The populations of many birds will vary significantly from year to year.
Population limitation can be caused by a number of different things such as food, nest sites, competitors, predators, disease, or harsh weather. Two of these limiters determine a carrying capacity or ceiling. These are food and nest sites. The other factors can maintain the population below the carrying capacity.
Example: experiments have been conducted on cavity nesting birds whereby they have correlated the number of birds with the number of dead trees. (Raphael and White 1984). Under a certain threshold of dead trees the birds are limited by trees. After a certain level, other factors probably limit their density.
Another few things to consider in any population of birds are their niche requirements and their habitat selection. Certain birds will choose certain habitats. .
Population regulation deals with density-dependent and density-independent
factors that prevent a population from exceeding carrying capacity.
Example: A study was done in Finland showing that temperature can regulate a population. When plotted on a graph the relationship between Great Tits (Parus major) breeding numbers and mean temperature of the preceding winters in an area of Finland can be seen.. In the winters 1969-1971. In the winters 1969-1971, extra food was provided. Filled symbols – pair numbers after winter of food provision, open symbols – pair numbers after other winters. From von Haartman 1973.
Changes in Ecological Factors as they effect Populations of birds.
Ectoparasitism and Disease: (Examples)
• Brown and Brown 1986: Cliff swallow study. The bugs per nest and bugs per nestling increased with colony size.
Ideal Free Distribution: This is very important in population dynamics. This model is the null model.
• Individuals have knowledge of all habitats
By Rob Nelson