Effects of Beak Deformities on Birds

Physical limitations associated with beak deformities can change normal behavior patterns. 

• Affected birds are often seen picking up food with their heads turned sideways because an overgrown or crossed beak prevents them from eating normally.
• Birds with deformities may also change their foraging habits to include more easily acquired foods.
• Severe deformities make it difficult for birds to forage and they may instead rely heavily on feeders and other sources of supplemental food.
• Affected chickadees, nuthatches, and woodpeckers with beak deformities often feed on the snow beneath feeders, picking up scraps dropped by other birds.
• Affected crows, ravens, magpies, and jays are frequently seen outside of grocery stores or fast-food restaurants or near city dumps.

In addition to changes in foraging behavior, some birds with beak deformities also exhibit abnormal behavior during breeding. 

• We documented several cases in which a female parent with a beak deformity abandoned the nest after she was banded
• Most unaffected females tolerated such disturbance quite well and returned to incubate eggs immediately after they were released.
• In other cases, females with beak deformities behaved erratically, and eggs were scattered about the nest box haphazardly rather than arranged neatly in a nest cup.
• It is still unclear whether this behavior results from a physical limitation imposed by the bill deformity or from hormonal or physiological disruption of incubation behavior.
• Analysis of nest box video data will help us learn more about the causes of abnormal behavior among chickadees with avian keratin disorder (AKD).

Although many Black-capped Chickadees in the south-central Alaskan population successfully raise 6-8 young each year, parents with beak deformities face greater challenges. In our 2000-2004 breeding study, 305 nest boxes were used by Black-capped Chickadees. Of these, 33 were occupied by pairs in which either the male or the female had a beak deformity. In one unusual case, both the male and the female from a nest were affected.

For nests in which the female had a beak deformity, fewer eggs hatched on average. This may have been due to a physical problem with the eggs, such as thinner eggshells, or a behavioral change, such as reduced incubation by the female.

For nests in which the male had a beak deformity, a smaller proportion of the young survived to leave the nest. 

• It is likely that the physical deformity hindered the male’s ability to gather enough food for the nestlings. 
• In addition, we were surprised to find that affected males had to cope with a different problem—being tricked into raising someone else’s young. 
• Genetic studies showed that nests used by an affected male contained a higher proportion of eggs from a different male or from different parents entirely. 
• Although the reason for this pattern is not known, we suspect that affected males were less able to defend their territories due to difficulty foraging, which resulted in long periods away from the nest.

Despite these problems, a surprising number of chickadees with beak deformities do appear to find mates and breed.