Avian Life Cycles Research Articles

Winter preparedness safety tips

This chapter gives an overview of the consequences of photoperiodic responsiveness for the adaptability of birds to human-caused environmental change. It focuses on the question, to what extent photoperiodic responses facilitate or constrain the adaptation of avian life cycles to novel environmental conditions. Human-caused environmental changes may affect photo-responsive birds in two ways. First, the photoperiod may become an unreliable predictor of favorable conditions if the phase relationship between temperature-dependent resource availability and daylength changes. For example, advances in the timing of breeding in response to increased spring temperature expose juvenile birds to altered photoperiodic conditions, which may result in unseasonably early autumn migration. Second, range shifts and expansions may expose birds to novel photoperiodic conditions. Bird's response to the photoperiodic environment is a crucial factor determining to what extent range shifts and adaptive evolution is possible. Climate change is altering the phenology of many organisms, but at different rates. Poikilothermic organisms may immediately respond to temperature changes. In contrast, homiothermic animals, like birds, that use temperature-independent cues to time their life cycles may get out of phase with the selective environment. In environments that have suddenly changed due to human activity, photoperiodic cues might no longer lead to adaptive responses. However, if photoperiodic conditions outside a species' or population's current range elicit phenotypic changes that are favored by selection, range shifts and colonization of new habitats may be facilitated.

Response of breeding birds to mosquito control treatments of wetlands

We examined the possible effects of mosquito control treatments of wetlands withBacillus thuringiensis israelensis (Bti, applied as Vectobac-G granules) and methoprene (applied as Altosid sand granules) on wetland breeding bird communities. Data collected two years before (1988 and 1990) were compared to data collected three years after (1991–1993) treatments were applied. Total numbers of species and individuals observed remained relatively constant throughout the study period, but several individual species varied annually, most likely due to changes in water levels and habitat available. We found no effect of Bti or methoprene treatments on the bird community or on 19 individual bird species. The few differences that were observed between control and treatment were inconsistent over time and were likely due to chance because of the large number of comparisons that were completed. Despite relatively large reductions of aquatic insects (including mosquitoes) in mid- to late-summer following both treatments types, it is unlikely that food available to bird species in these wetlands was depressed during the breeding season. Effects of weather and predation were probably more important influences on species and community parameters than was mosquito control treatment during the study period. Because of lower aquatic insect densities in midto late-summer, other parts of the avian life cycle such as late summer survival, dispersal of young birds, or migrating birds may be more affected by mosquito control treatments.

Do mosquito control treatments of wetlands affect red‐winged blackbird (Agelaius phoeniceus) growth, reproduction, or behavior?

AbstractWe found no convincing evidence that reproduction, growth, or foraging behavior of red‐winged blackbirds (Agelaius phoeniceus) were negatively impacted by treatments of wetlands with either Bacillus thuringiensis israelensis (Bti, applied as Vectobac‐G granules) or methoprene (applied as Altosid sand granules). Most red‐winged blackbird parameters examined varied annually and some differences were found before treatments began. In all cases, differences found before treatments were either found again during the treatment years or no patterns existed to suggest impacts of mosquito control treatments. Only 1 of the 22 variables examined indicated a significant difference between a treatment group and the controls; males in Bti‐treated sites were larger than males in control sites during the treatment years. Clutch size indicated a significant treatment‐by‐year interaction and was higher in control areas as compared with Bti‐treated areas in 3 of the 6 years of study; 2 years occurred before any treatments were applied. Data from benthic aquatic insect studies showed that aquatic insects were depressed in wetlands treated with both methoprene and Bti in July and August. However, it is unlikely that food available to avian species in these wetlands was lower during the breeding season (May and June). Other portions of the avian life cycle that may be affected include the dispersal of young birds within or to these sites and individuals that use wetlands during migration. Impacts on these aspects of the avian community and landscape‐level effects of treatments were not addressed.