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Photo © Al Tuttle

Why did my nest fail?

Nests can fail for a variety of reasons. Typically, unfavorable environmental conditions, chemical use, predator presence, and limits on food availability are the most common causes of nest mortality. Our Nest Box Troubleshooting Guide may also be helpful in determining a reason.

Additionally:

  • Poor environmental conditions can cause nest failure. Though most nest boxes have adequate insulation and ventilation, they may meet their limits during extreme weather.
  • Cold or rainy weather can also impact insect populations that birds rely on – many songbird species feed young insects exclusively. Use of chemicals such as pesticides, insecticides, or even herbicides can be a problem as well. These often affect more than just the target species; if you spray for insects, birds may ingest those insects coated with chemicals, spraying herbicides will often contaminate anything that touches that sprayed area, and even use of rodenticides has been shown to have negative effects on raptors, such as owls. It’s best not to use any of these chemicals if you wish to support a wildlife-friendly yard.
  • Starvation could occur under several situations, such as limited food availability due to adverse weather (reducing insect populations or other natural food sources) or if one parent disappears during the nestling stage. Though the other parent can sometimes make up for the for the loss by increasing their feeding rate, it’s also possible they may abandon the nest and start over.
  • Eggs can be non-viable for a variety of reasons: infertility, environmental conditions like weather or chemical use, or something that caused the eggs to be cracked. There is also an increase in the chance of infertile eggs as the breeding season progresses (in 2nd and 3rd broods) – it takes a lot of energy to create and lay the eggs.
  • There are many animals that predate bird nests, including racoons, cats, chipmunks and some other rodents, snakes, and even other birds. If you have a nest box, adding a predator guard can help increase nesting success. However, there is not much that can be done for open-cup nests, other than to follow the advice in our Code of Conduct to help avoid detection of the nest by predators.
  • Species competing for a nest box may usurp one that contains an active nest. House Sparrows and European Starlings are non-native in North America and may kill nestlings and occasionally an adult bird. Find tips on how to deal with these species here.
  • On rare occasions, severe parasite infestations can render the young so weak they cannot survive. However, just because you find mites in the nest, doesn’t mean bad news for the nest. Check out our blog to learn more.
  • Genetic disorders and chemical poisoning may result in death of the birds, but these are difficult to diagnose without lab analysis.

Unfortunately, many birds’ nests are unsuccessful in the wild, and even when monitors do everything possible to help increase those chances, there are still some things beyond our control. Rest assured this is one of the reasons why birds lay so many eggs and have multiple broods per year – they are accounting for these inevitable losses.

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Cornell Lab of Ornithology

Cornell Lab of Ornithology