Effects of environmental stressors on nest success of introduced birds

Understanding the influence of environmental stressors on daily nest survival of introduced birds is important because it can affect introduction success as well as the ability to evaluate introduction programs. For long-lived birds with low annual production, adjustment to local breeding conditions can take many years. We examined nest success rates of 2 introduced bird species, whooping crane (Grus americana) and trumpeter swan (Cygnus buccinator), in Wisconsin. Both species are long-lived with low annual reproductive rates. Trumpeter swans were established in our study area approximately 10 years before whooping cranes. We predicted that trumpeter swans would show less sensitivity to environmental stressors. We used daily nest survival rates (DNSRs) as our response variable to model several environmental parameters including weather, phenology, and ornithophilic black flies (Diptera: Simuliidae). Additionally, we examined the influence of captive history, age, release method, energetics, and nesting experience on whooping crane DNSRs. Daily nest survival of whooping cranes was the most sensitive to stressors. Trumpeter swan daily nest survival showed less sensitivity to the same stressors. Daily nest survival for both species peaked later in the nesting season, after 30 April and before 30 May. We also found that the daily nest survival rate (DNSR) for whooping cranes was potentially affected by captive exposure (measured by generations removed from the wild). Our results highlight the difficulties associated with conservation of long-lived birds with low annual productivity as they adjust to local breeding conditions and that nest phenology at the source location can determine how these conditions are interfaced. We recommend that the juxtaposition of source and introduction location nest phenology be considered prior to introduction site selection. Additionally, strategically selecting offspring from captive pairs with nest phenology similar to that of sympatric species at the introduction location should be considered.