Most of my studies and the books I have read, indicate that 70% of Bluebird nestlings do not make it through the first year. On average, 40% die in the first 30 days after leaving the nest. This is when the fledglings are most vulnerable. After 90 days the juvenile’s chances increase. But another 30% do not make it through the first year. If I recall correctly, if they survive the first year the mortality rate drops to 20%. Now much depends on weather, availability of food, experience/age of the parents, geographic region, urban vs. rural areas, disease, pesticides and predators), etc. So the percentile varies. In general, the more physically developed the young are when they leave the nest, the greater their chances are of survival. A fledgling's chance of survival (measured by ornithologists in terms of future recaptures) increases in proportion to its mass at fledgling. The quality of parental care, the number of siblings competing for that care, and the timing of fledging are also important factors.
Bluebirds dealing with nature, life become a challenge and often the obstacles are so over whelming, but the bluebirds have met them head on; their perseverance is an example of that in the last 200 years. Of all the obstacles they must face today, a nest cavity should not be one of them. This is where conservation plays a big role. Bluebirds and other cavity Nesters rely heavily on nest boxes that landlords provide to raise their young. Install a nest box today and enjoy the gratification being a Landlord to these beautiful birds.
--- Installing A Nest Box ---
When installing a nest box, please remember bluebirds are territorial (150 yards apart) also install a predator guard on the conduit pipe (1 inch diameter) 5 or 5 1/2 feet high. your nose to the 1 1/2" hole to the nest box. Place the nest box in the most open area in your yard to help keep wrens from using the nest box. Sparrow problems see Sparrow Trap topic.