Current Research

| Northwestern Crows | Diet Analysis | Histopathology | Captive Study |

Northwestern Crows

We began research on Northwestern Crows in spring of 2007 and have since captured approximately 180 birds at six locations throughout Alaska: Seward, Kenai, Homer, Valdez, Haines, and Juneau (Figures 27–29).  Captured birds were measured, examined for beak and other keratin abnormalities, and banded with a USGS metal band and a unique combination of three color bands (Figures 30–31).  These markings will allow us to track individuals’ movements and changes in beak growth over time.  If you see banded and/or deformed crows in your community, please be sure to report them here. Affected crows were present all locations sampled during the 2006–07 and 2007–08 winter seasons (Figures 32–34).  Based on results from this study, we estimate prevalence of deformities among Northwestern Crows in Alaska to be 16.9% (±5.3%), the highest rate of gross deformity ever documented in a wild bird population!

Figure 27.  Northwestern Crow trap in Seward, Alaska.  Photo by Charlie Finn

Figure 28.  Northwestern Crow trap in Haines, Alaska.  Photo by Patrick Farrell.

Figure 29.  Removing crow from trap.  USGS photo.

Figure 30.  Northwestern Crow with metal and color bands, Haines.  Photo by Judy Heinmiller.

Figure 31.  Northwestern Crow with metal and color bands, Juneau.  Photo by Gus van Vliet.

Figure 32. Deformed crow, Juneau, Alaska. USGS photo.

Figure 33.  Deformed crow, Seward, Alaska.  USGS photo.

Figure 34.  Deformed crow, Juneau, Alaska.  USGS photo.

Stable Isotope Diet Analysis

Analysis of diet via stable isotope analysis of blood and feathers in normal and deformed crows and chickadees will help determine whether beak malformations are associated with differences in diet.  Preliminary analyses of δ13C and δ15N ratios in chickadee blood suggested that affected birds may consume more foods from human-provided feeders and less natural insect and animal matter than normal birds (C. Van Hemert, unpublished data).  If deformities are associated with nutritional problems or environmental contaminants, diet is the most likely route of exposure.  Therefore, determining dietary differences may have important implications for assessing potential causes of beak deformities.  We will also use stable isotope analysis of captive birds with known diets to refine the interpretation of data from free-ranging individuals. 

Histopathology of Beaks

Additional pathology work will provide clues about mechanisms and potential causes of abnormal beak growth and will help direct future research efforts. An intensive histological assessment of normal and affected birds is currently underway to characterize this disease and identify cellular abnormalities associated with deformities. Preliminary results provide evidence of hyperkeratosis and abnormal maturation of keratin cells. Histological examination of other keratinized structures, including claws, feathers, and skin, suggests that this may be a systemic disorder affecting multiple tissues. We are also employing additional diagnostic techiques, including scanning and transmission electron microscopy, to detect pathological changes in affected birds.

Figure 35.  Tip of maxilla from severely deformed Black-capped Chickadee mid-sagittal section.  Stained with hematoxylin and eosin; 50x magnification.  USGS photo.

Captive Black-capped Chickadees

We recently conducted a captive study of beak growth in Black-capped Chickadees. Basic understanding of the growth processes involved in production of beak keratin is critical for understanding possible mechanisms that may be leading to deformities. However, no previous studies have confirmed either the rate or pattern of beak growth in any passerine species.

Preliminary results from this study indicate that rapid proliferation of keratin is primarily responsible for gross beak deformities. Affected birds exhibited faster rates of beak keratin growth, sometimes exceeding normal growth rates by more than two times. We also documented high, unexplained mortality rates and elevated incidence of skin lesions in birds with beak deformities.