Nature on our doorsteps: Egg thieves
Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into nature on our doorsteps and the beautiful biodiversity of its plants and wildlife.
BIRDS are very busy right now as their breeding season gets underway.
Given how mild the spring has been, some species have already built their nests and are laying eggs.
If a parent bird succeeds in keeping the eggs warm and safe from predators, the fully developed chick inside will hatch. It cuts a circular jagged line around the inside of the egg and it pushes its way out.
The parent bird removes these empty shells from the nest.
Because a pile of broken eggshells accumulating on the ground below a nest would draw the attention of predators, the parent flies some distance away with the shells before dropping them to the ground.
Naturally hatched eggshells are clean inside with no hint of yellow yolk, and the broken edges are finely jagged where the chick has chipped its way out.
Eggs that have been eaten by predators look different, and often show the remains of the egg yolk and egg white inside.
Sometimes the parent bird neatly places the egg’s smaller cap inside the larger eggshell before removing them from the nest
Eggs are a rich source of protein, and so they are sought out by bigger birds and mammals who will invade the nest to feed on this rich treasure.
Magpies and Jackdaws are very quick to notice whenever a nest is being built. They watch patiently, waiting until the parent leaves the nest to feed, and in they go to steal an egg.
These predators make a small hole in the eggshell and lift the entire shell up to drain the contents directly into their beak.
Animals like Mink often bite gently along the length of the egg and then lick at the contents inside.
Foxes mostly take eggs from ground-nesting birds, and will crush the shell into smaller pieces to lap up the food.
Because eggs and chicks are so much at risk, some bird species can lay up to a dozen eggs, hoping that at least one or two chicks might survive into adulthood.
