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Population cycles and bird rejuvenation

Predicting and identifying the causes of a good bird population is very complex. Several causes have to coincide to bring on a bad year.

  • The small rodent populations (voles/mice) probably have the strongest impact. These go in cycles. If there are plenty of rodents, the predators eat them and are less interested in the chicks. From time to time, the rodent populations crash and then the forest chicks get eaten up. If it has been a really good rodent year, there are many predators so when the crash comes, there is a lot of pressure on the remaining food.
  • The bird eggs hatch in mid-June. For 1-2 weeks after hatching, the chickens survival depends on the weather/temperature so they do not get cold or wet (and then freeze to death).
  • The weather also affects insects/larvae and their activities which is important since they are practically all that the chicks eat during the first month.

In optimal conditions, the chickens can eat as much as they like while staying in terrain where they are hidden from predators. The worst possible combination is wet weather and poor access to insects. The worse the conditions are, the more the chicks have to run around and chase insects in open terrain and thereby expose themselves to predators.