1.4 A simple model for the data of Table 1.5 would be one in which each year a heron has a probability, φ say, of surviving that year. Consider whether you think this would be an adequate description of the data. What else is needed in order to be able to write down probabilities of birds being reported as dead at different ages? Records of birds reported dead in Britain have generally been declining in recent years. Why do you think that is?