Bird eggs sport an amazing variety of sizes, colors, and shapes. Their colors could fill an artist’s palette, from robin's egg blue to a buffy pink, from purple to green. When birds commonly nest in the open, their eggs may be blotched, spotted, speckled, marbled, streaked or scrawled to match their surroundings and protect them from predators. Killdeer often lay their eggs on pebbles and these are perfect rock imitations. Cavity dwellers lay pure white eggs. Camouflage is not important when the eggs are hidden in a hole. Also the parents may better see eggs in the darkness. Birds that never leave their nests like Great Blue Herons often have pure white eggs too.
Peregrine falcons nest on cliff edges and their eggs are especially pointed on one end. That way, if an egg begins to roll, it will go around in circles rather than rolling straight over the edge. Bobwhite quail eggs are pointed. Since there are so many eggs in a clutch, the pointed shape helps to fit more eggs in the nest like a jigsaw puzzle.
Cowbirds will lay their eggs into the nests of other birds to foster their young. They have done this to over 200 species of birds. Often the female cowbird will sneak into the nest when the mother is away, move or damage some eggs in the nest, and then lay her own. Cowbird eggs usually hatch first and the chicks grow quickly, enabling them to outcompete the host's chicks. There's a theory that the blue hue of eggs helps host birds pick out foreign eggs placed in their nests. According to NestWatch, some birds like the yellow warbler catch on to the deception in their nests. They may choose to build on top of the infiltrated nest. Cowbirds may in turn destroy the nest in retaliation for failing to raise their young. See a nest raid in the video below
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