Longevity of the American Herring Gull

Home , American herring gull, Herring gull, Lapwing

188 MARSHALL,Longevity of theAmerican Herring Gull L[Auk April

maleswere obtained. From the larval, nymphal, and especiallyfrom adult charactersthe ticks were found to constitute a new species, Ornithodorosaquilae Cooley. This form is closelyrelated to O. talaje (Guerin-Mdndville,1849) and O. kelleyi Cooleyand Kohls 1941,and can easily be confusedwith them. The adult stagesof this tick have not been found in nature. Other ectoparasitescollected in this study were of little or no significance; they were not found so frequentlynor so consistentlyon all speciesof raptorial birds as were the Ornithodorosaquilae. Of these the MallophagonDegeeriella fusca (Nitz.) was the secondmost consist- ent form collected.

LITBRATITRB CITI•D BAI•RO, W. J. 1944. Ticks and other parasites attacking Northern Cliff Swallows. Auk, 61: 413-414. CooL•Y, R. A. 1944. Ixodes ozarkus n. sp. and Ornithodoros aquilae n. sp. with notes on O. talaje and O. kelleyi (Ixodoidae). Jottr. Parasitol., 30 (No. 5); 287-294. THOMAS, RIJT}I HARRIS 1941. Ticks affecting birds' eyesigl•t. Auk, 58: 590-591. WEBSTIeR, HAROLD M. 1944. A survey of the Prairie Falcon in Colorado. Auk, 61: 609-616. WORTH, C. BROOKt{ • 1942. Ticks affecting birds' eyesight. Auk, 59: 576-577. WORC•STI{R, P. •. 1945. (Personal communication.) ./u•lea• Alaska

LONGEVITY OF THE AMERICAN HERRING GULL

BY HUBERT MARSHALL THE longevityof birds has long been a subjectof popular inter- est as well as a problem of biologicalimportance. Prior to the last decademost longevity recordswere, of necessity,bgsed on birds in captivity sincereturns from banding operationshave only recently made possiblean accurateestimate of the longevityof birds in their naturalhabitats. Gurney (1899),Mitchell (1911),and Flower (1926, 1938) have compiledrecords of the agesattained by birds in captivity and have attemptedto evaluatethe reliability of the many claims to extreme age set forth in the literature of the last several centuries. From their compilationsit is apparent that individual passerinebirds occasionallylive for 20 years and that larger birds live on rare occasionsto 50 or even80 yearsof age. All three writ- Vol.64] •947 -• MARSHALL,Longevity o[ theAmerican Herring Gull 189 ers agreethat the oldestbird, the record of which is beyonddispute, is a EuropeanEagle-Owl (Bubo bubo) which lived in captivity not lessthan 68 years. Extreme as this age may seem,Flower (1938) is prepared to accept the record of a Griffon Vulture (Gyps [ulvus) which lived for 117 years,although he notesthat this record is not beyond question. These recordsgive some estimateof the extremes of arian longevity,but the massof the data make it clear that, even in captivity,individuals of mostspecies have not been known to live greatlyin excessof 10 to 20 years. In the past 25 yearsmany North Americanspecies have been banded in sufficientnumbers to provideadequate data on the maximum as well as averageages reached by birds in the wild. The present paperpresents a reviewof the literature on the maximumage reached by the Herring Gull (Larusargentatus), both in captivityand in the wild, and presentsa studyof the averagenatural longevityof the American Herring Gull (Larus a. smithsonianus).--Theauthor is indebtedto ChandlerS. Robbinsfor manyhelpful suggestionsand to FrederickC. Lincoln who has read the manuscript. POTENTIAL LONGEVITY Potentiallongevity is the maximumage reached by any individual of a species,irrespective of the environmentalconditions under which it lived. Amongbirds the greatestrecorded ages arc almostinvar- iablyfound among individuals kept in captivitywhere adequate food and protectionfrom extremesof weather,as well as from prcdators, usually assurea far more optimum environmentthan is obtained by birds in the wild. Hence, it is no accidentthat the oldest Her- ring Gulls wcrc reared as pets of in zoos. Pearson(1935) has recordedthe oldestHerring Gulls so far rc- portcd-apair whichlived for 49 and 45 yearsrespectively and wcrc survivedby threedescendants, all morethan 30 yearsof age. The youngerbird of the pair, the female,accomplished the further un- expectedfeat of layingeggs every season for 49.consecutive years (Gross,1940). Othergulls have lived almost as long. Gurncy(1899) reportsone whichlived not lessthan 44 years. Richie (1935)re- portsanother which had bccnin captivityfor 35 yearsin 1935and which,according to Flower(1938), finally died at an ageof at least 41 years. Manyreferences to HerringGulls less than 9.5 years old arc found in the literature. Flower (1938)has calculated that the 9.0oldest Herring Gulls hc could find had lived an averageof 21 years,11 months,and of the 9_0birds, three wcrc still alive at the time his calculations wcrc made. 190 MAaS•XALL,Longevity of theAmerican Herring Gull [AukI. April

In an earlier paper,and usingall reliable sourcesof information, Flower (1926)recorded individuals of 909 specieswhich had lived six yearsor longer. Of these,609 lived overten years,137 over twenty years,and 41 over thirty years. Sincea number of Herring Gulls between40 and 50 yearsof age have been reported, it is apparent that few specieshave a longerpotential longevity. POTENTIAL NATURAL LONGEVITY Under the rigors of a. natural environment,it is to be expected that potentiallongevity would be greatlyreduced. Schiiz (1936),in a summaryof European banding records,reports the recoveryof banded Herring Gulls of 21, 22, 23, and almost25 and 26 yearsof age. Even more remarkableis the record of "Gull Dick," who for 24 years visited'the neighborhoodof Brentoh'sReef lightship in NarragansettBay where he was easilyrecognized by markings,voice, and disposition.He appearedannually and remainedin the vicinity of the lightship from October 12 to April 7, during which time he regularly ate boiled pork and fish fed him by the crew. Although he never was banded,his presencewas repeatedlyconfirmed and reported on many occasionsby MacKay (1892, 1893, 1894, 1895, 1896, 1898). The greatestrecorded age for a bandedHerring Gull on the North Americancontinent is that of No. 207898,banded in July, 1922,by W. S. McCrea on Hat Island, Michigan, and found dead by D. Mc- Donoughon BeaverIsland, Michigan, in June, 1939,after an elapsed time of almost 17 years. Since few Herring Gulls were banded in this country before 1921, it is to be expectedthat older birds will be recoveredin the future. Whether North AmericanHerring Gulls will eventuallybe found as old as thosealready recovered in Europe is a questiondepending upon differences,if any, betweensubspecies, and upon differencesin environment. The evidencenow at hand is insufficientto warrant speculationon this question. AVERAGE NATURAL LONGEVITY Averagenatural longevity lnay be definedas the meanage attained by a speciesin the wild. Few studiesof averagenatural longevity have beenattempted because it requireslarge numbersof recoveries of birds bandedas youngand subsequentlyrecovered. The Amer- ican Herring Gull admirablyfulfills this requirementsince thou- sandsof younggulls bandedat the nestingsite have been recovered and reportedto the Fish and Wildlife Servicein Washington,D. C. The assumptionson whichsuch a studyis basedhave been dis. VoL64] •947 .I MARSHALL,Longevity o! the AmericanHerring Gull 191

cussedby Farner (1945). Briefly, it must be assumedthat individuals of a specieswhich were bandedas youngand subsequentlyfound dead constitutea normal sampleof that elementof the population dying eachyear. Sinceonly a small percentageof the youngbirds are bandedeach year, and sinceonly a few of theseare recovered, the bandingreturns actually show only the averageage of thosebirds banded and recovereddead by humans. There is no reasonto sup- pose,however, that thesebirds do not representan 'averagesample of the birds dying every year; hence,the calculatedlongevity is un- doubtedlyclose to that for the population as a whole. Severalimportant considerations,however, must be taken into ac- count. While it is true that adult birds recovereddead representa fair sampleof the entire population,this doesnot apply to young birds found dead in the first severalmonths after leaving the nest. The number of recoveriesduring this period dependslargely upon whether or not the bandersrevisit the nestingisland. If the banders return, many dead chicksare recovered,giving a disproportionate weight in the sampleto thoseyoung birds which die before leaving the island. If the bandersfail to return, few recoveriesare reported during the first severalmonths of the bird's life and the sampleis disproportionatelyweighted with older birds. To avoid this diffi- culity,longevity expectancy is ordinarilycalculated from an arbitrary date (September1 in this study)when most or all fledglingshave left the nestingarea. After this date it is probablethat dead indi- vidualsof all agegroups have an equal chanceof beingrecovered. Secondly,since the numberof birds bandedvaries from year to year, the mortalityconditions prevailing in yearsof heavybanding will be unduly weightedin the populationsample. This cannotbe denied,but the data werecollected over a 25-yearperiod and hence it seemslikely that yearsof severeor of moderatemortality are dis- tributedevenly between years of heavyand light banding. And lastly,a difficultyarises from the fact that birdsdying of certain causesare more likely to be recoveredthan other birds,and that thesecauses may operate disproportionately on different age groups. Lack (1943c),for example,has shown that shootingis differential accordingto agefor boththe Black-headedGull (Larusr. ridibun- dus)and the Lesser Black-backed Gull (Larus[uscus graellsii), since theyoung birds are more easily shot. Sofew banded Herring Gulls are shotin North Americathat no provisionor correctionwas made for thisfactor. No doubtother causes of deathare disproportionately representedin the presentdata, but whetherthese are differ- 192 MARSHALL,Longevity of theAmerican Herring Gull ['AukL April

ential accordingto age or form a sizableproportion of the data is difficult to determine. The cause of death is recorded for only a minority of the recoveries,but from an inspectionof the banding returnsit seemslikely that no seriouserror arisesfrom the data being heavilyweighted with any particularcause of death. The bandingreturns used in this studyare from the filesof the Division of Wildlife Research, United States Fish and Wildlife Serv- ice. Returns were used only from birds banded as young (June, July, and August)in the yearsprior to 1940 and subsequentlyre- covereddead. September1 was selectedas the arbitrarydate from which all longevityestimates were calculated. After this date there were almostno recoveriesat the banding sites,indicating that young birds had left the vicinity and were as likely to be recoveredas any otherage-group in the population. Sincethe dataon life expectancy subsequentlypresented apply not to a natural population,but only to that portionof the populationsurviving to the first September1, it would be desirableif someestimate of the mortality betweenhatching and September1 could be made. This would enablethe calculation of the true averagenatural longevity. Certain technical diffi- culties,however, prevent its being attemptedin the presentpaper. The calculatedestimates of life expectancyas well as the age-group compositionof a stable populationof Herring Gulls are shownin Table 1. A total of 3,806 recoveries were found which met the re- quirementsof the study,a samplemore than adequatein size. Col- umns 2 and 3 of Table 1 indicate the rate at which a population of young gulls is decimatedunder conditionsof a natural environment. It is seenthat of every100 birds survivingto the first Septem- ber 1, only 40 are alive a year later, 25 two yearslater, 17 three years later, and so on until in ten yearsthe population has dwindled to almostnothing. That only 40 per centof the birdsalive on the first September1 survive for anotheryear is indicativeof the rigorsof the natural environment. Viewedin anotherlight, columns2 and 3 of Table 1 showthe age- groupcomposition of a Herring-Gullpopulation on September1, providedthe populationis stable.Thus, for every100 young there are 40 second-yearbirds, 25 third-yearbirds, and so on. Unlessthe populationis assumedto be stable,the indicatedage-group compo- sition will vary with time. Since the data were collectedover a 25-yearperiod, they would represent the averagecomposition of the populationfor that periodif an equalnumber of birdshad been bandedeach year. However,the heaviestbanding of Herring Gulls Vol.64] MARSHALL,Longevity o[ the American Herring Gull 193 •947 J wasdone between 1936 and 1939,and hencethe populationconsid- eredin thispaper is somewhatless representative of the periodbe- tween 1921 and 1935. Column 5 of Table 1 showsthe proportionof the variousage classeswhich die everyyear. It is seenthat 60 per centof the first- yearbirds and a muchlower percentage of the olderbirds--36 per centon the average--dieeach year. This trend is reflectedin the calculationof life expectancyshown in column6. Expectationof furtherlife on the firstSeptember i is 1.5 years. Thosebirds which surviveto their secondSeptember 1, however,have a further expectationof life of 2.3 years. The calculatedexpectancy for additional yearsranges between 1.9 and 2.4 years. That mortalityduring the firstyear is far heavierthan in succeedingyears indicates, undoubt- edly, the relativeinexperience of first-yearbirds as comparedwith the ability of older birds to avoid dangerand securean adequate food supply. Farner (1945),in his studyof the AmericanRobin (Turdusmigratorius), found no differencesin life expectancyin the first and succeedingyears. Lack (1943a,b, c, d.) likewisefound no importantdifferences for the EuropeanBlackbird (Turdus m. merula), Starling (Sturnusvulgaris), Song-Thrush (Turdus e. ericetorum), EnglishRobin (œrithacusrubecula melophilus), and Lapwing (Van- ellus vanellus). Several other species,however, showedimportant increasesin life expectancyfrom the first to secondyear. The Euro- pean Woodcock(Scolopax rusticola), for example,rose from 1.7 to 2.2 years; the Black-headedGull (excludingbirds reported shot), from 1.8 to 2.4 years;the LesserBlack-backed Gull (excludingbirds reported shot), from 1.8 to 2.5 years; and the European Cormorant (Phalacrocoraxc. carbo) from 1.6 to 3.0 years. All these,it will be noted, are birds of the marsh or open water. Column 6 of Table i showsthat 1.5 years is the expectationof furtherlife for thatportion of theHerring Gull populationsurviving to the first September1. Hence, to determine the longevity expectancyof this portion of the populationit is necessaryto add to 1.5 yearsan estimatedperiod equal to the time elapsedfrom the date of hatching to September1. A brief perusal of the literature (Deusing,1939) indicates that June 1 may not be too early as an averagedate for the hatchingof Herring Gulls. This would add 0.25 year to the life expectancyas calculatedfrom September1, and would indicatea total longevityexpectancy of 1.75 yearsfor thoseHerring Gulls survivingto the first September1. 194 MARSHALL,Longevity of theAmerican Herring Gull LApri•['Auk

CALCULATION OF LONGEVITY FROM MORTALITY RATE The averagenatural longevitymay be calculatedby either of two methods: (a) by calculationfrom the mean age of birds recovered dead, as is done (in modified form) above, and (b) by calculation from the ratio of young birds to adults, which in a stable popula-. tion indicatesthe annual mortality rate. The mortalityrate may be definedas the percentageof the population which diesannually. In a stablepopulation, the birds which die eachyear are replacedannually by an equal numberof young. Hence, the mortality rate is the averageratio of first-yearbirds to the total population,since the number of young alive on a given date is equal to the number of birds in the total populationwhich will die during the forthcomingyear. In the presentstudy, column 2 of Table 1 providesthe necessarydata for calculatingthe mortality rate. The ratio of youngto the total popuIationis 8,806to 8,081, or 47 per cent per year. Hence,on the average,47 per cent of the Herring Gulls alive on September1 die during the year and are annuallyreplaced by an equal numberof youngwhich survivefrom the nestingseason to September1. Burkitt (1926) provideda formula wherebythe longevityex- pectancymight be calculatedfrom the mortalityrate when he showed that Y = l/M, whereY representslongevity expectancy and M the mortality rate. Substitutingin Burkitt's formula, it is found that the longevityexpectancy of juvenileHerring Gulls living on Sep- tember1 is 2.1 years. Burkitt'sformula, however, is predicatedupon the assumptionthat mortalityis spreadevenly throughout the Sep- tember 1-August81 year; i.e., that the averagedate of death is six monthsfrom September1. Calculationof the mortalitydata by months,however, shows that mostdeaths take placein the early part of the year sincethe populationis greaterat that time and because weather conditions are more severe. The data show that the averagedate of death is slightlyless than four monthsfrom Sep- tember l, or somewhat more than two months sooner than assumed in Burkitt's formula. Applying this correctionto the answerderived by formula, a correctedlongevity expectancy of 1.9 years is deter- mined. This is 0.15 year greater than the longevityexpectancy of 1.75 yearscalculated from the mean age of birds recovereddead.

COMPARISON OF RESULTS OF DIFFERENT STUDIES In the severalstudies dealing with life expectancyand average natural longevityof birds, different arbitrary dateshave been select- Vol.•947õ47 a MARSHALL,Longevity of the American Herring Gull 195

ed from which to calculatethe age of birds recovereddead. Lack (1945a,b, c, d), for example,used August-1; the presentstudy uses September1, and Earner (1945)used November 1. The selectionof different dates doesnot necessarilyinvalidate comparisonof results betweenstudies, but severalimplications arising from this situation have not been discussedelsewhere and can profitably be mentioned here. As a general rule, the greater the period betweenhatching and the date from which life expectancyestimates are made, the greater will be the calculatedlongevity expectancyand with some species the same is true for the expectationof further life. This variation in longevityexpectancy, with changein the date froin which longevity estimatesare calculated, is due to the fact that on different datesone is dealingwith differentpopulations; i.e., the population of a specieson September1 is differentfroin what it wason August1. This differencein longevityexpectancy and expectationof further life arisingfrom differentdates froin which longevityestimates are made results from one or both of two reasons: • (a) The expectationof further life for somespecies such as the AmericanHerring Gull, Black-headedGull, and EuropeanCormo- rant is greaterat the beginningof the secondand subsequentyears of life than at the beginningof the firstyear of life. This is to say that as the bird progressesthrough the firstyear of life, its expectation of furtherlife progressivelyincreases. Hence, in studiesof such species,the later the arbitrary date from which longevityestimates are calculated,the greater will be the calculatedexpectation of furtherlife. Consequently,it is desirableto selectas earlya date as possibleand thus includein the studyas large a portionof the total population as possible. (b) Longevityexpectancy of juvenilesalive on a givendate is the sum of the expectationof further life on that date and the period elapsedbetween that date and the date of hatching. Sincethe expectationof further life doesnot ordinarily decreasewith time, the longevity expectancyincreases the later the date selected,due to the increasein the time elapsedbetween this date and the date of hatching. Hence, the later the date selected,the greater will be the calculatedlongevity expectancy. It is seenthat (a) appliesonly to thosespecies in which the expectationof further life increaseswith time and affectsboth the expectationof further life and the longevityexpectancy. On the other hand, (b) affectsonly the longevityexpectancy and applies to all 196 I•([ARSHALL,Longevity of the•lmerican Herring Gull FL AultApril species. It is suggestedthat theseconsiderations may be of assist- ance in reconcilingdifferences between studies of longevity expectancy of a specieswhen different dates are selectedfrom which esti- matesof life expectancyare made.

LONGEVITY OF NATURAL AND PROTECTED POPULATIONS Lack (1943a) makes an interestingcomparison between the life expectancyof protectedpopulations (human or laboratory-animal) and avian populations. It is known, for example, that human life expectancyin the United Statesis approximately65 years as com- pared with a potential longevity of slightly more than 100 years. Those Herring Gulls which surviveto their first September1 have a further life expectancyof 1.5 yearsas comparedwith a potential longevityof 49 years (and possiblymuch greater consideringthe in- adequacyof presentknowledge). Hence, Herring Gulls live about 3 per cent and human beingsabout 65 per cent of their potential life spans. The differencebetween average natural longevityand

TABLE I SURVIVALOF HERRING •ULLS BANDEDAS •FOUNGAND SUBSEQUENTLY RECOVERED DEAD

1. 2. 3. 4. 5. 6. Year No. alive % alive No. dying % of those Expectationof (starting at start at start during alive at start further life Sept. 1) of year of )'ear year of year dying on Sept. 1 during year (years)• 1st 3806 100 2298 60 1.5 gnd 1508 40 569 38 2.3 3rd 939 25 274 29 2.4 4th 665 17 191 29 2.3 5th 474 12 185 39 2.0 6tk 289 8 138 48 1.9 7th 151 4 59 39 2.1 8th 92 2 26 28 2.2 9th 66 2 25 loth 41 1 22 11th 19 6 12th 13 5 13th 8 4 14th 4 0 lSth 4 3 16th 1 0 17th 1 1

s Calculated by averaging, for the birds alive on each September •, the number oœ months between the selected September • and the date of death for each bird. It is assumed that all birds dying within a given month died on the •sth day of the month. Vol.•94764] .I MAgSHALL,Longevity o! the•lmerican Herring Gull 197 potentiallongevity is a roughmeasure of the severityof the natural conditionsunder which a specieslives and givessome hint of the differencein the age-groupcomposition of the two populations. An additionalcomparison is of someinterest. Column6 of Table 1 showsthat thereis little or no decreasein the expectationof further life as the Herring Gull advancesin age;i.e., a bird eight yearsold hasas much expectation of furtherlife asat anyprevious time after the first year. Hence,expectation of further life for the Herring Gull, after the firstyear, is not increasedby additionalexperience or greaterphysical maturity and seemsalmost wholly independent of the decline in vigor attendant with old age and senescence.In a humanpopulation, on the other hand, expectationof further life decreasessteadily with advancingage, after the first three years,be- causethe conditionsof modern life assurethat relatively few indi- vidualsdie before death takesits great toll in the yearsof old age and natural decline.

SUMMARY A reviewof the literature on the life expectancyof the Herring Gull revealedthat the oldestknown gull lived in captivityand died at the age of 49 years. A number of gulls which lived more than 25 yearsare mentioned. The greatestknown age for the European Herring Gull in the wild was found to be almost 26 years;on this continent the greatestrecorded age is almost 17 years. The assumptionson which a study of averagenatural longevity are basedare discussedand data are presentedwhich lead to the fol- lowing conclusions: (a) The longevity expectancyof that portion of the American Herring Gull population which survivesto the first September1 is 1.75 years. (b) The expectationof further life on the first September1 is 1.5 yearsand in succeedingyears varies between 1.9 and 2.4 years. (c) The age-groupcomposition of the Herring Gull populationis suchthat only 40 per cent of the birds surviveone year,25 per cent for two years,and only 1 per cent for ten years. The longevityexpectancy of juvenilesalive on September1 is calculatedfrom the mortalityrate and differsby only 0.15 year {tom that calculatedfrom the mean age of birds recovereddead. 198 MARSHALL,Longevity o[ theAmerican Herring Gull LAprilFAuk

REFERENCES CITED BVRK•T'r, J.P. 1926. A study of the Robin by means of marked birds. Pt. 5. British Birds, 20: 91-101. DEUSING, MURL 1939. The Herring Gulls of Hat Island, Wisconsin. Wilson Bull., 51:170-175. FARNER, DONALD S. 1945. Age groupsand longevity in the American Robin. Wilson Bull., 57: 56-74. FLOWER, STANLEY S. 1926. Contributions to our knowledge of the duration of life in vertebrate animals.--IV, Birds. Proc. gool. Soc. London, 1925: 1365-1422. 1938. Further notes on the duration of life in animals.--IV, Birds. Proc. gool. Soc. London, Series A, 108: 195-235. GROSS,A. O. 1940. Migration of Kent Island Herring Gulls. Bird Banding, 11: 129-155. GURNE¾,J. H. 1899. On the comparative ages to which birds live. Ibis, 1899: 19-42. LACK, DAVID 1943a. The age of the Blackbird. Brit. Birds, 36: 166-175. 1943b. The age of some more British birds. Brit. Birds, 36: 193-197. 1943c. The age of somemore British birds. Brit. Birds, 36: 214--221. 1943d. The life of the Robin. (H. F. and G. Witherby, London.) MACI•¾, G. H. 1892. Habits of the American Herring Gull (Larus argentatussmithsonianus) in New England. Auk, 9: 221-228. 1893. Larus argentatus smithsonianus. Auk, I0: 76. 1894. Further notes on the "Gull Dick." Auk, 1 I: 73. 1895. "Gull Dick" again. Auk, 12: 76. 1896. "Gull Dick" again. Auk, 13: 78. 1898. "Gull Dick." Auk, 15: 49-50. MITCHELL, P. CHALMERS 1911. On longevity and relative viability in mammals and birds; with a note on the theory of longevity. Proc. Zool. Soc. London, 191l: 425-548. PEARSON,T. G. 1935. A Herring Gull of great age. Bird-Lore, 37: 412-413. 1LW.•xE, J. 1935. Great age of Herring Gull: Scottish Naturalist, May-June: 69-70. ScnOz, E. 1936. Bericht (1935) der Vogelwarte Rossltten der Kaiser Wilhelm-Oesellschaft zur F6rderung der Wissenschaften. Vogelzug, 7: 68-78. (Reviewed in Bird Banding, 7: 130, 1936). ß38 West 7oth St. Chicago2t Illinois