Northern mockingbirds are altricial, meaning that, when hatched, they are born relatively immobile and defenseless and therefore require nourishment for a certain duration from their parents.
The young have a survival bottleneck at the nestling stage because there are higher levels of nestling predation than egg predation.
The levels of belligerence exhibited by parents therefore increase once eggs hatch but there is no increase during the egg stage.

A recent study shows that both food availability and temperature affect the parental incubation of the eggs in northern mockingbirds.
Increasing food availability provides the females with more time to care for the nest and perform self-maintenance.
Increasing temperature, however, reduces the time the females spend at the nest and there is increased energy cost to cool the eggs.
The incubation behavior is a trade-off among various environmental factors.

Mockingbird nests are also often parasitized by cowbirds.
The parents are found to reject parasitic eggs at an intermediate rate.
A recent study has shown that foreign eggs are more likely to be rejected from a nest later in the breeding season than from earlier in a breeding season.
Early nesting hosts may not have learned the pattern and coloration of their first clutch yet, so are less likely to reject foreign eggs.
There is also a seasonal threshold in terms of the overlap between the breeding seasons of the northern mockingbirds and their parasites.
If the breeding season of the parasites starts later, there is less likelihood of parasitism.
Hence, it pays the hosts to have relatively lower sensitivity to parasitic eggs.
Northern mockingbirds are altricial, meaning that, when hatched, they are born relatively immobile and defenseless and therefore require nourishment for a certain duration from their parents. The young have a survival bottleneck at the nestling stage because there are higher levels of nestling predation than egg predation. The levels of belligerence exhibited by parents therefore increase once eggs hatch but there is no increase during the egg stage.
A recent study shows that both food availability and temperature affect the parental incubation of the eggs in northern mockingbirds. Increasing food availability provides the females with more time to care for the nest and perform self-maintenance. Increasing temperature, however, reduces the time the females spend at the nest and there is increased energy cost to cool the eggs. The incubation behavior is a trade-off among various environmental factors.
Mockingbird nests are also often parasitized by cowbirds. The parents are found to reject parasitic eggs at an intermediate rate. A recent study has shown that foreign eggs are more likely to be rejected from a nest later in the breeding season than from earlier in a breeding season. Early nesting hosts may not have learned the pattern and coloration of their first clutch yet, so are less likely to reject foreign eggs. There is also a seasonal threshold in terms of the overlap between the breeding seasons of the northern mockingbirds and their parasites. If the breeding season of the parasites starts later, there is less likelihood of parasitism. Hence, it pays the hosts to have relatively lower sensitivity to parasitic eggs.
Northern mockingbird