These temporal shifts from a marine to terrestrial prey highlight the resilience adult gulls have and their ability to keep chick condition consistent.
The gulls relied substantially on the Henslow's swimming crab (Polybius henslowii). Yet, in times when local prey availability is low, the gulls shift to human-related food.
Analyzing both adult and chick remains, researchers found a mixture of both natural prey and human refuse.
Between the years of 1974–1994, yellow-legged gull populations in Berlenga Island, Portugal, increased from 2600 to 44,698 individuals.
Lastly, closure of nearby open-air landfills limited food availability for the gulls, furthering creating a stress on their shift in diet.
This shift was linked to higher fishing efficiency and thus overall fish stock depletion.
Analysis of yellow-legged gull's (Larus michahellis) pellets off the northwest coast of Spain revealed a shift from a sardine to crustacean-based diet.
Looking at the effect of humans on gull diet, overfishing of target prey such as sardines have caused a shift in diet and behavior.
Examples of such associations include four species of gulls feeding around plumes of mud brought to the surface by feeding grey whales,and also between orcas (largest dolphin species) and kelp gulls (and other seabirds).
To obtain prey from deeper down, many species of gulls feed in association with other animals, where marine hunters drive prey to the surface when hunting.
