The animals building trade has craftsmen and cowboys too. Eager to cut corners on building costs, cliff swallows renovate and reuse last year's nests, unneighbourly shags steal materials from next door, andhermit crabs aggressively play the housing market. Expertly engineered, the most desirable dwellings boast air-conditioning, solar heating and defensive moats. But whether building a simple sandy burrow or a massive termite city, the aim of every animal architect is to keep the elements, and unwanted visitors, out.

Fight or flee? Resist or surrender? Aggression over food, territory or mates is widespread in animals. But teeth, hooves, horns and spines can cause severe injury and sometimes death. So zebras in theSerengeti, moose in Alaska and even bizarre stalk-eyed flies in Malaysia assess their opponent's prowess and choose to fight depending on what they stand to lose or gain. And despite the proliferation of weapons in nature's trials of strength, many disputes are settled without a blow being struck. Risking injury is the last resort. Written and presented by Sir David Attenborough.