Chapters 1 - U.S. Fish and Wildlife Service

Chapter 4
sand, in which one to four eggs are laid, usually two. At Seal Beach NWR, the first eggs are
generally laid in the second week of May and the last eggs are laid in late June (Collins 2007).
Range-wide, only one brood is raised; however, the birds will re-nest if eggs or chicks are lost.
Parents continue to feed their young even after they are strong fliers
Observations indicated that California least terns lay their eggs at different times generally based
on the age of the birds. The first eggs at a nesting site are generally laid by older birds, with a
second round of egg laying by younger birds (2 to 3 years old) generally initiated by June 15
(Massey and Atwood 1981). Re-nesting by the older birds may also occur in June for those that
lost eggs or young chicks during the initial nesting period. The peak of egg laying at Seal Beach
from 2003 to 2007 was the third and fourth weeks of May and the first week of June (Collins 2007).
This tern species is an exclusive fish-eater, typically feeding on topsmelt, northern anchovy, gobies,
and jacksmelt (Massey 1974, Atwood and Kelly 1984). Studies on fish dropped at nesting sites
suggest that fish size, rather than species, is the essential requirement of suitable prey for the least
tern. Feeding is carried out in the calm waters of narrow estuaries or large bays and for a short
distance (i.e., usually within two miles of the beach) in the open ocean. The hovering and plunging
habits of this species are conspicuous. Adults that are not feeding young tend to go farther and
prey on larger fish. After the eggs have hatched, however, the parents make shorter trips,
bringing back smaller fish for their chicks. This need to locate smaller fish appears to result in the
increased use of freshwater marsh systems and estuarine areas during the post-breeding dispersal
phase, suggesting the importance of such habitats when juveniles are learning to fish.
The California Least Tern Recovery Plan, which was originally approved in 1980 and updated in
1985 (USFWS 1985a), outlines the actions that should be implemented to restore the California
least tern to a stable, non-endangered status. The plan’s primary recovery objective is to restore
and subsequently maintain the breeding population of California least terns at a secure level so
that delisting can be considered. According to the 1985 recovery plan, the annual breeding
population in California must increase to at least 1,200 pairs distributed among secure colonies in
at least 20 coastal management areas throughout their breeding range. In addition, each secure
coastal management area must have a five-year mean reproductive rate of at least 1.0 young
fledged per breeding pair.
According to the results of the five year review for the California least tern prepared by the
Service in 2006 (USFWS 2006), the reproductive rate for the species in 2005 was 0.23 to 0.36
fledglings per pair, which is considerably lower than the values recommended in the Recovery
Plan. Despite this lower reproductive rate, the California least tern population in 2005 was
estimated at approximately 7,100 pairs, nearly six times greater than the number identified in the
Recovery Plan for downlisting and delisting. The Service in the five year review for the least tern
indicated that current population figures suggest that the recovery criterion of no less than one
fledgling per pair may not be necessary for recovery of this species as populations increases
appear to be occurring despite lower reproductive rates. Preliminary estimates of the number of
breeding pairs in California in 2010 range from 6,428 to 6,585 breeding pairs, with an estimated
0.27 to 0.37 fledglings per pair (Dan Marschalek, CDFG, 11/17/10).
At Seal Beach NWR, least terns currently nest on a peninsula referred to as NASA Island, a
three-acre fill site that was converted from military use to a potential least tern nesting site
between 1977 and 1979. Historically, California least terns likely foraged in Anaheim Bay and
nested on the adjacent coastal beaches of Seal Beach and Sunset Beach (Collins 2007). Intensive
human use of these beaches likely caused the birds to seek nesting sites elsewhere along the coast.
In 1969, least terns were found nesting on a fill area in Sunset Aquatic Park and utilized the area
4-60 Seal Beach National Wildlife Refuge