Frustrating morning at Concord Park

I arrived at Concord Park this morning around 8:20. It was 70, overcast, with mild winds. My target birds were Brown-headed Nuthatch and Great Crested Flycatcher; I found neither, though both are usually there, I'm told. I did find two Starling nests and a host of grown Starlings; one Chipping Sparrow; 10 or so American Goldfinches; crows, robins, lots of Mallards (adult, juvenile, and immature), about 50 Canada Geese; some Muscovy hybrids and Greylag Geese; Carolina Wren (heard only); Carolina Chickadees (heard); 4 Great Blue Herons; and a Red-bellied Woodpecker heard singing from the island. It was a frustrating day because most of the passerines I could only hear; I couldn't find them in my bins. I'm going to try again on Thursday.