The change in size of bird populations is driven, like all organisms, by the ratio of births to deaths in a given time period; if the number of births are greater than the number of deaths, the population grows, if deaths are greater than births, the population declines, and if births and deaths are balanced, the population remains stable.
Many of the priority bird species that the CHJV has taken responsibility for are Neotropical migrants, or species that breed in North America, but winter from Mexico and the Caribbean south. “Births”, or the number of eggs that hatch in a given year, are a product of the number of eggs a female is capable of laying (Ruby-throated Hummingbirds typically lay 2, for example, whereas a Northern Bobwhite often lays from 12-16), as well as the number of times a female will nest throughout the breeding season. “Deaths” can, and do, occur anytime after the young hatch, and are largely a result of predation by a wide array of animals like snakes, raccoons, domestic cats, etc. but also are compounded by collisions with buildings, towers and other structures, pesticide use, and other man-made threats, or by being forced to use resource-poor areas during winter and in migration.
Relatively high rates of predation of birds on the breeding grounds in the Central Hardwoods Region typically are associated with habitat fragmentation; predation of forest birds tends to be less in landscapes with relatively large percentage of forest cover, and grassland birds typically produce more offspring if they nest in large tracts far from woody edges that serve as travel lanes and entry points for predators. Factors the CHJV takes into account in conservation planning and design, are habitat patch size and the degree of fragmentation in an area where habitat work might be targeted, as well as calculations of the total amount of habitat a species will need to achieve population objectives.
Although the work of the CHJV is directly focused on efforts to sustain viable bird populations during their breeding season in the Central Hardwoods Bird Conservation Region, in a effort to support conservation for birds throughout their life cycle, the CHJV entered into an informal partnership with the Alianza Ambiental para la Península de Yucatán (AAPY) , a group of six conservation institutions working to protect native forests and wetlands in the Yucatan Peninsula of Mexico that serve as important habitat for birds during migration and winter. CHJV partner, American Bird Conservancy, has multiple campaigns targeted to protecting habitat for Neotropical migrants, as well as reducing mortality to birds from collisions, pesticides and free-roaming cats.