constant: C = 0. 151 ± 0.0053 cal CM-2 °C. h-1(n = 29). Average weight loss for six birds (meanstarting weight was 26 ± 2 kilograms) starved in theopen for 19 days was 0.235 kilogram day-'.

It rust be stressed that the curve in the figure isincomplete. The bulk of the data was collected inJanua 1974 and the birds, therefore, were accli-mated to summer conditions. We consider the curveto bere1iminary; it will be completed in Septemberand October 1974 with winter-acclimated birds.

The field team for this study, at McMurdo Stationfrom Pctober 1973 to February 1974, included Dr.Fedak, Mr. Pinshow, Ms. Hana Pinshow, and Ms.Katherine Muzik. This research was supported byNational Science Foundation grant GV-39184A.

Emperor and Adélie penguins:energy cost of walking

MICHAEL A. FEDAK, BERRY PINSHOW,and KNUT SCHMIDT-NIELSEN

Department of ZoologyDuke University

Durham, North Carolina 27706

De pite their obvious adaptations to swimming, pen-guins spend considerable time moving about on land.Emperor penguin rookeries may be 80 kilometers fromthe sea. Since emperors travel this distance at thebeginning and end of a long fast, the energy cost ofthis trip may be important to their total energy budget.Adélie penguins also often travel long distances overland. The energy cost of locomotion in both thesebirds therefore is important to our understanding oftheir life history. Furthermore, penguins possess abody geometry that is very different from otheranimals in which the energetics of locomotion havebeen studied; this presents an opportunity to test the

generality of the conclusions drawn about the ener-getics of locomotion from studies of other animals.

During the 1973-1974 austral summer, we gathereddata on energy cost and stride frequency of walkingfrom emperor and Adélie penguins that were trainedto walk on a treadmill. The animals wore masks thatallowed us to continuously measure oxygen consump-tion while the birds ran at known speeds (Fedaket al., in press). Stride frequency was measured simul-taneously. A "stride" is defined as a complete stepcycle, from the time one foot contacts the grounduntil it contacts it again.

In both emperors and Adélies, steady state oxygenconsumption and stride frequency increased linearlywith running speed over the range of speeds thebirds maintained for 20 or more minutes. The tablelists the equations that describe these relations foreach species. By dividing the speed by the metabolicrate of a walking animal we calculate the cost oftransport for that animal. This figure tells us theamount of energy required by the animal to move oneunit of its body weight over one unit of distance.From these equations we can calculate that the costof transport for an Adélie is about twice that of anemperor. For both species the cost of transport isover twice what would be predicted for two-leggedrunning for birds of similar body weight.

The amount of energy needed by an emperor totravel the 160 kilometers to and from a rookery tothe sea is the equivalent of about 1 kilogram of fat.Since emperors may use a total of 15 kilograms offat during the fast, the travel to and from the rookerymay account for about 7 percent of the energy usedduring the fasting period.

One striking similarity between emperor and Adéliepenguins emerges from the data. Although emperorsweigh over five times as much as Adélies, the weightspecific energy cost of one stride is about the samein both species. This can be calculated by dividing the

dV02dF

slope ofby the slope of --thereby obtain-

dv dving the energy used by emperors in terms of oxygen

Oxygen consumption and stride frequency of running penguins.

SpeciesBody mass Speed range Regression equation

Emperor penguin20.79 kg 0.8<v<2.7 km h-i V02 = O.450+O.429 V(1)

F 5 = (2.2+0.99 v)103 (2)

Ad Me penguin3.89 kg 0.9<v<3.9 km h-' V02 0.940+0759v(3)

F = (4.1+1.44 v)103 (4)

V02 is oxygen consumption in 1 02 kg' h; v is running speed in km h -i ; F is stride frequency in strides per hour.

July—August 1974 97

consumed per stride. This value is independent ofrunning speed. There is only a 17 percent differencebetween the value for emperors (4.3 X 10 1 02 kg-'stride ') and for that of Adélies (5.3 X 10 10, kg-'stride-'). We are collecting stride frequency data fromother two-legged runners to see if energy cost perstride is similar in these species as well.

The field team for this study, at McMurdo fromOctober 1973 to February 1974, included Dr. Fedak,Mr. Pinshow, Ms. Hana Pinshow, and Ms. KatherineMuzik. This research was supported by NationalScience Foundation grant Gv-39184A.

Reference

Fedak, M. A., B. Pinshow, and Knut Schmidt-Nielsen. Inpress. Energy cost of bipedal running. American Journalof Physiology.

Viscous properties of bird bloodat low temperatures

GILBERT A. BLOCK and DAVID E. MuiuusHDepartment of Biology

Case Western Reserve UniversityCleveland, Ohio 44106

The blood flowing through the unfeathered feetand legs of antarctic birds experiences a large changein temperature (Murrish and Guard, 1973). Bloodmay cool from body temperature to near the freezingpoint of the tissues and then be rewarmed as it returnsto the body core. These alterations in temperaturehave a profound effect on the flow properties of theblood (Guard and Murrish, 1973). The viscosity ofwhole blood may increase three to four times astemperatures decrease from 38 0 to 0°C. The magni-tude of the viscosity change observed in whole bloodcannot be accounted for merely by the effect oftemperature on the viscous properties of water. Otherfactors present in whole blood consequently must beinvolved. The most important among them are thetotal plasma protein concentration, the volume andshape of the erythrocytes, and the hematocrit. Aspart of our continuing studies on the physical be-havior of the blood of polar homeotherms, we ex-amined the relationship of the size of erythrocytes andplasma protein concentration with the viscosity ofblood from five species of antarctic birds at varioustemperatures.

The birds used were the gentoo penguin (Pygoscelispapua), the chinstrap penguin (Pygoscelis antarc-tica), the Adélie penguin (Pygoscelis adélie), the

blue-eyed shag (Phalacrocorax atriceps), the southpolar skua (Catharacta skua mccormicki), and thegiant petrel (Macronectes giganteus). The animalsall were collected in the vicinity of Palmer Station.Blood samples were obtained in the field by veni-puncture into heparanized syringes. In the laboratory,hematocrits were determined and red blood cellcounts were made on an improved Neubauer hema-cytometer (American Optical). Measurementsof thedimensions of wet red blood cells were made vith acalibrated ocular-micrometer and the volume wascalculated from the equation for an ellipsoidS Theconcentration of total plasma protein was determinedwith the biuret method. Values for the above param-eters are given in the table. Data for apparent vis-cosity of blood at 50 percent hematocrit are fromGuard and Murrish (1973).

The two species of penguins had the greatestapparent blood viscosity observed in the five speciesat the four temperatures (fig. 1). The south polarskua and the giant petrel had the lowest apparentviscosity. Total plasma protein concentration havelittle effect on the apparent viscosity of whole bloodof antarctic birds at 38°C. As blood temperaturesdecrease, however, the apparent viscosity becomesmore dependent on protein concentration until at 0°C.the apparent viscosity of the blood from the gentoopenguin, with its high protein concentration, is 1.6times greater than that of the giant petrel.

Erythrocyte volume has little effect on aparentviscosity at 38°C. (fig. 2). The effect of a largr cell

I0 Gentoo Penguin 1 0020'— S Addle Penguin

Lo Blue-eyed Shag£ Giant Petrel

Skua

U 15>:I

£W 2001 L

5 0 __380 i

30 4.0 5.0 6.0PLASMA PROTEIN CONCENTRATION, g/100 ml

Figure 1. Relationship between total protein concentration (gproteinh1100 ml plasma) and the apparent viscosity (c.ntips.) ofblood of five species of antarctic birds. The apparent viscositywas measured at 50 percent hematocrit and at four temperatures

(Guard and Murrish, 973).

98 ANTARCTIC JOURNAL