Kingfishers are very short-lived. Many young will not have learned to fish by the time they are driven out of their parents territory. It is thought that only a half of the fledglings survive more than a week or two.
Although only a quarter survive to breed the following year, this is enough to maintain the population. Likewise, only a quarter of adult birds survive from one breeding season to the next. Very few birds live longer than one breeding season. The oldest bird on record was only 7.5 years.
Most kingfishers die of cold or lack of food a severe winter can kill a very high percentage of the birds. Despite high breeding productivity, populations can take many years to recover from a bad winter. Weather conditions in the summer can also cause significant mortality. Cold weather or flooding in the summer can make fishing difficult, resulting in starvation of the brood, while flooding can also claim many nests.
Traffic and window collisions are other known causes of death. The main predator is the domestic cat, but rats can also be a serious problem in places.
Kingfishers are high up in the food chain, and therefore extremely vulnerable to build-up of chemicals. Industrial pollution and contamination by agricultural run-off kills the fish birds rely on, effectively excluding the birds from many stretches of river that would otherwise be suitable habitats. The long-term population declines since 1970 are generally attributed to river pollution.
Human disturbance of nesting birds is a serious problem, since the broods fail if something upsets the feeding routine. If human presence close to a nest prevents these shy birds from entering the nest for too long, the chicks may weaken enough (either from cold or hunger) to stop calling. This makes the parents wrongly assume that they are well fed and will not feed them. As a result, the chicks will perish.
Heavy machinery that grades the banks and drains the land destroys many nests each year on lowland rivers. Persecution by fishermen and to provide feathers for fishing flies and to satisfy fashion trends seem to be well in the past.