After more than a decade of research, we have been able to rule out many probable causes of beak deformities in Alaskan birds. Recently, we used next generation sequencing (NGS) to investigate the hypothesis that a virus might be responsible for avian keratin disease (AKD). NGS is a powerful tool for studying new and emerging diseases because it can provide information about viruses and other pathogens that have not previously been described. 

In 2016 we detected a novel picornavirus (Poecivirus) in beak tissues of Black-capped Chickadees with AKD (Zylberberg et al. 2016). We detected this virus in 100% of birds with beak deformities; by comparison, the virus was present in only 20% of birds with apparently normal beaks. Subsequently, we sampled a larger number of chickadees from our field sites in south-central Alaska and confirmed a strong association between Poecivirus and beak deformities. 

Additionally, we have detected a closely related virus in other species from Alaska with beak deformities, providing further evidence for Poecivirus as a leading candidate cause of AKD. Other picornaviruses have been associated with keratin overgrowth, such as Seneca Valley virus in pigs (Vanucci et al. 2015). 

However, because Poecivirus is a newly discovered virus, we still have a lot to learn. Additional studies are currently underway to determine if this virus causes beak deformities in naïve birds, whether it is present outside of Alaska, and how it may be transmitted among wild birds.

Previous studies have documented associations between beak abnormalities and nutritional disorders in other species, but we have no direct evidence that nutritional deficiencies are responsible for Alaskan deformities.

Overgrowth of the beak can be caused by nutritional deficiencies of vitamin A, vitamin D3, or calcium, or by an imbalanced ratio of calcium and phosphorus (Altman 1986; Harrison and Harrison 1986). Vitamin D3, which is the form of vitamin D used by birds and is necessary for calcium regulation, is derived from sunlight and either absorbed through the skin or ingested through preening. During short winter days, it is possible that birds may not get adequate sources of vitamin D3 from sunlight. They could also develop nutritional deficiencies from incomplete diets, particularly if they are overly reliant on sunflower seeds at feeders or other human sources of food that are low in calcium and vitamin A and high in fat, which can interfere with calcium absorption. However, observed clinical signs in affected chickadees differ from those previously described for vitamin A, vitamin D3, or calcium imbalances, making these possibilities less likely.

We performed diet analysis with stable isotope analysis of blood and feathers in affected and unaffected chickadees to determine whether beak deformities were associated with differences in diet. While we found that affected birds consumed more foods from human-provided feeders, our results suggested that this difference was likely a consequence rather than a cause of the beak deformities. Because of physical limitations imposed by an elongated beak, affected birds have a difficult time foraging in the wild. Feeders provide more easily accessible food sources.

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 parents with beak deformities are more likely to have deformities themselves than offspring from parents with normal beaks.

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, unpublished report).  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.