As the weather in southern Minnesota warms and insects begin to emerge, the Arb will soon become host to a stunning group of migratory visitors. These are the wood-warblers, a diverse family of exceptionally colorful, tiny songbirds. Almost 30 species pass through the Arb during spring and fall migration. Some, such as the American Redstart and Yellow Warbler, stay here to breed; most, however, have as their final destination the boreal forest of central Canada.
Wood-warblers have their origins in the Neotropics, but over millennia, many species evolved migratory behavior in order to exploit the seasonally resource-rich regions of northern North America. Warblers typically travel in mixed-species flocks during migration, allowing them to more effectively locate food and keep an eye out for predators. On some spring mornings in the Arb when migration is in full swing, these flocks swell to extraordinary numbers; at times, the forest may appear genuinely flooded with unbelievably vibrant little birds, and the air filled with their surprisingly loud songs. In each flock, different species exploit different niches, with some such as the Northern Parula keeping to the canopy, others such as the Connecticut Warbler frequenting the understory, and others being general oddities: the Black-and-White Warbler creeps up and down tree branches, as if a miniature woodpecker.
The fact that such incredibly colorful and boldly-patterned birds exist in Minnesota comes as a great surprise to many people, even local residents. Habitat fragmentation and climate change are causing population declines in most species; therefore, increasing public awareness of their presence is vital to their conservation. So in addition to seeing Minnesota spring as a time of leaves sprouting and humid air, we should also know it as that time when the forest suddenly becomes invaded by thousands of tiny tropical birds.