Survival of Herring Gull and Domestic Chicken Embryos after Simulated Flooding

Abstract

-The eggs of Herring Gulls (Larus argentatus) and several other marsh nesting species undergo periodic flooding. We conducted an experiment to test the effects of simulated tidal flooding on Herring Gull and domestic chicken (Gallus gallus) eggs. Experimental variables were salinity, temperature, length of immersion, and state of incubation when immersion occurred. In general, Herring Gull eggs had a higher hatching success after immersion and at lower temperatures than did chicken embryos. Herring Gull embryos equally survived immersion during the first and third week of development, whereas more chicken embryos survived immersion during the first week. There were no significant differences between species with respect to the duration of the immersion. Herring Gulls (Larus argentatus) have recently begun breeding in salt marshes of New Jersey that are subject to tidal flooding (Burger 1977), and presently most of their colonies are located on coastal salt marshes or salt marsh islands (Kane and Farrar 1977). Herring Gulls prefer to nest under Iva bushes on the higher parts of the islands, but in the last few years many gulls have nested in lower Spartina alterniflora areas that are subject to tidal flooding (Burger 1977, Burger and Shisler, unpubl.). Immersion of eggs during tidal flooding in the breeding season may result in the death of embryos, but the eggs of bird species that are normally subject to inundation may be more resistant to harmful effects of flooding. For example, many species of ducks have eggs with water-repellent surfaces (Welty 1975), which probably help resist the entry of water. Inundation of Clapper Rail (Rallus longirostris) nests by high tides has no apparent effect on hatching success (Mangold 1974). In New Jersey, Laughing Gulls (Larus atricilla) normally nest in salt marshes that are subject to saltwater flooding (Bent 1921, Bongiorno 1970) and Burger (1979) found that Laughing Gull eggs have a 63% hatching success even after being immersed in salt water for two hours during the third week of incubation. In order to determine effects of flooding on survival of embryos, we immersed Herring Gull and domestic chicken (Gallus gallus) eggs and varied four factors that we thought might be related to death of embryos. The factors studied were salinity and temperature of the water, duration of immersion, and stage of incubation. MATERIALS AND METHODS Field research was conducted on Clam Island, a salt marsh island in Barnegat Bay, New Jersey (39045'N, 74'08'E). The vegetation of Clam Island is primarily Spartina alterniflora and S. patens grass with scattered Iva frutescens and Baccharis halimifolia bushes. The island is divided into four sub-islands, three of which contained 1,200 pairs of nesting Herring Gulls during this study. The majority of the Herring Gulls nested in the higher bush areas of the island. Two hundred pairs of Laughing Gulls nested on the fourth sub-island. The island was checked for nests and eggs one to three times per week from 16 April until 15 May 1978, when it was checked every other day until 10 July. New nests were marked with flags and numbered with metal tags; eggs were numbered with a black felt-tip marker when first discovered. Nests and contents were checked until 10 July, when the fate of all eggs could be determined. When clutches were at the right stage of incubation we collected eggs and randomly assigned one of eight treatments for that stage of incubation to the group of eggs. Eggs removed from a nest for treatment were replaced with an egg from another nest so that the parents would continue to incubate and not vacate the nest. We marked the eggs removed for treatment with a black felt-tip marker so that they could be returned to their original nest. All of the eggs were taken from nests which initially had three-egg clutches, and 89% of the nests had three eggs when treated. We treated only eggs from nests whose date of clutch completion with three eggs was known and we considered the time of clutch completion to be the beginning of the first week of incubation. Eggs within the same nest always received the same treatment and were treated only once. We treated eggs by immersing them completely for the prescribed time in a bucket of water of the chosen salinity and temperature. The levels of the four factors that we used for immersion treatments were as follows: for salinity, ocean water taken from Barnegat Bay and fresh water; for water temperature, 7-90C and 26-280C; for duration of immersion, half an hour and two hours; and for stage of incubation, the first and third weeks of incubation.