Seasons of Wildlife

Nature's Calendar at the San Luis NWR Complex


  • Numbers peak for geese and ducks
  • Bald eagles often observed perched and hunting where migratory birds are concentrated at feeding and nesting areas
  • Winter sees greatest diversity of raptors


  • Great horned owls hatching
  • Hawks exhibiting aerial courtship displays
  • Large numbers of wintering waterfowl and cranes visible


  • Waterfowl begin migrating north
  • Hawks and herons begin nesting
  • Shorebird numbers building
  • Snakes encountered basking in the sun
  • Beckwith wildlife observation area at San Joaquin River NWR closes for the season as geese and cranes migrate north


  • Wildflowers in bloom
  • Seasonal wetlands are drained to allow waterbird food plants to grow
  • Peak number of shorebirds
  • Summer neotroprical songbirds begin arriving


  • Peak nesting time for hawks and herons, and early nest fledging begins
  • Shorebirds are migrating in breeding plumage
  • Songbirds are very vocal defending nesting territories
  • Tiger salamanders return to burrows as vernal pools dry


  • Shorebirds migrate north
  • Seasonal wetlands are dry
  • Songbird, heron, and raptor fledglings are visible


  • Seasonal wetlands are irrigated to encourage waterbird food plants to thrive
  • Fall shorebird migration begins
  • Coyote pups out exploring their territories


  • Swainson's hawks have fledged and will form "kettles" over grasslands
  • Irrigated pastures attract ibis and long-billed curlews
  • Some early northern pintails arrive


  • Sandhill cranes begin returning mid-month
  • Aleutian cackling geese begin returning end of the month
  • Greater white-fronted geese begin arriving
  • Songbirds migrate south
  • Monarch butterfly fall migration peaks
  • Black-tailed deer rut begins


  • Aleutian cackling goose numbers increasing at San Joaquin River NWR
  • Beckwith wildlife observation area at San Joaquin River NWR opens for the season
  • Greatest bird diversity occurs during fall and spring migrations
  • Juvenile snakes emerge


  • Wetlands fully flooded
  • Sandhill cranes are abundant
  • Ross’ geese arrive
  • Tiger salamanders begin trek to vernal pools to breed
  • Large numbers of ducks present


  • Snow geese begin to arrive at San Joaquin River NWR
  • Swans may arrive in small numbers
  • Watch for eagles, falcons, and ferruginous hawks

Featured Species

Aleutian Cackling Geese

A flock of Aleutian cackling geese in a wetland at the San Joaquin River NWR.

Each fall, Aleutian cackling geese migrate from their breeding grounds in Alaska’s Aleutian Islands to California’s northern San Joaquin Valley. Through the winter, nearly all the Aleutian cackling geese in the world can be found on the San Joaquin River NWR and neighboring private lands. These geese arrive in October and November and begin to return to their breeding grounds in March.

The geese once nested in large numbers on the Aleutian Islands; however, by 1975 their total population had declined to fewer than 800 birds. Their wintering habitat in the San Joaquin Valley was shrinking, and introduced arctic foxes in their Alaskan breeding grounds were eating their eggs and young. The geese were placed under the protection of the Endangered Species Act. In 1976, most of the remaining 800 geese were found wintering on lands near Modesto, California in the northern San Joaquin Valley. These lands were established as the San Joaquin River NWR to protect wintering feeding and resting areas for the geese. At the same time, the arctic foxes were removed from the geese’ nesting islands in Alaska. These successful efforts resulted in the Aleutian cackling goose being removed from the endangered species list in 2001 and achieving a population of over 200,000 birds today.

Riparian Brush Rabbit

Riparian brush rabbits once thrived in the riparian riparian
Definition of riparian habitat or riparian areas.

Learn more about riparian
woodlands of California’s Central Valley, but their numbers dwindled to near-extinction because of habitat loss. Since 2002, the Fish and Wildlife Service and conservation partners have worked to restore thousands of acres of riparian woodlands and to re-establish populations of riparian brush rabbits at the San Joaquin River NWR. About 1,000 captive-bred rabbits have been released in the refuge’s dense riparian woodlands. The program has been highly successful with native-born rabbits now found throughout the riparian habitat on the refuge and nearby areas.