Dabbling Duck Eggs Hatch After Nest Abandonment in the Wild

In most birds, parental incubation of eggs is necessary for embryo development and survival. Using a combination of weekly nest visits, temperature dataloggers, infrared video cameras, and GPS tracking of hens, we documented several instances of duck eggs hatching after being abandoned by the incubating female. Of 2826 Mallard (Anas platyrhynchos) and Gadwall (Mareca strepera) nests monitored 2015-2019 in Suisun Marsh, California, 48 (1.7%) were abandoned during late incubation (>= 20 days). Of these, we identified six (12.5%) where at least one egg hatched 2-9 days after abandonment. In all six cases, eggshell membranes were found in the nest (indicating hatch), and ducklings were observed at three nests. Abandoned nests were unattended for an average of 5.9 days before eggs hatched; during this time, mean nest temperatures (23.6 degrees C-29.0 degrees C) were substantially lower than before nest abandonment (31.7 degrees C-36.4 degrees C). We estimated that abandonment resulted in a 9% longer time period between clutch completion and hatch (0-4 days longer) and a lower rate of egg hatching success (36%). Our results provide evidence that some older embryos (>= 20 days) in mild climates can survive without parental incubation for several days and continue to develop (at a reduced rate) to the point of successfully hatching. Received 20 Apr 2021, accepted 31 May 2022.