Breeding in this species shows the weird and wonderful side of the males . This National Geographic video shows just what makes them so unusual when they are displaying their dominance. This display is also what gives the Hooded seal its name.
Hooded seals are sexually dimorphic animals (Andersen et al., 2014) which is best demonstrated in the hood of the males. The hood inflates during times of excitement but in times of extreme excitement they can blow the nasal septum out through one of the nostrils and produce a red balloon that is demonstrated in the video above. This inflatable nasal sac also only develops in the males and is what is found inside of the hood. This development starts at around 4 years old and becomes fully developed in sexually mature bulls at about 12 years old (Blix, 2005). The males use their hood to show dominance and scare off other males so, the bigger the hood, the better the chance that they will get to mate with females. If the males have evenly sized hoods, then other methods may be used to show dominance as seen in the video above. As well as being sexually dimorphic, the Hooded seals are also size dimorphic, with adult males being approximately 1.5 times larger than females (Tucker et al., 2009).
These ice-breeding seals breed in the pack-ice off the east coasts of Canada (The Gulf, the Front, Davis Strait) and off the island Jan-Mayen in the Greenland Sea (Folkow et al., 2010). They breed very late in the pack-ice season, when the ice is slightly mobile because the pack is disappearing but tend to select heavier ice than other species of pinnipeds. The Hooded seal mothers gather in recognizable herds but have greater distances between individuals than in other species such as Grey or Harp seals and it is normal for them to be spaced at 50 to 100m intervals. They gather in these dense aggregations in isolated locations which is thought to have developed evolutionarily as an anti predator strategy (Lydersen and Kovacs, 1999).
The Greenland stock assemble in late March in dispersed colonies along the pack-ice edge where they will give birth to only one pup (Folkow et al., 2010). This normally happens at the center of a large heavy ice-floe and while the female attends to the pup she will be courted by at least one adult male, but usually more (Blix, 2005). The female Hooded seals chose large ice floes when they are available in the Gulf of St. Lawrence and actively move considerable distances away from the edges of the ice into central areas.
Once born, the pup is weaned when it is only 4 – 5 days old which is the shortest time of any mammal. After this the pup must fend for itself (Folkow et al., 2010). Pups weigh 25-30kg at birth and while they are with their mother for the brief 4 – 5 days, their growth rate can exceed 7kg a day (of which approximately 70% is blubber) increasing to about 45kg at weaning (Blix, 2005). The females on the other hand will lose between 8 and 10kg a day while fasting during this period (Iverson et al., 1995). The pups are able to gain this much weight and reserves because pinniped milk has very high fat content with values recorded at 61%, which is the highest value reported for any mammal (Puppione et al., 1992). This enables the pup to build up a large amount of reserves in the form of a blubber layer, enabling it to learn to fend for itself once it has been weaned.
This next video should give you a good idea of just how fast these pups grow, and the reasons behind the extremely short lactation period