Effects of Variable Humidity on Embryonic Development and Hatching Success of Mourning Doves

Newly laid Mourning Dove (Zenaida macroura) eggs were held at a constant temperature of 37.5øC at one of three relative humidities: 0-5% ("arid"); 35-45% ("interme-diate"); and 95-100% ("humid"). Samples in the humid treatment lost significantly less water than those in intermediate or arid treatments. There was significantly more water in embryos of the humid treatment than in the intermediate or arid treatments. Protein and carbohydrate content of samples in the humid treatment was significantly smaller than those in inter¬mediate or arid treatments, whereas lipid and ash contents did not differ among the three treatments. Even in the worst case of constant exposure to near-saturation humidities, 50% of embryos succeeded to hatching. This is, however, significantly below the 85% or 90% hatching success characteristic of the arid or intermediate humidities, respectively. Of the doves that failed to hatch in the humid condition, 90% developed to pipping and initiated aerial respiration. Contrary to previous analyses that suggested that hatching failure is likely due to the embryo's failure to initiate pulmonary respiration or to maintain constant hydra-tion, the failure of Mourning Dove embryos to hatch apparently was due to severe mechanical restriction upon movement within the rigid shell. This was produced by the lack of adequate internal space produced by evaporative water loss.