BALD EAGLE NEST MONITORING

INTRODUCTION

Though no historical information exists on Bald Eagle (*Haliaeetus
leucocephalus*) population size in California, it is widely thought that
this species formerly occupied a widespread range and was quite abundant
throughout the western states. After World War II, the Bald Eagle
population declined rapidly in California and throughout all other parts
of its range. This was caused primarily by DDT contamination which
caused severe nesting failure in this species. Another factor
contributing to its decline was degradation of breeding and wintering
habitats. In 1967 the United States Fish and Wildlife Service (USFWS)
listed the Bald Eagle as Federally endangered, followed by the State of
California which listed the species as endangered in 1971. By the late
1960s and early 1970s, fewer than 30 nesting pairs remained in
California, all in the northern part of the state (Jurek, 1990).

Fortunately, the last 30 years have seen a remarkable turnaround in
population numbers and occupied sites for the Bald Eagle. Protection of
nesting areas, restrictions on use of DDT and other pesticides, and
wildlife management projects designed to enhance bald eagle populations
have all played significant roles. By 1994, the number of occupied
territories in California had increased from 30 to 116. Likewise, the
wintering population had stabilized around 1000 birds. Annual
productivity for the species has been considered good during the last
decade, with slightly more than one young being produced per occupied
territory. Partly because much progress has been made toward meeting
most of the population recovery criteria (as specified in the Pacific
Bald Eagle Recovery Plan) (Jurek, 1995), the USFWS recently officially
reclassified the Bald Eagle to threatened.

Lassen Volcanic National Park (LVNP), since 1980, has actively
participated in a multi-agency program of annual breeding season
surveys. This program, which is managed by the California Department of
Fish and Game (CDFG), has provided a relatively thorough statewide
coverage of the status of breeding Bald Eagles.

PROJECT HISTORY

The current Bald Eagle monitoring effort has been in place for more than
20 years and stems from written management recommendations provided by a
1980 study of endangered raptors in the park (Baldridge et al., 1980).
The purpose of that study was to document the distribution of endangered
raptors (Bald Eagle and Peregrine Falcon) in LVNP, determine if these
species nested in the park, and implement a monitoring system for these
federally-listed species which could be continued by park personnel.
Significant findings of Baldridge's study were: 1) discovery of the
first active Bald Eagle nest in the park, at Snag Lake, 2) the Snag Lake
nest is probably the highest in elevation of any in the state, and 3)
LVNP has extremely marginal Bald Eagle nesting habitat because of scarce
food supplies and relatively harsh climates during the nesting season.
Therefore the park can support at most one resident breeding pair, in
addition to one other foraging pair which nests outside the park, and a
few wandering juveniles.

The nest that was used in 2000 blew down during the winter or spring of
2001. No new nest has been located since 2000. Adult Bald Eagles have
been observed in the Butte Lake, Snag Lake, and Cluster Lakes areas
since 2000.

METHODS

Two observation posts are used to make on-ground surveys of the nest
tree during the breeding/fledging season. The principal post is located
one half mile west/northwest of the nest, and the secondary post is
located east/northeast near the southwest edge of Snag Lake. Observation
posts and nest trees have been mapped using a GPS device. Observations
generally occur approximately once per week from early June until young
Bald Eagles fledge (sometimes as late as early August), or until it is
determined that no young are present. Observations are taken using a
20-45 power spotting scope and binoculars. In addition to time spent at
the observation posts, observations are made of the entire Snag Lake
region from trails along the lakeshore and prominent points affording
adequate views of the lake. In years of nesting success, detailed
records are kept of adult foraging behavior, foods obtained, adult and
nestling interactions, and alternate nest building and nest repairing
activities. Data are recorded on standard CDFG eagle monitoring forms
and submitted to State offices in Sacramento.

RESULTS

Due to late snowfall Snag Lake was not officially surveyed in 2006. The
crew conducting California Spotted Owl surveys looked for Bald Eagles as
they traveled by Snag Lake in late July and August, but did not observe
any Bald Eagles. There were no Bald Eagle sightings from park staff or
visitors at Snag Lake in 2006.

There were two sightings of Bald Eagle adults at Manzanita Lake in 2006.
On April 28^th^, one adult and one juvenile were flying around the lake.
On July 11^th^, a single adult was seen flying around the lake.

Bald Eagle nesting success at the Snag Lake site has occurred in eleven
of the 28 years of nest monitoring (Table 1).

FUTURE DIRECTION

Nest site monitoring will continue indefinitely at the Snag Lake nest
site. Additional nesting sites located within the park will be monitored
using established protocol.

**Table 2. Snag Lake Bald Eagle nest history, Lassen Volcanic National
Park.**

[Year Hatched, (Fledged) Mode of Survey Comment]{.underline}

1979 unk., (1) Foot No nest located

1980 No Aircraft, foot 1 nest located

1981 No Aircraft No nest located

1982 No Foot No nest located, late thaw

1983 2, (1) Foot 1 nest located, late thaw

1984 2, (1) Foot Same tree as previous year

1985 ? \-\-- Not Surveyed

1986 ?, (1) Foot 2 nests located, 1 nest destroyed by end of yr

1987 2, (1) Foot Alternate nest rebuilt, then collapsed;

eaglet remains collected; snag fire Aug-Sept

1988 No Foot Evidence of spring nest-building attempts

1989 No Foot Nest used in '83 and '84 fully intact

1990 No Foot No evidence of nesting or territorial behavior

1991 No Foot No evidence of nesting or territorial behavior

1992 1, (1) Foot Same nest as used in '83 and '84

1993 1, (1) Foot Same nest as used in '83 and '84

1994 ? \-- Not Surveyed

1995 No Foot Heavy winter snow, late thaw

1996 1, (1) Foot

1997 1, (1) Foot

1998 No Foot El Nino winter; evidence of spring nest-building

1999 1,(1) Foot Probably same nest as used in 1995

2000 1,(1) Foot Same nest as used in 1999

2001 No Foot No nest located

# 2002 Unk Foot No nest located 

# 2003 Unk Foot One nest located (historic nest) 

2004 Unk Foot One nest located (historic nest) no activity

2005 Unk Foot One nest located (Historic nest) no activity

[2006 Unk Foot Status unknown]{.underline}

#