Current Research

| Northwestern Crows | Diet Analysis | Remote Sampling | 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). 

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.

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.

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.

We captured deformed crows at most locations sampled during the 2006–07 and 2007–08 winter seasons (Figures 32–34).  Based on preliminary results from trapping efforts, prevalence of deformities among Northwestern Crows in Alaska appears to be higher than normal background levels.

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 deformed birds have enriched δ13C signatures, indicating that deformed birds may consume more foods from human-provided feeders than normal birds (C. Van Hemert, unpublished data).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. 

Prevalence of Deformities in Remote Areas

No information currently exists about the possible occurrence of deformities in unpopulated areas and an important question remaining to be addressed is whether an association exists between bill deformities and human populations.  Surveying birds in remote areas will allow us to test for such an association and may provide clues about possible causes.  Preliminary results from trapping efforts of Black-capped Chickadees on the Kenai National Wildlife Refuge suggest that deformities do occur away from human communities.

Histopathology of Beaks

More pathology work will help provide additional clues about the potential causes of abnormal beak growth and may help direct our future efforts.  The physiological and histological changes associated with deformities have been poorly described, in part due to limited knowledge of the mechanisms involved in beak keratin growth.  Very few sources that address histology of avian beaks currently exist in the literature.  An ongoing intensive histological assessment of normal and deformed birds will help characterize this disease and identify cellular or tissular abnormalities associated with deformities.

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

Captive work in controlled conditions will allow us to determine rates and patterns of beak growth and potential causes of overgrowth 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.
We suspect that rapid proliferation of keratin may be leading to gross beak deformities, but no quantitative data currently exist to describe physiological differences associated with deformities.  By employing a combination of external measurements, radiography, and dietary markers, we will better understand physiological changes associated with deformities which will help identify potential mechanisms responsible for inducing overgrowth of affected beaks.