Spring is here and birds are nesting.  If you happen upon a bird’s nest, take a quick peek and then let the parents raise their young.  However, be vigilant about what you see.  During this time of year a unique parasite is also active at bird nests.  In the United States, the Brown-headed cowbird (refer below) is also active during the spring, laying it’s eggs in other birds’ nests.   At the first opportunity, when both parents are away from the nest, a female cowbird will sneak in, remove a couple of the original eggs from the nest and replace them with her own.  The nest below shows the aqua colored brown speckled eggs of the chipping sparrow.  Also included, are the larger white eggs with brown speckling.  These are the cowbird eggs that have parasitized the Chipping sparrow nest.  The cowbird eggs will hatch first and the offspring will outcompete the native nestlings by growing faster, calling louder and displaying a bright red throat patch (refer below) which attracts the foster parents to feed them more.  Many species of birds can be negatively impacted by the parasitic brood habits of the cowbird, especially forest interior species that are exposed to cowbirds due to increasing habitat fragmentation.  So the next time you see a nest, be excited and marvel at your find, but remember, there can be a lot more going on than you think.