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Genetics

Black-capped Chickadee with curved upper mandible - photo by don Kuhle
Black-capped Chickadee - photo by Don Kuhle

We sampled blood from all captured Black-capped Chickadees to determine sex of the birds, identify family relationships, and assess potential DNA damage.

We found no evidence to suggest that beak deformities among Black-capped Chickadees are heritable in nature.  However, the fact that deformities appeared in adult birds and not nestlings made it difficult to establish this conclusively.  Because we only recapture a small proportion of the adults in a population, we have a limited sample size of birds from known parents.  Additional analysis of genetic data will help determine if offspring from deformed parents are more likely to be deformed than offspring from normal parents. 

In addition, genetic paternity analysis identified surprisingly high rates of “cheating” among pairs.  In many cases, the female, the male, or both adults mated with a different bird whose eggs subsequently ended up in the pair’s nest.  Occasionally, eggs from two completely different adults were “dumped” in a pair’s nest as well.  These complicating factors make genetic analysis especially important when examining effects across generations or relationships between the eggs or chicks in a nest.  Contaminant concentrations, for example, are often compared between siblings or between a female and her eggs.  Due to high rates of “cheating,” these relationships cannot be accurately determined without genetic fingerprinting of individuals.

We also tested for DNA damage in Black-capped Chickadees with a technique called flow cytometry.  Results from these tests indicated that chickadees with beak deformities had a significantly greater amount of DNA damage than normal chickadees (Easton 1999).  Such damage to the DNA can result from exposure to contaminants (Custer et al. 1994) or some other specific mutagen, such as a disease organism.

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