Post-ovulatory follicles (POFs) are often used to estimate egg production of collected birds, especially in studies of nutrient-reserve dynamics of laying waterfowl. We assessed the reliability of this technique in American Coots (Fulica americana) by conducting macroscopic and microscopic POF counts and comparing these estimates with egg counts obtained through frequent nest monitoring. Macroscopic POF counts were unreliable, but microscopic counts were significantly correlated with known clutch size (r = 0.74, n = 12, P = 0.006). On average, microscopic POF counts differed from known clutch size by -0.42 (SD = 1.51), which represented approximately -4% bias and 15% measurement error. Errors in POF counts were likely due to rapid regression of POFs or to mis-identification of atretic follicles. We used simulation modeling to assess the effects of such errors on estimates of nutrient commitment to clutch formation. Our simulations showed that small errors in POF counts are unlikely to have any serious effects; investigators concerned with low power and precision could benefit most by obtaining adequate sample sizes.
|Translated title of the contribution||Using post-ovulatory follicles to determine laying histories of American Coots: Implications for nutrient-reserve studies|
|Number of pages||7|
|Journal||Journal of Field Ornithology|
|State||Published - 1997|