Life History and Reproduction

Multiple studies and observations have been conducted on the American Dipper due to its unique partial-migratory activity. Unlike many other bird species, the American Dipper usually remains residential to their original territory only occasionally moving to near-by streams and rivers from time to time based on food availability and stream turbulence (BirdWeb 1999). Some American Dipper populations consist of individuals who are either migratory or sedentary/residential (Mackas et al. 2010). This unique characteristic of the American Dipper has resAmerican Dipper ulted in a number of theories. Some theories suggests that migratory dippers are at an advantage because they are able to minimize any risk of predation to their nest and offspring at higher elevations, which results in more successful reproduction periods and more offspring (Mackas et al. 2010). However, according to two different studies, (Mackas et al. 2010; Middleston et al. 2006) migratory American Dipper individuals that bred at higher elevations ultimately produced offspring in worse condition. Due to these findings, it is said that the migratory dipper offspring are less likely than the residential dipper offspring to survive until the following year (Mackas et al. 2010). That being said, the American Dipper tends to be more sedentary than migratory with around 74% of the population remaining residential according to a more recently conducted study (Middleton et al. 2006). Importantly noted, offspring produced at different elevations has not shown to actually produce better quality offspring (Mackas et al. 2010).

So why does the American Dipper population have some individuals who tend to migrate even though the offspring produced in these migratory areas tend to be in worse condition and there are no offspring quality differences? Further investigation has found that migration has evolved in the American Dipper once all sedentary populations realized there was too high a competition for such limited resources. This resulted in a number of individuals to seek other areas for breeding opportunities located away from their initial range (Gillis et al. 2008).

The American Dipper’s preference for turbulent moving streams and rivers is important for helping to protectAmerican Dipper feeding babies its nest (Montana Outdoors 2003). The male and female dippers come together each spring at the nesting sight to reproduce (Montana outdoors 2003). During the mating season, the male dipper begins the mating “ritual” (Animal Diversity Web 2001). This consists of an intricate performance intended to impress and attract the attention of a female dipper. The ritual begins with the male stretching his neck upward while keeping his wings partially spread and pointed downward. In addition, the male keeps his bill held vertically while flashing his bright white eyelids to show courtship. He then proceeds to sing and strut around in front of the female (Animal Diversity Web 2001). If the female dipper is impressed by the male’s song and dance performance, together the two begin to perform together and they eventually end the mating ritual by touching their breasts together (Animal Diversity Web 2001).

Usually the American Dipper lays two to five white colored eggs, which the female broods for around a 16-day incubation period (Montana Outdoors 2003). Once the baby dippers hatch, they remain in the nest for an average of 24 days. In the meantime, the male dipper helps the female dipper in feeding the baby dippers (Montana Outdoors 2003). After the 24-day period following the offspring hatching, the young offspring are able to leave the nest and swim and dive for their own food (BirdWeb 1999). Typically the females will produce two broods a year.  

                       American Dipper feeding its young

<<Form and Function                                       References                                            Interactions>>