be any corre- lation 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. Of the seven cormorant nests studied at the Bay Colony during the nesting season, none were lost, although two nests were abandoned. The nest height averaged 5.3 m (range 4.3 to 6.4 m). Nests per tree varied

from 1 to 3. All nest-building ceased by early April. In 1972 cormorants nested in four trees on the dike at the Geneva Colony (Table

1). 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. 3). Eighteen nests from the previous year were reused, 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. One nest each in trees 2 and 4 were lost when they fell out of the trees during a storm. The same trees used for nesting at Ge- neva in 1972 were occupied in 1973. How-

ever, tree 1 was utilized first in 1973, fol- lowed 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 (33 percent) of

Table 1. Summary of nest utilization at the Geneva Colony indicating numbers of new and rebuilt nests in each tree used for nesting. The number in parentheses indicates the percent of total colony nests each tree contained. March 1977 Mitchell: Cormorant Biology wide. Reused nests tend to increase in size each year, due to the addition of material. The nest cup was hned with finer materials, 7,5 including leaves and cormorant feathers. Occasionally, parts of live and dead bull- rushes were also used to line the nest cup. One new and one rebuilt nest were collected for comparison of building materials. The new nest had materials averaging 312 mm in length (range 150 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 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 {Denneste.s lardarius) and several flies {Rhegoclema sp.) were identified. These invertebrates should not be considered a de- finitive list of organisms that are found in company with cormorants. They are only examples of what may be found, as I have encountered no other list of this type in the literature.

From my observations in 1972 I con- cluded that old nests, in good condition, were the preferred nesting habitat of returning cormorants. There was an order of preference from those highest in a particu- lar tree to the lowest. Only after these were occupied were new nests built. Despite this general rule, at Geneva in 1973 new nests were built while old nests were left unoccu- pied.

There is evidence that the most mature birds arrive at a colony and begin nesting first (Lack 1968, Palmer 1962). If that were true, the higher nests in a colony may have a better hatching success, since the older birds should be more prolific and make few- er nesting errors (Lack 1968, Lewis 1929).

To test this, I took the average of all nest heights for each colony and determined the hatching success for the nests situated above the average height as compared to those below the average height. In every instance, the lower nests had a higher hatching success (Fig. 4). 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 to the ele- Great Basin Naturalist Vol. 37, No. 1 ing a colony with Great Blue Herons, cies is a behavioral adaptation for partition- Water Turkeys, and American Egrets in ing the nesting habitat to avoid interspecific Tennessee. Cormorants have also been re- collisions, which could result in the loss of ported nesting with Great Blue Herons and eggs and young. Black-crowned Night Herons in Nebraska Further research may answer important (Lewis 1931). questions related to nesting, such as whether

I have observed that when cormorants cormorants return to the same colony each nest in the same trees with herons, the cor- year or even the same tree and nest. It is morant nests are always located below the not known whether tree-nesting cormorants level of the heron nests. Stanford (1937) could effectively become ground nesters. An noted the same thing at the colony in attempt to induce the ground-nesting cor- Cache Valley. At Springville and Geneva, morants at Bear River Refuge to nest in where only one heron was nesting in a tree trees was successful when old nests were occupied by cormorants, the heron's nest placed in nest boxes in an artificial tree was the topmost in that tree. When heron made of 2 x 4's on the island in unit no. 4 nests were located at the same level as a (Gunther, pers. comm.). It also needs to be cormorant nest, the heron nests were never determined whether cormorants could be situated closer than 3 m to it. At Geneva in enticed to a new nesting area by taking old 1972 the highest nest in tree 1 was utilized nests from a former colony and placing by a Great Blue Heron. In 1973 the same them in a new location. nest was used by a cormorant, later desert- Egg Laying and Incubation.— In 1973 ed, and again used by a heron during the egg laying began at the Springville Colony same season. on 26 March and continued into late May.

Although there is no explanation in the Egg laying began at the Bay Colony about literature for partitioning of the nesting 6 April and continued into early May, and habitat by these two species, I feel this con- at the Geneva Colony began on 13 April dition may exist for two reasons. Cormo- and continued until 17 May. rants are noted for the large amount of ex- The difference in the beginning egg lay- crement they deposit outside the nest, to ing dates at each colony is a reflection of the point that the very trees they nest in the time differential in early arrivals at each are often killed (Lewis 1929; Mitchell pers. colony. There is a three-week period be- obser.). The feces could also be harmful if tween the date of first arrivals and the date they were deposited on heron eggs or that eggs are first laid, so that eggs are laid young located beneath a cormorant nest. first at Springville and last at Geneva.

However, the most probable reason is the The eggs laid on 26 March 1973 at difference in take-off and landing patterns Springville comprise the earliest record for of the two birds. The cormorant is not an Utah (Behle 1958), although Lewis (1929) agile bird and, in order to become air- stated that Utah had the earliest laying borne, must launch itself precipitously out dates for any state and theorized that laying of the nest (Hall 1926). This may result in began during the second half of March. eggs or young being kicked out of the nest. Five records from Utah, given by Townsend Likewise, when they land at the nest, they (Bent 1922), provided dates of 9 April to 17 will sometimes miss their footing and fall May for egg laying. The earliest reported out of the tree or crash into their nest-mate date for eggs laid in Utah was 28 March or other cormorants nesting nearby. In com- 1937 at Egg Island, Great Salt Lake (Behle

parison, the Great Blue Heron is able to fly 1958). Marshall (1937) reported a very late away from the nest with considerable grace egg laying date at Bear River Refuge, by launching itself straight into the air, or where nests contained viable eggs on 2 Sep- land at the nest with amazing agility so as tember 1936. to not disturb any of the nesting birds lo- Eggs were laid over a 12-week period at

cated nearby. Therefore, I feel that the Springville and over more than a 4-week stratification of the nests of these two spe- period at Geneva (Fig. 5), although the bulk March 1977 Mitchell: Cormorant Biology

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

Fig. 5. Distribution of egg laying at Geneva Colony from 14 April to 20 May 1973. of laying at Geneva came within a 2- gave the incubation period for the Eu- week period. Vermeer (1969) reported egg ropean Cormorant (Phalacrocorax carbo), laying lasted for a period of 2.5 months in though somewhat larger in size than P. a. Alberta, Canada. At Geneva 90 percent of auritus, as 28.5 days. Van Tets (1959), the females laid one egg per day until the working with the svibspecies P. a. cincinatiis clutch was complete. The other females in British Columbia, had 27 records for in- took more than a day to lay one or more of cubation, varying from 25 to 29 days, with their eggs. Others have noted that females most eggs hatching after 28 days. For the laid one egg per day until the clutch was 16 Geneva hatchlings in 1973 incubation complete (Behle 1958; Lewis 1929; Mendall varied from 26 to 30 days with an average 1936), although Lack (1968) stated, that cor- of 28 days for incubation. The difference morants lay eggs every two to three days. between the dates reported by others and Lewis (1929) and Palmer (1962) reported my results may again be due to early nest- that incubation usually began after depo- ing and cooler weather. sition of the third egg. Mendall (1926) and At Geneva in 1972, 11 nests lost one or Behle (1958) observed that incubation may more eggs before hatching. All of the eggs begin with the first egg, or at any time from four of the nests were lost before 10 thereafter, until the last egg is laid. I found May and a replacement clutch was laid for that incubation began immediately after the each by 29 May. The replacement clutch first egg was laid, which may be due to egg consisted of the same number of eggs as lost laying beginning early in Utah while the in three of the nests and one more egg than weather is still very cool. lost in the other. In 1973, 12 nests lost one The incubation periods given by Behle or more eggs prior to hatching. However, (1958), Lewis (1929), and Mendall (1936) of the seven nests that eventually lost all were 25 days. Bergtold (1917) reported that eggs, no clutch was completely lost before most North American cormorants averaged 24 May, and no new clutches were laid. 28 days for incubation, and Worth (1940) Renesting occurred in 30 to 50 percent of 10 Great Basin Naturalist Vol. 37, No. 1

cormorants in Manitoba whose eggs or nests Table 2. Numbers of eggs laid per nest at the Utah were destroyed (McLeod and Bondar 1953). Lake colonies. The percent of the totals are in paren- Double-crested Cormorants have never been theses. reported to raise two broods in a single year. It appears that as long as one of the original eggs remains in the clutch, there is no replacement of lost eggs. Also, there is apparently a period during 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 in Utah), she is unable to replace a lost ckitch. Clutch Size.— The normal clutch size of the Double-crested Cormorant is three or four eggs, with four eggs most common (Bent 1922; Davie 1900; Lewis 1929; Men- dall 1936). Palmer (1962) reported a range of two to seven eggs with one record of nine eggs. Lewis (1929) found that most cormorants along the Gulf of St. Lawrence had a clutch of four eggs, "rarely" five eggs, and 5-10 percent contained three eggs. Mendall (1936) reported the following percentages for Maine: two eggs, 8 percent; three eggs, 40 percent; four eggs, 50 percent; five 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.

I censused eggs weekly in the Springville and Bay colonies and daily in the Geneva Colony; then the maximum number of eggs present was counted before hatching began. A total of 126 eggs were found in the Springville Colony (average 3.8 eggs per nest), and 28 eggs in the Bay Colony (average 4.0 eggs per nest) in 1973. At the Gen- eva Colony in 1972 a total of 80 eggs were found (average 4.2 eggs per nest), and in 1973, 61 eggs (3.6 average) were found. The average for all the colonies in 1972 and 1973 was 3.8 eggs per nest. Table 2 indicates the combined totals and percentages of all the clutches from the Utah Lake colonies. These figures agree with other find- ings, although there is a greater percentage of clutches containing four and five eggs than previously reported. £gg Measurements.— Measurements of the longitudinal and transverse axes of the cormorant eggs indicated that the Bay Colony eggs had the smallest average length and March 1977 Mitchell: Cormorant Biology 11

Table 3. Egg measurements from various sources compared with those of the Utah Lake colonies, showing range in length and width measurements with averages in parentheses.

Date 12 Great Basin Naturalist Vol. 37, No. 1

Table 5. A random selection of 20 eggs, taken at different times and from different Utah Lake colonies, showing the volume as figured by length and width measurement compared to volume computed from weight. (Ar- ranged according to increasing weight.) March 1977 Mitchell: Cormorant Biology 13

Table 6. Summary of the egg laying and hatching success for the Utah Lake colonies.

Colony 14 Great Basin Naturalist Vol. 37, No. 1 from the nest for as long as 45 minutes, al- eggs from nests that had been vacated for though the interval was usually less. While only a few minutes (Drent and Guignet awaiting my departure, the adults flew to 1961, Van Tets 1959), and 28 percent of the the reservoir and when I left immediately eggs in the colony were lost due to these flew back to the nest. Their moist feathers predations in 1963 (Drent et al. 1964). Cali- and water on the eggs may have resulted in fornia Gulls are known to attack and con- an extended period before optimum in- sume the eggs and young of unguarded cubation temperature was again reached nests (Behle 1958, Odin 1957, Vermeer (Lack 1968). 1970). The personnel at Bear River Refuge Ricklefs (1969) has stated that high tem- informed me that they had to employ meth- perature in eggs, caused by exposure to the ods to discourage gulls from nesting because sun, is a serious mortality factor. This may they were so destructive to the eggs and have contributed to the mortality of some young of water birds, including the cormo- of the eggs in exposed nests, but may not rant. be an important factor, since temperatures There are no records of mammalian pre- were not high until the last of May, when dators on the eggs and young of cormo- 90 percent of hatching was already com- rants. Lewis (1929) reported that, even pleted. when there were large numbers of coyotes Seven of the Geneva nests that were {Canis latrans) in an area where a nesting regularly attended by the adults in 1973 colony was accessible, they were never contained only addled eggs and made up 39 known to attempt any attack. percent of all Geneva eggs. That is consid- Contrary to these reports and the state- erably higher than the 24 percent of addled ment made by Armstrong (1965) that gulls eggs reported for a colony of ground-nest- always attack eggs in vacated cormorant ing cormorants {P. a. cincinatus) in British nests, I never observed mammalian or avian Columbia (Drent et al. 1964). All nests at predation at any of the Utah Lake colonies.

Geneva that contained only addled eggs In addition, I never saw any evidence of were still being incubated by the adults two predation, such as broken eggs, ravaged weeks after the expected hatching date. young, etc., which would indicate attacks

Three of these nests were still being in- during my absence, although I anticipated cubated 30 days after the estimated hatch- serious problems from the California Gulls ing date. Incubation of addled or infertile when I disturbed the nesting birds at Gen- eggs by cormorants beyond the normal in- eva. But even when I kept the cormorants cubation period is well documented (Snow from their nests for as long as 45 minutes, 1 1960). never observed an aggressive act toward the Preckition of Eggs and Ytiing.— Predation eggs or young from a gull, although hun- on the eggs and young of cormorants is dreds were flying nearby. It is not sugges- common. Ferry (1909) observed predation ted, however, that the gulls never attack by Ring-billed Gulls {L(irits delawarensis) on cormorant eggs and young in this area. the eggs of cormorants in Saskatchewan. Food Items.— Most of the studies dealing Lewis (1929) reported predation on eggs with the food of the Double-crested Cormo- and young by Great Black-backed Gulls rant have been along the Atlantic coast {Lams tnarinus), crows {Corvus brachy- (Lewis 1929; Mendall 1936). Therefore, they rhynchos), and ravens (Corvus corax). This contain lists of marine species of fish and do only occurred when the adults were absent not provide good information on the food from the nests, since they are usually in- habits of inland cormorants. The few re- trepid defenders of their nests. Herring cords that do exist include those of the Bio- Gulls {Lams argentatus) have also been ob- logical Survey (Lewis 1929) that reported served attacking eggs and young of un- the stomachs of nine birds collected at the guarded cormorant nests (Bourget 1973; mouth of Bear River contained the follow- Mendall 1936). At Mandarte Island in Bri- ing: carp {Cyprinus carpio), 73 percent; tish Columbia, crows and gulls removed Utah Sucker {Catostomus ardens), 19 per- March 1977 Mitchell: Cormorant Biology 15 cent; Chub {Leuciscus litieatiis), 3 percent; cause of death of fledglings, very young Chub {Leuciscus sp.), 6 percent. Behle birds are also susceptible to death by expo- (1958) found the following species regur- sure during hot weather. On hot sunny days gitated by young birds at Egg Island, Great it was necessary for the adults to shade the Salt Lake: carp, catfish. Yellow Perch (Perca young, and I have observed the young die flavescens), Silverside Minnows {Richanl- within minutes when the adults were fright- sonius hydrophlox), and Webug Suckers {Ca- ened away. Of the 18 young that hatched at tostomus fecundus). Other records (Lewis Geneva in 1973, 13 survived long enough to 1929, Mendall 1936) have reported cormo- leave the nest. After they were a week old, rants eating Bluegill Sunfish (Lepomis pal- the birds were better able to move into lidus). Pumpkin-seed Sunfish {Lepomis gih- shade and employed gular flutter to cool bosus), Northern Crappies {Pomoxis themselves as indicated by Bartholomew et sparoides). Common Crappies {Pomoxis an- al. (1968) and Lasiewiski and Snyder (1969). nularis), Northern Pike {Esox lucius). Wall- eye {Stizostedion vitreum), and a mudpuppy Table 7. Reactions to human handling by Double- crested Cormorant nestlings during specific age peri- {Necturus maculosus). Palmer (1962) record- ods. ed crayfish, frogs, Fathead Minnows {Pime- phales promelas), and dace {Rhinicthys sp.) as additional food items. Age (days) Reaction Food items were obtained only from nestlings that regurgitated when I approached Can barely hold head up; no physical re- or handled them. Some items that had been sistance or escape attempts; cower and partially eaten were taken directly from the shiver when held; usually make no nest. Remains of Black Bullhead {Ictahirus sound; crawl toward shade when exposed melas). Carp, and Utah Chub {Gila atraria) were found at all three colonies; Goldfish 4-7 Head held erect to peer at intruder; {Carassius auratus) were found only at Gen- make a whining sound; cower when eva Colony, and White Bass {Roccus chry- hand reached out; attempt to hide be- nest-mates; sit quietly when head sops) only at the Springville Colony. The hind or eyes are covered. fish found ranged in size from 3 cm (goldfish) to 22 cm (bullhead). 8-13 Defecate or regurgitate food when han- Of these five species of fish the nestlings dled; peck at intruders; squawk loudly; were known to use for food, the Utah peck at nest-mate when placed back in the nest; quiet down when head is cov- Chub, White Bass, and Goldfish are report- ered. ed here for the first time. Development of the Young.— When the 14-22 Climb out of nest onto limbs away from young birds hatched they were naked, blind, intruder; defecate or regurgitate when toes and beak to hang and barely able to move, and they had a taut approached; use onto any object within reach; will not black skin, although Lewis (1929) and Men- remain quiet even when head covered; dall (1936) reported that they had a dark- peck viciously when handled. brown skin that turned black within a day or two. From about the fourth day after 23- Climb frantically out of nest when approached; often fall or jump out of nest hatching (Table 7), the oldest birds in the into water; swim well at first attempt. clutch were very aggressive. This sometimes resulted in the smaller or younger birds being deprived of food and ultimately dying of starvation (Behle 1958, Hall 1926). At The eyes opened when the birds were Geneva three birds apparently starved when about four to five days old and the egg only a few days old while their siblings tooth dropped off at four to seven days, al- grew normally and continued in good though some birds retained the egg tooth health. for as long as 12 days. A fine black down Although starvation may be the major appeared about the sixth day. Eight days 16 Great Basin Naturalist Vol. 37, No. 1 later the birds were completely covered by 20 days the Geneva young averaged 1158 down. When two weeks old, the young gm; Mendall (1936) recorded an average of were very adroit in the use of beak and feet 1232 gm. The average weight for the Gen- for grasping. When taken out of the nest, eva young after the 23-day period was 1543 they would grab onto anything with their gm (Fig. 7). Gonsiderable weight addition beak and toes, and it was difficult to dis- takes place thereafter, since Lewis (1929) lodge them. I observed a four-week-old bird gave the average weight for adult males as climb 5 m up a tree to the nest from which 2100 gm and adult females as 1670 gm. it had fallen. Those values differ from birds collected in Until about two weeks old, the young Maine where 10 adult males averaged 2233 were fed a semiliquid diet by regurgitation gm and 12 adult females averaged 1861 gm from the adults. Thereafter, whole or par- (Kury 1968). The Utah birds are even larger tially digested fish were brought to the nest. than those in Maine. Four specimens taken

At i 7 to 19 days the flight feathers first ap- from Springville in 1974 averaged 2247 gm peared along the alar tracts, and the light- for two females, and 2553 gm for two colored gular pouch became a deeper yel- males. low. The young were fully feathered at Other than the averages recorded at eight weeks and were easily recognizable on hatching, there is no additional information the water or in flight by their brownish for beak measurements and tarsometatarsal backs and cream-colored breasts, in contrast growth in the literature. When 23 days old, to the glossy black of the adults. the young had an average beak length of 73 Measurements of the Young.— Three mm and an average tarsometatarsal length measurements of the nestlings in accessible of 58 mm. Palmer (1962) records the aver- nests at Geneva Colony in 1973 were taken age tarsometatarsal length of adult birds as in order to determine growth patterns. Due 61 mm. Measurements of an immature cor- to the low hatching success, only 16 young morant (BYU Life Sciences Museum) in- were available for measurements and three dicated a beak length of 89 mm and tarso- of those died within four days. Each bird metatarsal length of 58 mm. The was weighed daily and linear measurements relationship of these measurements to the of the beak and tarsometatarsus taken. Fig- growth patterns values are indicated in ures 7, 8, and 9 contain summaries of these Figs. 8 and 9. The growth curve of the measurements. beak indicates continual increase through The average weight at hatching was 36 the 23rd day, but the tarsometatarsal length after the gm (Fig. 7), and tarsometatarsal length was levels out at approximately 57 mm 11 mm (Fig. 8). This is close to Lewis's 19th day. (1929) measurements of 37 gm and 12 mm, Nest Departure.— There is little agree- respectively. Mendall (1936) reported an av- ment among authors as to when young cor- erage weight at hatching of 32 gm. The av- morants first leave the nest and how they erage beak length of the Geneva birds at accomplish their departure. Some, but not hatching was 17 mm (Fig. 9), but Lewis all, of the variation can be explained by the (1929) reported an average length of 11 difference in nest location, such as nesting mm. The discrepancy is due to different on low islands, on cliffs, or in trees. Towns- measuring techniques. I measured along the end (Bent 1922) noted that the young re- side of the beak from the corner of the mained in tree nests until fully feathered mouth to the tip of the upper mandible, and flew at about eight weeks of age. How- and Lewis measured from base to the tip ever, if they fell into water before they along the top of the beak. The average could fly, they would make no attempt to weight for Mendall's (1936) birds at five swim. Lewis (1929) reported that the young days was 158 gm, and mine averaged 156 stayed in tree nests until about six weeks gm. At 14 days Lewis (1929) reported an old, when they made their first flight. Men- average weight of 778 gm, Mendall report- dall (1936) observed that young birds flew ed 785 gm, and mine averaged 736 gm. At feebly to the water from cliff nests at six March 1977 Mitchell: Cormorant Biology 17 weeks of age, but were not able to dive un- Great Salt Lake, were observed to swim til seven weeks old. Lack (1968) stated that and dive long before they were able to fly, cormorants remained in the nest until they although no age was noted for either event could fly and did not swim until after they (Behle 1958). In contrast. Burns (1921) were able to fly. Cormorants on Egg Island, found that the young usually fell, rather 18 Great Basin Naturalist Vol. 37, No. 1 than flew, into the water from nests in order to increase the distance between them trees. Some of these birds were only 17 and me, which often resulted in young birds days old when they fell from the nests. falling into the water. At first I suspected

I observed that very few tree-nesting cor- that they had drowned, but I later observed morants in Utah remained in the nest until them swimming as far as 15 m underwater. they were able to fly. After the young were After a large number had fallen out of the approximately three weeks old, they would nest they could be seen swimming in groups leave the nest and move onto tree limbs in some distance from the colony. I presumed

Fig. 8. Mean increase in tarsometatarsal length (mm) from measurements on alternate days. The vertical line represents the range, the horizontal line the mean, and the blackened area is equal to two standard deviations.

The sample size is given at the top of each day's measurements. March 1977 Mitchell: Cormorant Biology 19

that my presence caused early departures three and six weeks of age swimming in the until I visited the colony at Newstate Gun canal. I satisfied myself that they were not Club in June 1973. At the time of my visit able to fly by chasing them up and down the birds had not been disturbed for three the canal. While I was there, other young weeks, yet when I arrived at the colony fell into the water and two birds that fell there were 23 immature birds between onto the ground immediately walked over

Fig. 9. Mean increase in beak length (mm) from measurements on alternate days. The vertical line represents the range, the horizontal line the mean, and the blackened area is equal to two standard deviations. The sample size is given at the top of each day's measurements. 20 Great Basin Naturalist Vol. 37, No. 1

to the canal and swam away. Early depar- morants for over 50 years (Bee 1920), al- ture from the nest would require the young though it has received little attention. The to learn quickly to fish or to continue to be population there has at times exceeded 300 fed by the adults (Behle 1958, Lewis 1929, nesting birds (Bee 1949). Smaller numbers Mendall 1936). I have never observed of cormorants have nested in the Geneva young cormorants being fed on the water, Colony but have probably done so contin- but I assume the adults continue to feed uously for almost 30 years (Bee 1946). The them until they are able to fish effectively total number of cormorants breeding in the for themselves. Utah Lake area for the past five years has The dates stated below pertain to the probably remained stable at around 100 time when the birds were sufficiently devel- nesting pairs, although the numbers utilizing

oped to be absent from the nest and prob- each colony fluctuate (Table 8). ably survive. This does not imply that the birds were able to fly when they left the Table 8. Numbers of active nests in the Utah Lake nest. all In observed cases the birds fell or colonies over a five-year period. jumped from the nest into the water and

swam expertly away. This made it impos- sible to estimate the date when the fledg- Year

lings 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 six 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. Migration.— Most of the local cormorants leave the Utah Lake area in October. Al-

though 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

Louisiana by 1 December. An unusual sighting was made by Reed Ferris in 1959 (Scott 1959) when he saw a

cormorant at Geneva reservoir on 1 Janu-

ary. Since the reservoir is supplied with

warm water, it does not freeze during the

winter and the bird would be able to fish. However, there was no way to tell whether the bird was a late southern migrant, a bird that had overwintered, a very early arrival, or an injured bird.

Discussion

Status of Utah Lake Colonies.— Provo Bay has been a major nesting site for cor- March 1977 Mitchell: Cormorant Biology 21

region were threatened with extinction. Table 10. Summary of Utah's existing cormorant Sugden (1936) noted an alarming decrease population as of 1973. in the numbers of herons and cormorants nesting on the Great Salt Lake and made a plea for their protection. Of the 13 colonies that have existed at one time or another within the state, only five were still in use in 1974 (Table 9). Dur- ing the 1930s and 1940s the larger colonies may have easily supported a combined total population of well over 1000 birds. How- ever, in 1973 the total known cormorant population of Utah consisted of only 386 birds nesting in five colonies (Table 10).

Table 9. Summary of the populations of Utah's cormorant colonies and their current status. 22 Great Basin Naturalist Vol. 37, No. 1

1949. Unpublished field notes, 6:93-106. Life Marshall, W. H. 1937. Double-crested Cormorant Sciences Museum, Brigham Young University, nesting on the Bear River Refuge in Utah. Con- Prove, Utah. dor 39:36. Behle, W. H. 1935. history of the bird A colonies of McLeod, J. A. and G. F. Bondar. 1953. A brief study the Great Salt Lake. Condor 37:24-35. of the Double-crested Cormorant on Lake Win- 1958. The bird life of Great Salt Lake. Univ. nepegosis. Can. Field Nat. 67:1-11. Press, Salt Lake. Mendall, H. L. 1936. The home life and economic Bent, A. C. 1922. Life histories of North American status of the Double-crested Cormorant {Phaia- petrels and pelicans, and their allies. U.S. Nat. crocorax auritus auritus Lesson). Univ. Maine Mus. Bull. 121:236-261. Studies, Second Ser., No. 38, Maine Bull. 39(3). Bergtold, W. H. 1917. study of the incubation A pe- Munro, J. A. 1927. Observations on the Double- riods of birds. Kendrick-Bellamy Co., Denver. crested Cormorant (Phaiacrocorax auritus) on BoiRGET, A. A. 1973. Relation of eiders and gulls nest- Lake Manitoba. Can. Field Nat. 41:102-108. ing in mixed colonies in Penobscot Bay, Maine. Odin, C. R. 1957. California gull predation on water- Auk 90:809-820. fowl. Auk 74:185-202. BucHHEisTER, C. W. 1944. The comeback of the cor- Pagnalli, C. v., a. Olzowka, and A. Ar. 1974. The morants. Audubon 46:14-29. avian egg: surface area, volume, and density. Burns, F. L. 1921. Comparative period of nesting life Condor 76:319-325. of some North American Nidicolae. Wilson Palmer, R. S. 1962. Handbook of North American

Bull. 33:90-99. birds I. Yale Univ. Press, New Haven. CoTT.\M, C. 1927. Distributional list of the birds of Pearson, T. G. 1927. A-birding in Utah. Bird-Lore Utah. Unpublished master's thesis, Dept. of Zo- 29:379-383. ology, Brigham Young University, Provo, Utah. Preston, F. W. 1968. The shape of birds' eggs: mathe- D.-vviE, O. 1900. Nests and eggs of North American matical aspects. Auk 85:454-463. birds. David McKay, Philadelphia. Preston, F. W. 1974. The volume of an egg. Auk B. 1926. 91:132-1,38. Demille, J. Birds of Gaspe County, Quebec. Auk 43:510-514. Rahn, H. and a. Ar. 1974. The avian egg: incubation Dre.nt, R. time and water loss. Condor 76:147-152. H. and C. J. GuiGNET. 1961. A catalogue of British Columbia sea-bird colonies. Occas. Pa- Ricklefs, R. E. 1969. An analysis of nesting mortality pers Brit. Columbia Prov. Mus., No. 12. in birds. Smithsonian Contr. Zoology, No. 9. A. L. A. Drent, R. H., G. F. Van Tets, F. Tampa, and K. Romanoff, and J. Romanoff. 1949. The Vermeer. 1964. The breeding birds of Mandarte avian egg. Wiley and Son, New York. Island, British Columbia. Can. Field Nat. Scott, O. K. 1959. Great Basin, Central Rocky Moun- 78:208-263. tain Region. Audubon Field Notes 13 (3):311- 312. Ferry, J. J. 1909. Birds observed in Saskatchewan during the summer of 1909. Auk 27:189-190. Smith, F. 1911. Double-crested Cormorants breeding Ganier, a. F. 19.33. Water birds of Reelfoot Lake. in central Illinois. Auk 28:16. J. Tenn. Acad. Sci. 8:65-83. Snow, B. 1960. The breeding biology of the Shag Gu.nther, L. 1974. Manager of Bear River Migratory (Phaiacrocorax aristotelis) on the Island of Lun- Bird Refuge. Personal communication. dy, Bristol Channel. Ibis 102:554-575. S. colonies in Hall, R. E. 1926. Notes on water birds nesting at Stanford, J. 1937. Cormorant and heron Pyramid Lake, Nevada. Condor 28:87-91. Cache Valley, Utah. Proc. Utah .\cad. Sci., Howell^ A. H. 1911. Birds of Arkansas. U.S. Biol. Arts, Letters 14:195. Surv. Bull. 38:15-16. Stoddard, H. L. 1922. Bird notes from southern Wis- KuRY, C. H. 1968. Differences in weight of male and consin. Wilson Bull. 24:67-71. 1936. Sanctuaries of the bird islands of female cormorants. Auk 85:113. Sugden, J. W. Lack, D. 1968. Ecological adaptations for breeding Great Salt Lake. Auk 53:289-294. birds. Methuen and Co. Ltd., London. Van Tets, G. F. 1959. A comparative study of the re- Lasiewiski, R. C. and G. K. Snyder. 1969. Response productive behavior and natural history of three to high temperature in nestling Double-crested sympatric species of cormorants (Phaiacrocorax Cormorants and Pelagic Cormorants. Auk auritus. Ph. penicillatus. Ph. pelogicus) at Man- 86:529-540. darte Island, B. C. Unpub'ished master's thesis,

Lewis, H. F. 1929. The natural ni. .ory of the Double- Univ. British Columbia

' •.• ' crested Cormorant {Phaiacrocorax aurittii aur- Vermeer, K. 1969. Coloni ; oi . .hlc Cormo-

itu.s Lesson). Ru-.Mi-Lou Books, Ottawa. rants and White Pi .i. .i" e { n. Field 1931. .additional information concerning the Nat. 83:.36-39.

" Double-crested Cormorai t (Phaiacrocorax aur- 1970. Some aspe. - h nes'; .. Double-

itus auritus Lesson). Auk 1 .5:207-214. crested Cormorant., a, ^^, Saskatche-

Lockerbie, C. W. 1942. Bird ,•. about the Great Salt wan, in 1969; a plea t. r ,)roteccion. Blue Jay Lake. News Bull. Mi^ieralogical Soc. Utah, 28:11-13. 3:fv4-66. 1973. Great Blue Heron and Double-crested March 1977 Mitchell: Cormorant Biology 23

Cormorant colonies in the prairie provinces. 1949. Annotated checklist of the birds of Utah. Can. Field Nat. 87:427-4.32. Bull Univ. Utah 39(16) Bio. Ser, 11(2): 1-40. White, C. Professor of zoology, Brigham Young Uni- Worth, C. B. 1940. Egg volume and incubation peri- versity, Provo, Utah. Personal communication. od. Auk 57:44-60. Woodbury, A. M., C. Cottam, and J. W. Sugden.