Anatomical and morphometrical comparison of the crop between brooding and non-brooding Java sparrow

Background: In certain bird species, such as the Java sparrow, the crop plays a role in parental care, particularly in the production of crop milk to feed the offspring. Despite its importance, limited studies have focused on it. Thus, the crops of 12 Java birds were used in this study and divided into brooding and non-brooding groups to highlight the differences between them and to document the morphometrical adaptations associated with brooding behavior.Aims: This study aimed to precisely identify and characterize the distinct anatomical differences in the crop of Java sparrows (e.g., location, shape and dimensions of the brood patch as well as to assess the morphological changes that occur between brooding and non-brooding periods). Results: The crop is located at the center of esophagus as simple fusiform or spindle-shaped. Its outer surface was thick and encircled by skin and adipose tissue in the brooding birds, in contrast to only skin of the non-brooding. In brooding birds, the inner surface of the crop contains circular and longitudinal folds, whereas in non-brooding only longitudinal folds in both sexes were observed. Moreover, in brooding birds, the weight and dimensions of the crop were varied and appeared longer and wider than non- brooding species in both sexes. Conclusions: The observed variations highlight the functional adaptation of the crop to meet the physiological needs of parental care, providing valuable insights into avian reproductive anatomy.