PROCESSES FEEDING CHICKS CONTEXT Many birds make their reproduc- tive “decisions” about how many eggs to put in the nest, and therefore how many hungry chicks they will have to feed, based on the abundance of food early in the breeding season. Cormo- rants forage in the open waters of the Estuary, reflecting the condition of the pelagic food web influenced by the ocean. Wading birds like her- ons and egrets, by contrast, reflect the condition of more shallow water and wetland food webs around the edges of the Estuary. The reproductive success of Brandt’s cormorants provides a reliable index of prey availability for foraging seabirds in the San Francisco Bay. These fish-eating birds are at the top of the marine food chain. The ability of parent birds to adequately feed their chicks is a good measure of food supply. Their success at rearing chicks is also a re- quirement for healthy, self-sustaining populations. The brood size of great egrets and great blue her- ons also reflects the supply or availability of prey to feed nestlings. Favoring the edges of water, the success of these species in raising young can also be sensitive to changes in the extent and quality of foraging habitat (land-use, water circulation and depth, geomorphology, environmental contam- ination, and vegetation characteristics). The two species targeted for this indicator feed in different habitats: great egrets prefer small ponds in emer- gent wetlands and areas with shallow, fluctuating water depths. In contrast, great blue herons forage along the edges of larger bodies of water and creeks and are less sensitive to water depth. Previous work in the Estuary demonstrated that pre-fledging brood size in local egrets and herons is influenced by the extent of wetland habitat types as far as 10 kilometers (km) from nest sites. Thus, this indicator reflects wetland condition and ecological health over large landscapes. INDICATORS For Brandt’s cormorants, the indicator is the number of fledged young produced per breeding pair at the breeding colony on Alcatraz Island, in San Francisco Bay. (Fledging refers to surviving long enough to leave the nest). The indicator has been studied on Alcatraz Island since 1995. A comparable time series has been collected on the Farallon Islands since 1972. The specific calculation used is the mean for the most recent three years. The benchmark is the number required to maintain a stable population, estimated at 1.5 cormorant chicks fledged per year per breeding pair. For egrets and herons, the indicator is the number of young produced per successful nest. Successful nests are those from which at least one chick reaches the age of fledging. Nest success is evaluated at the critical time just prior to fledging when great blue heron nestlings are 5-8 weeks old and great egrets 5-7 weeks old. Scientists calculated this indicator as the mean prefledging brood size at 40-50 colony sites within foraging range (10 km) of the historic tidal wetland boundary. Brood size was averaged annually (1991-2014) among nests within and across the three major subregions of northern San Francisco Bay (Central San Francisco Bay, North Bay, and Suisun Bay). The benchmark is REARING YOUNG CORMORANT CHICKS REARED CENTRAL & N O R T H B AY S . . S TAT U S . . Good . . . .T R E N D . . . . Stable with long-term gradual decline .....BENCHMARK..... Number required for a stable population Photo: Rick Lewis HERON AND EGRET CHICKS REARED SAN FRANCISCO AND S U I S U N B AY S . . S TAT U S . . Fair . . . .T R E N D . . . . Mixed .....BENCHMARK..... Number of young 1991-2000 73