<<
Home , Egg

J. Field Ornithol., 64(3):341-345

ERYTHRISTIC EGGS IN THE COMMON

HELEN HAYS American Museum of Natural History Central Park West at 79th St. New York, New York 1002d USA

KENNETH C. PARKES CarnegieMuseum of Natural History ddO0 Forbes Ave. Pittsburgh,Pennsylvania 15213 USA

Abstract.--Erythrism, an abnormallyreddish color, is known in the eggsof a few Laridae and Stercorariidae.It apparentlyresults from the absenceof one of the normal pigments and possiblyan overdoseof another.Erythrism in eggsof the CommonTern (Sternahirundo) is exceedinglyrare. Data from the long-termstudy of the large tern colonyon Great Island,New York, provideaccurate information about relative frequency of the phenomenon and demonstrateits continuityin two femaleswith changingmates.

ERITRISMO EN HUEVOS DE STERNA HIRUNDO Sinopsis.--Seha informadoeritrismo (coloraci6nrojiza anormal) en los huevosde algunas especiesde Laridae y Stercorariidae.Esta condici6nparece ser el resultadode la ausencia de uno de los pigmentosnormales y la sobreproducci6nde otro. E1 eritrismoes sumamente raro en huevosde Sternahirundo. Datos tomadosde un estudioa largo alcanceen una colonia de estasgaviotas en Great Gull Island, New York, ha provistode informaci0nprecisa sobre la frecuenciade estefen0meno y ha demonstradola continuidaddel mismoen doshembras que cambiaron de pareja.

Erythristic eggsare known in one speciesof jaeger (Stercorariuspar- asiticus),several species of (Larus), and two speciesof (Sterna) (Bates et al. 1976, Jourdain and Borrer 1914, Sutherland1980). Bates et al. explain the phenomenonas follows: "No more than two kinds of pigment are present in the eggshellsof most ..., and often one alone or practically none. One of thesepigments is blue or greenishand when presentoccurs throughout the shell structure.The other is brownish, ranging from red to black, and when presentis usuallynear the surface. A small amountmakes a white shellyellowish or pale brown and a blue shell greenor olive. The brownishpigment also produces any markings that are presentwhich may occurat variousdepths as the shellis formed, varyingin shadeaccording to their depthand the shellcolour... erythrism may be defined as having the reddish colour exaggeratedor abnormally replacing the bluish pigment." At least one early writer erroneously attributedthe reddishcolor of sucheggs to their being "stained... with blood-pigment" (Borrer 1913). Erythristic larid eggsare rare in museumcollections. Given the assid- uousnessof egg collectorsin the past, the recordsthat exist, as reviewed by Jourdain and Borrer (1914) and Bateset al. (1976), probablygive at least an approximationof the frequencyof occurrenceof this color ab- normality in this family. Publishedrecords of erythristiceggs of larids

341 342] H. Haysand K. C. Parkes J.Field Ornithol. Summer 1993 are basedon isolatedsets collected at widely scatteredlocalities as well as, in a few instances,collections made over a period of years in areasat which red eggswere found on a regular basis.For example,in the last centuryand the early part of this century,erythristic eggs of five larids werecollected at or near two localitiesalong the northerncoast of Norway (Bateset al. 1976, Jourdain and Borrer 1914). Theseincluded a number of setsof erythristicgull eggs,most of which were thoseof Gull (Larusargentatus), but alsosome of Great Black-backedGull (L. marinus). At one localityin England, red eggsof CommonTern (Sternahirundo) were found everyseason for five or six years.Borrer (1913) believedthat "a strain of birds had establisheditself in this colonywhose tendency it was to lay" red eggs,as he did not believethat the samepair of birds could have survivedand returnedfor five or six yearsto the samespot, but he was obviouslyunaware of the great longevityof CommonTerns. Bateset al. (1976), noting severalinstances in which setsof red eggsof a particular specieswere found in successiveyears at the same site, suggestedthat the samefemales might be responsiblefor thesesuccessive clutches. There are fewer recordsof erythristic eggs for terns than for gulls. Jourdainand Borrer (1914) and Bateset al. (1976) reporteda few records of erythristicsets of eggsfor Commonand Arctic (S. paradisaea)terns in Britain and Europe.A mail surveyof the institutionslisted by Bankset al. (1973) as havingthe largestegg collections in North America yielded only two erythristicsets of CommonTern eggsfrom Great Britain and one from North America. The latter, now in the San BernardinoCounty Museum, California, was collectedon 13 Jun. 1919 at North Nauset Beach,Chatham, Massachusetts.As abnormallypigmented eggs would undoubtedlyhave been selectively taken by collectors,as suggestedby the series of gull eggs from the two Norwegian localities,the paucity of erythristicCommon Tern setsin collectionsmay be taken as an indication of their rarity. Since1966, the tern colonyon Great Gull Island, Long Island Sound, New York (41ø12'N, 72ø07'W), has been intensivelystudied (Cooper et al. 1970, DiCostanzo 1980). During the breedingseason, a team of field assistantsmakes a daily searchof the 6.9 ha island, marking new and individual eggs,and banding chickson the day of hatching. A few well concealednests may be missedon thesedaily checks,but the number of these,we feel,is not significant.The numberof nests(including renests) markedper year has risen from about3000 in 1969-1982 to about6000 in 1984-1988 and 7000-9000 in 1989-1991. The thoroughnessof this surveypermits accurateestimates of the frequencyof occurrenceof any variants,such as unusual egg pigmentation. The eggsof the CommonTern are highly variablein color.The ground colorranges from off-whitethrough various shades of buff, gray, and tan to a rich olive-brown,blotched with black,gray and brown. Albino eggs are known (example,Carnegie Museum of Natural History set E-6423, two normal and one albino egg from Starve Island, Lake Erie, Ontario, Vol.64, No. 3 ErythristicEggs in theCommon Tern [343

26 Jun. 1916). Unmarked pale blue eggsare of regular occurrenceon Great Gull Island, usually one or two per year. As in the caseof the albino egg mentionedabove, the pale blue eggsare usually part of an otherwise normal clutch. One female, however, is known to have laid nothing but clutchesof blue eggsfor four or five successiveyears even though shechanged mates. This suggeststhat the female determinesthe colorand pattern of the eggs.Bates et al. (1976) notedthat femalestend to be consistentin the color and pattern of their eggsthroughout their lives, and suggesteda genetic basis for abnormal color in eggs. Our observationsof successiveclutches of blue eggslaid by one female are consistentwith this hypothesis. On 4 Jul. 1975, Parkes found a on Great Gull Island containingone erythristicegg. The next day the nest containeda secondegg, also erythristic.The eggswere laid in a scrapein weathered concrete,with no vegetation or other lining. The parents, which were never individually identified, eventuallydeserted this nest;the eggswere collectedon 20 Jul. and taken to the American Museum of Natural History, where they were preparedby Henry Pelzl and cataloguedas set 17917. Theseeggs are somewhatreminiscent of falconeggs in appearance. The backgroundis betweencolors 5 (Flesh Color) and 6 (SalmonColor) of Smithe (1975), but paler, and the spotsmatch color 132A (Brick Red) of Smithe(1981). There are no blackishor olivaceousspots, nor is there any olivaceoustone at all in the backgroundcolor. The first egg measured41.14 x 28.42 mm, the second40.09 x 28.04 mm. These measurementsare within thoseof the 82 eggsin the United StatesNational Museum measuredby Bent (1921): length35.5-45, width 27.5-32.5. No tern eggsof this particular color abnormalitywere found subse- quently on Great Gull Island until the summerof 1987, when two such setswere found. The two eggsof the first set (site A) were laid on 17 and 19 Jun., and thoseof the secondset (site B) on 6 and 7 Jul. Although there were slight color differencesamong the eggs,they all conformedto the descriptionabove. We trapped the adults at both sites and subsequentlytrapped birds associatedwith red eggs at these sites each year, with one exception, through 1991. Both of the parentstrapped in 1987 at siteA had hatched in 1984. Subsequentlythe female of this pair, sexedon the basisof bill length comparisonwith its mate (Coulter 1986), paired in 1988 with a trapped as an adult on Great Gull Island in 1983. In 1989 she paired with a bird hatched in 1984, remaining with this mate in 1990 and 1991. In 1989 and 1990 this pair had red eggs,but in 1991 they were trapped on a late nest, and the egg in the nest was brown, not red. The 1987 and 1988 mates of the site A female nested with other females subsequently.The eggsin their nestswere normal in appearance. The parents trapped in 1987 at site B were a two-year-old (hatched 1985) and a bird trapped as an adult in 1985. These birds remained togetherand were trapped on red eggseach year through 1990. In 1991 344] H. Haysand K. C.Parkes J.Field Ornithol. Summer 1993 we trapped the 1985-hatchedbird of the pair with a new mate, one that was hatchedin 1984, on two red eggs.Bill measurementsof the pair at site B in 1987 differed by only one millimeter, so we did not attempt to the membersof this pair. In 1990 and 1991 we trapped three adults that had hatched from erythristiceggs. Two had hatchedat site A, one in 1988 and one in 1989. On the basisof bill measurementthey both appearedto be females.The third hatched from the 1988 nest at the B site, and on the basis of behavior was sexedas a male. All three of these birds were trapped in 1991 on nestsin which the eggswere of normal coloration.We will continueto track the femalesknown to lay erythristic clutchesas well as their off- spring, to try to determinewhether there is any pattern of inheritanceof this colorvariant. Egg colorin the domesticfowl (Gallusgallus) has long been known to be geneticallydetermined; the blue egg shell color of the South American Araucana breed is basedon a simple autosomaldominant mutation, but the geneticsof brown eggsis more complicated(Hutt 1949). To our knowledge,erythrism has not been reported in that well-studied species. Given the apparent worldwide rarity of erythristiceggs of Common Terns, the Great Gull Island data permit an estimateof the frequency of occurrencein a large, thoroughlycensused colony. In the years from 1966 through 1991, 82,000 nestswere markedon Great Gull Island, and these nestsincluded only ten clutchesof red eggs.Of the 33,318 adult CommonTerns trapped on the island during the sameperiod, we assume half to have been females,and of these,two femaleswere responsiblefor nine of the known red eggclutches. The female parent of the clutchfound in 1975 is unknown, as the nest was not trapped.

ACKNOWLEDGMENTS

We thank the many field assistantswho have participatedin the daily checkson Great Gull Island, enabling us to follow particular nest sitesfrom year to year. We thank also the curatorsof the oologicalcollections who respondedto our request for information on erythristicCommon Tern eggs,and JosephDiCostanzo and Janet Williams for data re- trieval. We acknowledgethe Gordon RousmaniereRoberts Fund for grants for the com- puterizationof the Great Gull Island Project'sdata, and the LinnaeanSociety of New York, the American Museum of Natural History, and the mae P. Smith Fund for financial supportof the seasonsduring which data for this paper were collected.Field work of the junior author was supportedby the Edward O'Neil Fund of The Carnegie Museum of Natural History. We dedicatethis paper to the late Oliver L. Austin, Jr., a pioneerin the bandingof Common Terns, a friend, and a mentor. This is Contribution no. 68 of the Great Gull Island Project,American Museum of Natural History.

LITERATURE CITED

BANKS,R. C., M. H. CLENCH,AND J. C. BARLOW.1973. Bird collectionsin the United States and Canada. Auk 90:136-170. BATES,D. J., H. M. S. BLAIR,AND I. H. J. LYSTER. 1976. First recordederythristic eggs of Arctic Skua and Herring Gull in Britain. ScottishBirds 9:143-147. BENT,A.C. 1921. Life historiesof North Americangulls and terns.U.S. Nat. Mus. Bull. 113. Vol.64, No. 3 ErythristicEggs in theCommon Tern [345

BORRI•R,C. 1913. Exhibition of two clutchesof red eggsof the Common Tern. Bull. Brit. Orn. Club 31:112. COOPER,D. m., H. HAYS,AND C. PESSINO.1970. Breedingof the Commonand Roseate Terns on Great Gull Island. Proc. Linnaean Soc. New York 71:83-104. COULTE.R, M. 1986. Assortativemating and sexual dimorphismin the Common Tern. Wilson Bull. 98:95-100. DICOST^NZO,J. 1980. Populationdynamics of a CommonTern colony.J. Field Ornithol. 51:229-243. Huwr, F. B. 1949. Genetics of the . McGraw-Hill, New York, New York. xii -t- 590 pp. JOURD^IN,F. C. R., ANDC. BORRER.1914. Erythrism in the eggsof British birds.Brit. Birds 7:246-260. SMITHE,F.B. 1975. Naturalist's colorguide. New York, New York. American Museum of Natural History. 8 unnumberedpp. -t- 8 plates. ß 1981. Naturalist'scolor guide, part III. New York, New York. AmericanMuseum of Natural History. 57 pp. -t- 9 plates. SUTHERLAND,A. 1980. Erythristic Herring Gull eggsin Caithness.Scottish Birds 11:84. Received15 Jul. 1991; accepted18 Jun. 1992.