While collecting my data, I have observed that the number of gulls (Larus spp.) present on the beach is much greater at low tide. I have also observed that there are more gulls on the beach when the low tide occurs in the late afternoon and early evening as opposed to in the morning. These observations are true only for one of the three zones of the beach where I collected my data. Gulls were numerous mainly in the rocky intertidal middle zone, in contrast to the two sandy zones of the beach. I have also observed that the number of birds of other genus or species does not seem to vary in function of tides.
The main ecological process underlying the presence of gulls in a rocky intertidal zone at low tide is foraging. Gulls are known to forage for invertebrates in rocky intertidal zones. Their main preys are mussels, chitons, limpets, urchins, sea stars, sea cucumbers, crabs and barnacles. They also prey on small fishes in the shallow water adjacent to the intertidal zone. Gulls are often seen foraging within one hour of the lowest tide since a greater area of the intertidal zone is exposed at that time. Gulls are also known to display other behaviors while in the rocky intertidal zone, such as resting. Some of the others birds that I have observed while conducting my study are buffleheads, common merganser, eagle and common goldeneye. These birds are known to dive in order to forage for their food (invertebrates and fishes). This foraging behavior explains the reason why these birds were not seen in higher number foraging in the rocky intertidal zone at low tide.
Another aspect of my study is the presence of the creek that flows into the ocean right over the rocky intertidal zone. I have been trying to find a link between the presence of the creek and that of a rocky intertidal zone. I would like to find out if the creek is responsible for the presence of the rocky zone. I have also been trying to determine if the creek influences the presence of preys in the intertidal zone through an increase in the amount of nutrients available. I am still searching answers to these questions.
The three key words that I could use to describe my research project are gulls’ (Larus spp.) foraging behaviors, rocky intertidal zone and invertebrate predators.
ok good!