Coastal lands are increasingly exposed to disturbances from demolition, beach clean-up, and construction for development. Although data exist concerning the effects of investigators on breeding populations, little information is available for migrant populations. I investigated the effects of demolition and beach clean-up on resident and migrant birds on a coastal mudflat in New Jersey. A year's censusing before work initiation was used to determine when demolition and clean-up would affect the least number of birds. Work activity on and along the beach was from 15 October to 15 November 1985. The overall population size was lower in 1985 compared to the same period in 1984, although the drop in numbers was not due solely to human disturbance. Human work activity influenced avian distribution along the mudflat: birds moved farther along the beach and out onto the mudflat when activity began, and moved back onto the mudflat when activity ceased. For gulls, foraging efficiency was lowered when work began and did not return to previous levels until 60–90 min after work began. Gulls that moved farther out on the mudflat had significantly lower foraging efficiencies than did those that remained close to the beach. Efforts to mitigate the adverse effects on birds by restricting human activity to a 100 m stretch of beach at any one time succeeded in significantly reducing adverse effects and in allowing birds some space to rest and feed.