219
chapter ten
Post-partum
Daniel E. Crocker and Birgitte I. McDonald
10.1 Challenge of parturition for marine mammals
As air-breathing endotherms living in marine habitats, marine mammals have had to overcome
the problem of giving birth in an environment that is potentially challenging to a newborn.
As described in previous chapters, the marine environment presents a suite of physiological
challenges that are magnified in neonates. For example, neonates have high surface-to-volume
ratios and thin blubber layers, resulting in higher heat loss compared to adults (Chapter 9).
As a consequence of these challenges, marine mammals give birth to a single, large, precocial
young, with many species exhibiting rapid growth and development. Across marine mammal
species, offspring birth mass increases as a power function of maternal mass, called the scaling
exponent. This scaling exponent is 0.85 (using data from 58 species), indicating that smaller species give birth to relatively large offspring for their body size (Figure 10.1).
The transition to nutritional independence is a critical stage in marine mammal development and survival because young animals lack the skills and the physiology (e.g., oxygen
stores, Chapter 2) to efficiently acquire food. In mammals, lactation is the most energetically
Contents
10.1 Challenge of parturition for marine mammals ............................................................. 219
10.2 Knowledge by order .......................................................................................................... 221
10.2.1 Cetaceans ................................................................................................................ 221
10.2.1.1 Lactation strategies ................................................................................. 221
10.2.1.2 Investment ................................................................................................223
10.2.2 Pinnipeds ................................................................................................................223
10.2.2.1 Lactation strategies ................................................................................. 224
10.2.2.2 Investment and lactation metabolism ..................................................225
10.2.2.3 Mammary gland physiology ................................................................. 229
10.2.3 Sea otters ................................................................................................................. 231
10.2.4 Polar bears ............................................................................................................... 231
10.3 Toolbox ................................................................................................................................ 232
10.3.1 Mass and body condition ..................................................................................... 232
10.3.2 Field metabolic rate ................................................................................................234
10.3.3 Milk composition and intake ...............................................................................234
10.3.4 Data loggers ............................................................................................................ 235
10.3.5 Metabolism ............................................................................................................. 236
10.3.6 Detection of weaning ............................................................................................ 236
10.4 Unsolved mysteries ........................................................................................................... 236
Glossary ........................................................................................................................................ 237
References ..................................................................................................................................... 238
chapter ten
Post-partum
Daniel E. Crocker and Birgitte I. McDonald
10.1 Challenge of parturition for marine mammals
As air-breathing endotherms living in marine habitats, marine mammals have had to overcome
the problem of giving birth in an environment that is potentially challenging to a newborn.
As described in previous chapters, the marine environment presents a suite of physiological
challenges that are magnified in neonates. For example, neonates have high surface-to-volume
ratios and thin blubber layers, resulting in higher heat loss compared to adults (Chapter 9).
As a consequence of these challenges, marine mammals give birth to a single, large, precocial
young, with many species exhibiting rapid growth and development. Across marine mammal
species, offspring birth mass increases as a power function of maternal mass, called the scaling
exponent. This scaling exponent is 0.85 (using data from 58 species), indicating that smaller species give birth to relatively large offspring for their body size (Figure 10.1).
The transition to nutritional independence is a critical stage in marine mammal development and survival because young animals lack the skills and the physiology (e.g., oxygen
stores, Chapter 2) to efficiently acquire food. In mammals, lactation is the most energetically
Contents
10.1 Challenge of parturition for marine mammals ............................................................. 219
10.2 Knowledge by order .......................................................................................................... 221
10.2.1 Cetaceans ................................................................................................................ 221
10.2.1.1 Lactation strategies ................................................................................. 221
10.2.1.2 Investment ................................................................................................223
10.2.2 Pinnipeds ................................................................................................................223
10.2.2.1 Lactation strategies ................................................................................. 224
10.2.2.2 Investment and lactation metabolism ..................................................225
10.2.2.3 Mammary gland physiology ................................................................. 229
10.2.3 Sea otters ................................................................................................................. 231
10.2.4 Polar bears ............................................................................................................... 231
10.3 Toolbox ................................................................................................................................ 232
10.3.1 Mass and body condition ..................................................................................... 232
10.3.2 Field metabolic rate ................................................................................................234
10.3.3 Milk composition and intake ...............................................................................234
10.3.4 Data loggers ............................................................................................................ 235
10.3.5 Metabolism ............................................................................................................. 236
10.3.6 Detection of weaning ............................................................................................ 236
10.4 Unsolved mysteries ........................................................................................................... 236
Glossary ........................................................................................................................................ 237
References ..................................................................................................................................... 238