Energetics of diving in macaroni penguins

Abstract

SUMMARYHeart rate (fH), abdominal temperature (Tab) and diving depth were measured in thirteen free-ranging breeding female macaroni penguins. Measurement of these variables allowed estimation of the mass-specific rate of oxygen consumption (V̇O2) while diving and investigation of the physiological adjustments that might facilitate the diving behaviour observed in this species. In common with other diving birds, macaroni penguins showed significant changes in fH associated with diving, and these variables accounted for 36% of the variation in dive duration. When V̇O2 was calculated for dives of different durations, 95.3% of dives measured were within the calculated aerobic dive limit (cADL) for this species. Mean fH for all complete dive cycles was 147±6 beats min-1. When this fH is used to estimate V̇O2 of 26.2±1.4 ml min-1 kg-1 then only 92.8% of dives measured were within the cADL. Significant changes in abdominal temperature were not detected within individual dives, though the time constant of the measuring device used may not have been low enough to record these changes if they were present. Abdominal temperature did decline consistently during bouts of repeated diving of all durations and the mean decrease in Tab during a diving bout was 2.32±0.2°C. There was a linear relationship between bout duration and the magnitude of this temperature drop. There was no commensurate increase in dive duration during dive bouts as Tab declined, suggesting that macaroni penguins are diving within their physiological limits and that factors other than Tab are important in determining the duration of dives and dive bouts. Lowered Tab will in turn facilitate lower metabolic rates during diving bouts, but it was not possible in the present study to determine the importance of this energy saving and whether it is occurs actively or passively.

Behavioural flexibility during year-round foraging in macaroni penguins

“…Data were extracted from 67 data loggers and prepared and analysed using purpose-written computer programs within the SAS statistical package (Version 8.2, SAS Institute). As in previous work (Green et al 2002(Green et al , 2003, the recovery period following the implantation period was excluded from the analysis by either (1) ignoring data collected during the period from implantation to the start of the first foraging trip for birds receiving implants during the chickrearing period, or (2) ignoring data collected during the first 52 h for birds receiving implants during fasting periods (Green et al 2002). Careful observation of the breeding behaviour of the individual penguins and preliminary analysis of the depth and body-attitude data allowed each day of the deployment for each penguin to be assigned to a phase of the annual cycle and a day since the start of that phase for that bird.…”

“…The DLs used in the present study were designed by one of the authors (A. J. Woakes) and were the 2 newest versions (Mark 3a, Mark 3b) of an instrument previously used to study diving behaviour of macaroni penguins (Green et al 2003). Mark 3a instruments were used for all deployments during the 2001-02 season.…”

“…In all analyses, dives were treated as independent events. While accepting that this assump-tion may not be strictly correct, it is necessary in order to perform further statistical analyses (Green et al 2003).…”

“…Several studies have examined behaviour during the summer breeding season, when the penguins are constrained by the requirement to return to land regularly (Williams & Croxall 1991). These include studies of energetics (Davis et al 1989, Green et al 2002, foraging location (Barlow & Croxall 2002b), diving behaviour (Croxall et al 1993, Green et al 2003, nest attendance and chick-rearing and diet (Barlow & Croxall 2002a). However, macaroni penguins spend over half the year, including the entire austral winter, at sea, apparently without returning to land (Williams & Croxall 1991).…”

“…In all analyses, dives were treated as independent events. While accepting that this assump-185 Mar Ecol Prog Ser 296: [183][184][185][186][187][188][189][190][191][192][193][194][195][196] 2005 tion may not be strictly correct, it is necessary in order to perform further statistical analyses (Green et al 2003).As discussed by Tremblay & Cherel (2003), a variety of criteria have been used to distinguish foraging and non-foraging (travelling or searching) dives in penguins. In their study of the congeneric rockhopper penguin Eudyptes chryscosome, Tremblay & Cherel (2003) identified an important and well defined mode at ≤ 5 m in the distribution of dive depth and chose this as their criterion to define foraging and non-foraging dives.…”