July• 397 1961] ADRENAL AND THYROID WEIGHTS IN BIRDS FRANK A. I•ARTMAN AND t•ATItARINE A. BROWNELL LITTLE studyhas beenmade of the relative sizesof adrenaland thy- roid glandsin different speciesof birds. One of us (Hartman, 1946) reported such a study on birds collectedin the United States some years ago. In this paper, resultson birds collectedin Panamainclude a numberof familiesand speciesnot found in the United States, some migrants from the United States, and two domesticspecies, Gallus gallus and Coturnix coturnix. Data from 249 speciesin 49 familiesare reported. Specimenswere obtained during Decemberand January near sea level on the Rio Chagresand during February and March at 1,300 meters elevation near the villageof E1 VolcAnin the Provinceof Chiriqui. This material was also usedto study the musclesof locomotionas well as to furnish skins of the rare forms. METHODS All specimenswere kept in plastic,waterproof bags to preventdrying until weighed at the field station. Small birds were weighed on a torsionbalance of 120 gramscapacity. Larger oneswere weighedon Chatilion spring balances,the most sensitiveone for the weight in- volved being used: 6,000 grams capacitywith 24 grams sensitivity; 500 gramscapacity with 10 gramssensitivity; and 250 gramscapacity with 5 grams sensitivity. The adrenalsand thyroids were carefully dissectedfree of extraneoustissue with the aid of a binocularloupe and promptlyweighed on a Roller-Smith balanceof either 30 mg. or 1,500 mg. capacity,depending upon the size of the specimen.The thorough- ness of the dissectionis extremely important becausemore or less extraneoustissue may adhereto the gland,especially the adrenal,thus contributingto the error. Only birdsof healthyappearance were used. Most birds were collected between 0700 and 1100. RESULTS Mean body weightsand weightsof adrenal and thyroid glandsas percentagesof body weightsare given in the table. The numberof individualsof eachspecies is indicatedin parentheses.Additional data on speciesin which the numberof individualsis too smallfor inclusion in the table are listed in the text. Speciesare arrangedaccording to Peters' Check-List (Peters, 1931-1951) or Eisenmann'sList (Eisen- mann, 1955). 398 HARTMANANI) BROWNELT., ,4drenal and Thyroid 14/eights I[Vol. Auk78 I,•dividual Yariation There was great range amongthe individualsof many speciesill both adrenal and thyroid weights,perhaps more often in the adrenalsthan in the thyroids. It is this factor that makes it difficult to determinethe typical mean unlessa large seriesis available. However, somespecies do not show this wide range. These are: Anhinga, Snowy Egret, Cattle Egret, Least Bittern, Broad-wingedHawk, Barred Forest Fal- con,Jaqana, Scaled Pigeon, S1nooth-billed Ani, LineatedWoodpecker, Red-crownedWoodpecker, Lineated Foliage-gleaner,Red-capped Manakin, TurquoiseCotinga, Bright-rumped Attila, Masked Tityra, StreakedFlycatcher, Yellow-rmnped Cacique, White-lined Tanager, and Thick-billed Seed Finch. ,4 dr enals The adrenalsare largerthan the thyroidsin 176 species,while the reverseis true in 42 species,the remainderbeing nearly the same. With a largernumber of samplesthese values might change somewhat but neverenough to reversethe picture. For representativespecies of eachfanlily, adrenal weights are plotted against body weight in Figure 1, the speciesstarred in Table 1 beingemployed. It will be notedthat the adrenalweights of birdsweighing 200 grams or lessare essentially a lin- ear functionof bodyweight, whereas larger birds show a greatdiver- gence,a fewbeing below the line but more being above. The relatively largestadrenals were found in the OlivaceousCormorant, Barred Forest Falcon,Scintillant Hummingbird, Green Kingfisher, Pygmy Kingfisher, Red-headedBarbet, Red4aced Spinetail, Bright-rumped Attila, Scale- crestedPygmy Tyrant, Yellow Tyrannulet,Rough-winged Swallow, SouthernHouse Wren, Olive-backedThrush, Scrub Greenlet. and Red- leggedHoneycreeper. In a few speciesthe adrenalswere relatively rather small. Thesewere the AmericanJaqana, some pigeons, Fiery-billed Arac.'ari, Momotus subrufescens,Golden-olive Woodpecker, Lineated Woodpecker, Fasci- atedAntshrike, and CrestedOropendola. No sexdifferences were noted, nor wasa significantdifference found in birdsthat were collected with an egg in theoviduct ready to belaid. Thyroid Thyroidweights for representativemembers (the same species as for adrenals)of eachfamily are plotted in Figure2 asa functionof body weight.A'lthough the general trend is linear,unlike the adrenals, thereis greater divergence allalong the line, Small species diverging as much as large ones. 399 Julyl1961] HARTMAN^•D BROWnELl.,•tdrenal and Thyroid Weights 40000 ZOO00 6000 4000 1000 5O0 300 20 I I f I I I • I I I I I BODY 5 •0 20 30 50 70 I 0 200 400600 tOO0 2000 grams Figure l. Selected plottings of adrenal weights against body weights. The relatively largest thyroids were found in the CommonEgret, Violet Sabrewing, Scintillant Hummingbird, Pale-breastedSpinetail, Rough-wingedSwallow, White-throatedRobin, Long-billedGnatwren, Green Honeycreeper, Black-throated Green Warbler, Pileolated Warbler, Rose-breastedGrosbeak, and Yellow-faced Grassquit. The relatively smallestthyroids were obtainedfrom the Anhinga, Broad- winged Hawk, Brown-hoodedParrot, Barn Owl, Common Potoo, Col- lared Aragari, and Golden-olivel¾oodpecker. Occasionallyone thy- roid was much larger than the other, so much so that the smaller of the two appearedas a mere fragment. This differenceappeared to be much less common in the adrenals. Data from a number of speciesthat appearedto differ in adrenal or thyroid size have been analyzed statistically,using Student's t test 400 HARTMANAND BROWNELL, •4drenal and ThyroidI47eights tVol.[ Auk78 40O 20O 5OO 300 200 •PARULIOAE 3 to 2o 30 50 70 i0.0 zoo 4 0 2000 BODY grams Figure 2. Selected plottings of thyroid weights against body weights. (Student, 1908). The adrenals of the White-throated Crake were larger (P<0.05) than thoseof the Gray-neckedWood Rail. The adre- nals of the Scaled Pigeon •vere smaller (P%0.05) than those of the Rufous-breastedQuail Dove. The adrenalsof the S1nooth-billedAni •vere larger (P%0.05) than those of the Greater Ani. The adrenals of the Yello•v-rumpedCacique •vere larger (P%0.01) than thoseof the Crested Oropendola. The adrenals of the Gray-breasted Martin (P%0.05) and the Spot-cro•vnedWoodhe•ver (P%0.01) were smaller than those of the Red-legged Honeycreeper. The adrenals of the Common Bush-tanager were larger than those of the White-lined Tanager (P%0.01), Rose-breastedThrush Tanager (P%0.05), Vari- able Seedeater(P%0.01), and the Thick-billed Seed-finch(P%0.01). DISCUSSION In this survey it shouldbe noted that there •vas an absenceof any manifestationsof diseasein the specimensincluded and that they •vere collectedmostly in the morning hours during •vhich they had been Julyl19611 HARTMANA•) BROWNELL,•4drenal and Thyroid Weights 401 feeding. This was also done at the time of the year when most of them were not breeding. A few were northern migrants. In those speciesthat show great individual variation, large numbers are required to demonstratewhether there are differencesin the adre- nals or thyroidsdue to sex, season,or climate. Latimer (1924) found no sexdifference in the adrenalsin an extensivestudy of White Leghorn chickensat different ages. Riddle (1925) reportedan increasein the sizeof the adrenalof pigeonsand dovesat the time of ovulation. How- ever, he used closelyinbred strains in a controlled environment. Rid- dle (19'27) also found that pigeon thyroids were largest in autumn and winter and smallest in the summer. In an earlier paper by one of us (Hartman, 1946), data were re- portedfor 79 speciesin 12 familiesthat are not coveredin this study. The rangeof variationfor both adrenalsand thyroidsin somespecies was as great as we find in this study. Among all speciesincluded in this and the previouscommunication few showedgreat distinctionin the relativesize of the adrenals. None are relativelyas large as those of the Brown Pelican,those of the Barred Forest Falconbeing next in relativesize. It is also interestingto note that the adrenalsand thy- roidsin Panam/•migrants from the United Statesshowed no significant differencefrom the glandsin the samespecies collected in the summer in the United States. This was true for the Black-and-WhiteWarbler, the Black-throatedGreen Warbler, the Chestnut-sidedWarbler, and the Rose-breastedGrosbeak. However, we do find differences in a few Panam/• and Florida birds. The adrenals of the Olivaceus Cormorant were larger than those of the Double-crestedCormorant collected in Florida. The reversewas true for the thyroids. This inverserelation- ship betweenadrenal and thyroid weightsbrings to mind Harris' (1955) discussionof the reciprocalrelation betweenthyroid and adrenal cortical secretion in mammals under the control of the anterior pituitary. As he pointsout, this Occursparticularly in responseto stressfulsituations when the adrenalsecretory activity increasesand that of the thyroiddecreases. However, there was no evidenceto indi- cate that the OlivaceusCormorant group had beensubjected to any greater stress than had Double-crested Cormorants. On the other hand,the thyroidswere larger (P<0.01) in the CommonEgret col- lectedin Panam/[compared with thosein the samespecies from Florida. That speciesof the same family may differ greatly in relative adrenalsize is shownby the Snowy Egret in the Ardeidae,the White- throatedCrake in the Rallidae,the Rufous-breastedQuail Dove