It is not yet clear what the effect of corvids (such as crows, magpies and jays) on songbirds is. Corvids are known to eat the eggs and young of songbirds in the nest but when corvids are removed or when corvid numbers decline thre is not always a positive effect on songbirds.
There are a number of possible explanations for this apparent discrepancy. It may that corvids are unfairly blamed as their behaviour (they are distinctive and active in the day) makes them more easily observed than other predators.
It may also be that other predators, such as mammals or other bird species, take eggs and nestlings when corvids are absent. It could also be that corvids are simply removing individuals that would have died anyway, either in the nest or later in life (over winter for example).
Finally, it may be that songbird species differ in their vulnerability to nest predation by corvids. Previous research may not have detected an impact of corvids on songbirds because they have included songbirds whose nests are not likely to be predated by corvids.
Songbird nesting biology could influence their susceptibility to predation by corvids. For example, it could be that songbirds with smaller eggs are more vulnerable because corvids can pick up their eggs and take them from the nest.
We used previous research to find examples of nest predation of songbirds. We filtered through 5,000 research papers to find the ones which had information we could use.
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