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Maternal Behaviour of Humpback Whales in Southeast Alaska

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Maternal Behaviour of Humpback Whales in Southeast Alaska Maternal Behaviour of Humpback Whales in Southeast Alaska Andrew Szabo BSc., University of Victoria, 2000 A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of MASTERS OF SCIENCE in the Department of Geography 0 Andrew Szabo, 2004 University of Victoria All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author. Supervisor: Dr. Dave Duffus ABSTRACT In this study, I characterize the maternal care patterns of humpback whales in southeast Alaska. Through a study of proximity behaviour, I show that humpbacks behave similarly to terrestrial ungulate 'followers': the cow and calf are rarely more than several body lengths apart; proximity between the cow and calf is greatest during periods of travel relative to other behaviours; and, proximity is greatest when the dive behaviour of the pair is synchronized. Unlike that observed in typical follower species, however, proximity is not found to decrease significantly as the pair's association lengthens. To account for this, I argue that the length of the observation period was insufficient to detect such a trend since maternal pairs remain together for several months after the last observations. In addition, I analyze the diving behaviour of the maternal pair to examine the potential negative consequences for the female associated with the follower tactic in humpbacks. The results suggest that several behavioural modifications are made by the cow and calf in an effort to minimize the duration of separation between the two. Ultimately, I argue that behaviour observed in humpback whales is commensurate in function with following behaviour in terrestrial ungulate followers. Humpbacks are migratory, and as in many migratory species, following behaviour provides a mechanism whereby the maternal dyad can maintain close proximity during periods of travel. Moreover, as with many follower species, humpbacks can rely upon their large size as a means of defence against offspring predation. Finally, although obvious differences exist between the habitats in which humpbacks and ungulate followers reside, arguably both are open habitats that lack the cover necessary to allow for offspring concealment. TABLE OF CONTENTS . Abstract ..............................................................................................ii Table of Contents .................................................................................. v List of Tables ....................................................................................... vi ... List of Figures .................................................................................... vm .. Acknowledgements .............................................................................. x~i Introduction .......................................................................................... 1 Literature review of parental care behaviour in vertebrates .....................3 Literature review of humpback whale life history .............................. 14 Methods ............................................................................................... 21 Results ................................................................................................ 34 . Proximity Analysis ........................................................................ 34 Time Budget Analysis ................................................................. -45 Dive Behaviour Analysis ................................................................ 46 Synchrony Analysis .................................................................... -55 Discussion ......................................................................................... -61 Proximity Behaviour ...................................................................... 61 Time Budget And Dive Behaviour ...................................................69 Synchrony Behaviour .................................................................. 79 Conclusion.......................................................................................... 82 Literature Cited ....................................................................................85 Appendix ...........................................................................................-99 LIST OF TABLES Table 1. Results of Kruskal-Wallis test for differences in the frequency with which the calf iss within 0.5 body lengths (0.5BL), 1.0 body length (l.OBL), 1.5 body lengths (1.5BL) and 50m (50M) from the cow across the season and behaviours. ............................................................................... -35 Table 2. Results of Kruskal-Wallis test for differences in the frequency with which the calf is within 0.5 body lengths (0.5BL), 1.0 body length (l.OBL), 1.5 body lengths (1.5BL) and 50m (50M) from the cow across the season during travelling, foraging and surface foraging bouts.. ..................... .37 Table 3. Results of Kruskal-Wallis test for differences in the frequency with which the calf is within 0.5 body lengths (0.5BL), 1.0 body length (l.OBL), 1.5 body lengths (1.5BL) and 50m (50M) from the cow during either asynchronous or synchronous dive cycles (SYNCDIVE).................... ..39 Table 4. Results from Mann Whitney U test for differences in the frequency with which the calf is within 0.5 body lengths (0.5BL), 1.0 body length (l.OBL), 1.5 body lengths (1.5BL) and 50m (50M) from the cow between asynchronous and synchronous (SYNCDIVE) travelling, foraging or surface foraging dives.. ............................................................... .40 Table 5. Results of Wilcoxon Signed Ranks test for differences between mean cow dive duration (DIVEDUR) and mean calf dive duration (CFDIVEDUR) during travelling, foraging and surface foraging bouts in early, mid and late season.. .............................................................................. -48 Table 6. Results of Mann Whitney U test for differences in mean cow dive duration (DIVEDUR) between synchronous and asynchronous dive cycles during travelling, foraging and surface foraging bouts.. ..................... .49 Table 7. Results of Mann-Whitney U tests for differences in mean cow dive duration (DIVEDUR) between synchronous and asynchronous dive cycles during early, mid and late season observations.. .............................. ..50 Table 8. Results of Mann Whitney U test for differences in mean cow dive duration (DIVEDUR) between synchronous and asynchronous DIVE cycles during early, mid and late season observations of travelling, foraging and surface foraging bouts.. ..............................................52 Table 9. Results of Kruskal-Wallis tests for differences in the frequency of cow and calf synchrony across the season and behaviours.. ..............................56 Table 10. Results of Kruskal-Wallis tests for differences in the frequency of cow and calf synchrony behaviour across the season within travel, forage and surface forage bouts .................................................................... -58 LIST OF FIGURES Figure 1. Map of southeast Alaska. Study area includes Chatham Strait and Frederick Sound and is located approximately between latitudes 57" OO'N and 58" OO'N, and longitudes 133" 30'W and 135" OOfW........... 21 Figure 2. Four typical cow dive cycles are shown (Dive 1through 4) to illustrate SYNCDIVE synchrony and asynchrony. Diamonds represent individual surfacings for cow (upper series) and calf (lower series). Time is indicated on the horizontal axis; vertical bars are 30s apart.. ..27 Figure 3. Four typical cow dive cycles are illustrated (DIVE 1 through 4) to indicate FULLDIVE synchrony and asynchrony. Diamonds represent individual surfacings for cow (upper series) and calf (lower series). Time is indicated on the horizontal axis; vertical bars are 30s apart.. ..30 Figure 4. Four typical cow dive cycles are illustrated (DIVE 1 through 4) to demonstrate DIVE synchrony and asynchrony. Diamonds represent individual surfacings for cow (upper series) and calf (lower series). Time is indicated on the horizontal axis; vertical bars are 30s apart.. ..31 Figure 5. Frequency with which the calf is <0.5 body length (0.5BL), d.0 body length (l.OBL), <1.5 body lengths (1.5BL) and <50 metres (50M) from the cow during travelling, foraging and surface foraging bouts. Error bars represent 95% confidence intervals.. .....................................35 Figure 6. Frequency with which the calf is C0.5 body length (0.5BL), d.0 body length (l.OBL), d.5body lengths (1.5BL) and <50 metres (50M) from the cow during early, mid and late season observations. Error bars represent 95% confidence intervals.. .......................................... .36 Figure 7. Frequency with which the calf is <0.5 body length (0.5BL), d.0 body length (LOBL), d.5body lengths (1.5BL) and <50 metres (50M) from the calf within individual behaviours during early, mid and late season observations. Error bars represent 95% confidence intervals.. ......... .38 Figure 8. Frequency with which the calf is c0.5 body length (0.5BL), d.0body length (l.OBL), <1.5 body lengths (1.5BL) and <50 metres (50M) from the calf during asynchronous and synchronous SYNCDIVE travel, forage and surface forage bouts. Error bars represent 95% confidence intervals.. ............................................................................-39 Figure 9. Frequency with which the calf is ~0.5body length (0.5BL), <1.0 body length (l.OBL), 4.5 body lengths (1.5BL)
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