National Geographic

PHOTO: ALAN MURPHY``````three types of sites: forest reserves, ex-isting subdivisions, and “changing sites”where forest was being turned into sub-division. There they caught and bandedavoider and adapter birds—nearly 3,000in all—then tracked where the birds wentand whether they fledged broods.The species studied typically staywith one mate in one area. But whendevelopment removed the low plantswhere avoiders like to nest, researcherssaw the birds relocate and “divorce,”or not reunite with, their prior mate.When finding a new partner and newterritory disrupts a breeding season,avoiders “often fail to produce young,”Marzluff says. “For a bird that lives fiveor six years, that’s a big hit.”To thrive and multiply, avoider birdswill need native habitat reserves. Butmany species of adaptable birds “dovery well around us,” Marzluff says. “It’simportant for people to realize that wecan do a lot in our yards and neighbor-hoods to foster birds.”When land developers remove nativevegetation to put in subdivisions, somesongbirds do just fine. These “adapter”species find alternative places to nestand may even thrive near humans, saysJohn Marzluff, a wildlife science pro-fessor at the University of Washington.But other species of songbirds fleein search of undisturbed habitat, evenif it means leaving a mate and losingchances to reproduce, Marzluff says. Inthe face of urbanization, the “avoider”species—such as the Wilson’s warblerabove—are known to decline.Marzluff and his colleagues spent 12years gathering data for one of the fewstudies that have been done on howurbanization affects songbird species’dispersal. The researchers identifiedMORE ’BURBS MAYMEAN LESS SEXBy Patricia Edmonds|EXPLORE|BASIC INSTINCTSWILSON’SWARBLERHABITAT/RANGEPrefer brushy, woodlandareas; breed in Alaska,Canada, and northernparts of the lower 48states; winter in thesouthern U.S., Mexico,and Central AmericaCONSERVATION STATUSThe IUCN assessment:least concernOTHER FACTSFemales and males havesimilar coloring exceptfor the males’ black cap.