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Right now, the whales are at the most southerly point of their travels. Why are they here? Well, these lagoons on the coast of Mexico are the perfect place for them to give birth. The water is warm and calm, and there are very few predators. But there's a big problem – while it might be a great place to give birth, there's virtually nothing for them to eat here. These mothers are effectively running on empty and are living off their fat reserves. The amazing thing is that whilst they're in the lagoons, the whales actually choose to come to boats - they feel relaxed and safe here. This is the closest encounter you'll ever get with a completely wild, enormous creature. Nobody can say for sure why they do it. Maybe it's because of the parasites - they like them scraped off, maybe it's boredom. Whatever it is, they get something out of it. Since whale watching began here, the whales have become extraordinarily trusting and inquisitive, and yet 100 years ago, grey whales were hunted to the brink of extinction. It's actually a wonderful success story. After hunting was banned, the whales made an amazing recovery. There are now probably as many greys as there were before hunting began. Grey whales are one of nature's supermums. Mother and calf have a 19,000-kilometre journey ahead of them and mum will be looking after her baby every step of the way. But right now her priority is to get her calf ready for this epic journey. The calf fuels up on mother's milk and it's awesome stuff – it's so rich, the calf puts on around 27kgs every day. Young grey whales are not strong swimmers and their mothers have often been seen getting underneath them and lifting them gently to the surface for a breather. But these youngsters need to get into training fast, and mums help here too. They'll lead their calves to the entrance of the lagoon to swim against the incoming tide in a kind of aquatic gymnasium.