Enstipp M R, Andrews R D, Jones D R
Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada V6T 1Z4.
J Exp Biol. 2001 Dec;204(Pt 23):4081-92. doi: 10.1242/jeb.204.23.4081.
Heart rate and dive behaviour were monitored in double-crested cormorants (Phalacrocorax auritus) during shallow (1 m) and deep diving (12 m), after breathing different gas mixtures, to investigate the role of depth and the accompanying changes in blood gas levels in cardiac and behavioural control during voluntary diving. Pre-dive heart rate in both shallow- and deep-diving birds was approximately three times the resting heart rate (137.9+/-17.5 beats min(-1); mean +/- S.D., N=5), falling abruptly upon submersion to around 200-250 beats min(-1). During shallow diving, the initial reduction in heart rate was followed by a secondary, more gradual decline, to around the resting level. In contrast, during deep diving, heart rate stabilised at 200-250 beats min(-1). In dives of similar duration, mean dive heart rate was significantly lower during shallow diving (163.2+/-14.0 beats min(-1)) than during deep diving (216.4+/-7.7 beats min(-1)), but in both cases was significantly above the resting value. The difference in cardiac response is probably due to an increase in arterial oxygen tension (Pa(O(2))) during the descent phase of deep dives (compression hyperoxia). Exposure to a hyperoxic gas mixture before shallow diving significantly increased mean dive heart rate, while exposure to a hypoxic gas mixture in both the shallow and deep dive tanks significantly reduced mean dive heart rate. In contrast, breathing hypercapnic gas before diving had no significant effect on dive heart rate. We suggest that the cardiac response to voluntary diving in double-crested cormorants is strongly influenced by changes in blood oxygen levels throughout the dive. Dive duration was unaffected by alterations in inspired gas composition, but surface interval duration decreased during hyperoxic gas exposure and increased during hypoxic gas exposure. The most efficient dive pattern (highest dive/pause ratio) was observed after hyperoxic exposure. Our study suggests that blood oxygen level is a powerful stimulus that facilitates the cardiac and behavioural adjustments during foraging that are important components of a strategy allowing double-crested cormorants to maximise the time spent under water and, hence, potential foraging time.
在双冠鸬鹚（Phalacrocorax auritus）进行浅潜（1米）和深潜（12米）时，在其呼吸不同气体混合物后，监测其心率和潜水行为，以研究深度及伴随的血气水平变化在自主潜水过程中心脏和行为控制中的作用。浅潜和深潜鸟类的潜水前心率约为静息心率的三倍（137.9±17.5次/分钟；平均值±标准差，N = 5），潜入水中后心率会突然降至约200 - 250次/分钟。在浅潜过程中，心率最初下降后会出现二次更缓慢的下降，降至静息水平左右。相比之下，在深潜过程中，心率稳定在200 - 250次/分钟。在持续时间相似的潜水中，浅潜时的平均潜水心率（163.2±14.0次/分钟）显著低于深潜时（216.4±7.7次/分钟），但在两种情况下均显著高于静息值。心脏反应的差异可能是由于深潜下降阶段动脉血氧张力（Pa(O₂)）增加（压缩性高氧血症）。在浅潜前暴露于高氧气体混合物会显著增加平均潜水心率，而在浅潜和深潜水箱中暴露于低氧气体混合物均会显著降低平均潜水心率。相比之下，潜水前呼吸高碳酸气体对潜水心率没有显著影响。我们认为，双冠鸬鹚对自主潜水的心脏反应在整个潜水中受到血氧水平变化的强烈影响。潜水持续时间不受吸入气体成分变化的影响，但在高氧气体暴露期间水面间隔时间缩短，在低氧气体暴露期间水面间隔时间延长。在高氧暴露后观察到最有效的潜水模式（最高潜水/暂停比）。我们的研究表明，血氧水平是一种强大的刺激因素，有助于在觅食过程中进行心脏和行为调整，这些调整是双冠鸬鹚最大化水下停留时间从而增加潜在觅食时间策略的重要组成部分。
