Effects of low incubation temperatures during the pipped egg stage on hatchability and hatching times in domestic chickens and ring-billed gulls

Gulls and some other species of birds are known to neglect pipped eggs that remain within the clutch after the first egg(s) hatch. I examined the effects of incubation neglect at this stage of development by cooling eggs in the laboratory. Domestic white leghorn chicken (Gallus gallus) eggs had significantly reduced hatchability and delayed hatch times when incubated at 30 or 27 °C from pipping until hatching. Cyclic cooling for 4 or 7 h out of every 8-h period produced intermediate effects. Pip-to-hatch interval was delayed by as much as 60% in ring-billed gull (Larus delawarensis) eggs incubated from pipping onwards at 33 °C. To the extent that the laboratory results can be extrapolated to natural incubation, results suggest that egg neglect and low incubation temperatures during the critical final stages of hatching could have adverse effects upon the last egg(s) to hatch within a clutch. Depending on the species, low temperature and retardation could increase chances that a late-hatched young will be left behind when the rest of the brood leaves the nest. Where the hatch is typically asychronous, low incubation temperatures after the first eggs begin to hatch could increase the degree of asynchrony and hence the competitive disadvantage of the last-hatched young.