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The effects of depth on the cardiac and behavioural responses of double-crested cormorants (Phalacrocorax auritus) during voluntary diving

Manfred R. Enstipp^*, Russel D. Andrews and David R. Jones

Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada V6T 1Z4

View larger version (10K): [in a new window]   Fig. 1. Side view and dimensions of the shallow (A) and deep (B) dive tanks. ‘F’ indicates the feeding spot, where birds picked up chopped herring pieces. The approximate underwater routes taken by the birds are indicated by the dashed lines, with the arrowheads indicating the direction of locomotion.

View larger version (46K): [in a new window]   Fig. 2. Electrocardiogram (ECG) record and instantaneous heart rate during individual deep and shallow dives of one double-crested cormorant. Top, the ECG during a deep dive; bottom, the ECG during a shallow dive. Corresponding heart rates (beats min–1) are shown in the centre. Submersion and emersion are indicated by the descending and ascending arrows, respectively.

View larger version (22K): [in a new window]   Fig. 3. Heart rate before, during and after deep and shallow diving. Values are means ± S.D. averaged over 3 s intervals from six dives per bird (all dives 18–22 s). N depicts the number of individuals used. ‘–3’ refers to the last 3 s of the dive, preceding emergence. For comparison, resting heart rate is indicated.

View larger version (19K): [in a new window]   Fig. 4. Mean dive heart rate versus dive duration for three double-crested cormorants during shallow diving (N=208). Values for each cormorant demonstrated a significant negative relationship, with r2 ranging from 0.60 to 0.84. The regression line is the average relationship for all cormorants and is described by y=257.48–5.21x, where y is mean dive heart rate and x is dive duration (r2=0.761).

View larger version (21K): [in a new window]   Fig. 5. Heart rate during resting, shallow and deep diving and after exposure to different levels of O2 and CO2. Values are means + S.D. from six dives per bird (all dives 18–22 s); the values above of the columns indicate the number of individuals used; resting heart rate was calculated from a 20 min section of ECG recording per bird. For the gas mixtures used, see Materials and methods. *Significantly different from the respective control values (air).

View larger version (23K): [in a new window]   Fig. 6. Heart rate before, during and after shallow diving following exposure to different ambient oxygen levels. Values are means ± S.D. averaged over 3 s intervals from six dives per bird (all dives 18–22 s; N=6 birds). ‘–3’ refers to the last 3 s of the dive, preceding emergence. For gas mixtures used, see Materials and methods.

View larger version (20K): [in a new window]   Fig. 7. Heart rate before, during and after deep diving following exposure to different ambient oxygen levels. Values are means ± S.D. averaged over 3 s intervals from six dives per bird (all dives 18–22 s; N=5 birds). ‘–3’ refers to the last 3 s of the dive, preceding emergence. For gas mixtures used, see Materials and methods.

View larger version (24K): [in a new window]   Fig. 8. Dive behaviour associated with shallow (open columns) and deep (filled columns) diving and after exposure to different levels of O2 (N=5 birds) and CO2 (N=4 birds). Values are means + S.D. from 10 dive cycles per bird. *Significantly different from the respective control (air) values. A significant difference between ‘shallow diving’ and ‘deep diving’.