QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online June 16, 2004
Journal of Experimental Biology 207, 2649-2662 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01067

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Wilson, R. P. Articles by Urquhart, H. Search for Related Content PubMed PubMed Citation Articles by Wilson, R. P. Articles by Urquhart, H.

Antennae on transmitters on penguins: balancing energy budgets on the high wire

Rory P. Wilson^1,*, Jan M. Kreye¹, Klaus Lucke² and Heather Urquhart³

¹ Institut für Meereskunde, Düsternbrooker Weg 20, D-24105 Kiel, Germany
² Forschungs- und Technologiezentrum Westküste, Hafentörn, D-25761 Büsum, Germany
³ New England Aquarium, Central Wharf, Boston, MA 02110, USA

View larger version (22K): [in a new window]   Fig. 1. Schematic diagram of the system used for measuring antenna drag showing details of the relationship between antenna and pressure transducer and the attachment of the measuring system to the penguin model (inset).

View larger version (10K): [in a new window]   Fig. 2. Relationship between pressure measured by the drag measurement system shown in Fig. 1 and the torque calculated by hanging known weights at specific distances from the fulcrum (see text).

View larger version (15K): [in a new window]   Fig. 3. (A) Relationship between recorded pressure and swim speed for essentially rigid antennae of various dimensions and set at various angles to the direction of water flow mounted on a model penguin. (B) Relationship between recorded pressure and swim speed for highly flexible antennae of various dimensions and set at various angles to the direction of water flow mounted on a model penguin. White symbols, length=200 mm; grey symbols, length=150 mm; black symbols, length=100 mm.

View larger version (12K): [in a new window]   Fig. 4. Relationship between recorded pressure and swim speed for rigid antennae (length 200 mm and set at an angle of 90° to water flow) with differing diameters mounted on a model penguin.

View larger version (24K): [in a new window]   Fig. 5. (A) Frequency distribution of swim speeds used by nine Magellanic penguins swimming from a colony at Punta Norte (N=8302). (B) Swim speed and dive depth over three consecutive dives made by a Magellanic penguin foraging from Punta Norte, Argentina. Note that the first and last dives in the series show gradually changing speeds during the dives whereas the second dive shows an abrupt change in speed (marked by an arrow) associated with a similarly abrupt change in depth, which we assume is due to prey capture (see Simeone and Wilson, 2003).

View larger version (21K): [in a new window]   Fig. 6. Frequency distribution of the number of consecutive dives (black bars; N=302) where Magellanic penguins (N=25) foraging from Punta Norte, Argentina, were considered to be exploiting a prey patch (this being defined by higher swim speeds; see text) and the frequency distribution of the amounts of estimated food ingested per patch for Magellanic penguins (grey bars; N=4 birds for 65 patches) foraging from Punta Norte, Argentina. Note that these two data sets were not derived from the same birds (see text).

View larger version (16K): [in a new window]   Fig. 7. Frequency distribution (N=60) of the time between prey patches for four Magellanic penguins foraging from Punta Norte, Argentina. The inset shows all data for periods up to, and including, 6 h, to highlight the bimodality of the data, whereas the main graph shows only those data for up to and including 120 min, to show more detail. Note that these data do not include periods where birds presumably rested overnight.

View larger version (20K): [in a new window]   Fig. 8. (A) Drag (for calculations, see text) induced by antennae of various dimensions on a model penguin as a function of swim speed. (B) Power output needed to drive antennae of different dimensions attached to the body of a penguin through water at various speeds.

View larger version (14K): [in a new window]   Fig. 9. Power input (energy expended per second) for a swimming Magellanic penguin as a function of drag. This was derived by using a polynomial fit for the mass-specific power requirements as a function of swim speed for Humboldt penguins given by Luna-Jorquera and Culik (2000) (Equation 9 in text) and then regressing these power-requirements against the drag experienced by the penguins swimming at the corresponding speed. The drag–speed relationship was determined from the standard formula (Equation 10 in text), which incorporates a drag coefficient of 0.03 (Bannasch, 1995) and a cross-sectional area of 0.018m2 (see text).

View larger version (20K): [in a new window]   Fig. 10. (A) Relationship between energy expended per second and speed for a Magellanic penguin swimming unequipped (bottom line) and equipped with antennae (flexible or stiff) of various dimensions. (B) Relationship between the cost of transport and speed for a Magellanic penguin swimming unequipped (bottom line) and equipped with antennae (flexible or stiff) of various dimensions. The arrows show the speeds at which costs of transport are minimized for the various scenarios.

View larger version (15K): [in a new window]   Fig. 11. Relationship between foraging efficiency (dimensionless) and prey capture speed for a Magellanic penguin foraging according to the conditions set out in the text. The upper line (closed circles) shows the efficiency for an unequipped bird while the lines delineated by squares and diamonds show the efficiency of birds transporting external antennae (200 mmx3 mm) at cruising speeds of 1 m s–1 and 1.77 m s–1, respectively. The formula used for the antenna-derived drag was Fd=0.913v2–0.91v1.5+ 0.183v0.5+0.014 and is the best-fit curve (r2=0.99997, F=10946, P<0.0001) from the data corresponding to the relevant antenna (see Fig. 8A). Note that the model assumes that birds encounter a prey patch once every 36.3 min, travelling at a mean speed of 1.77 m s–1, which corresponds to a patch separation of 3.86 km. Thus, swimming at 1 m s–1, patches with the same spatial distribution are encountered less often (only once every 64.25 min), although the overall foraging efficiency rises. Arrows show the approximate scenarios expected for Adélie and Magellanic penguins due to their different prey capture speeds (see text).