Bufflehead x Common Goldeneye Hybrid Winters for over a Decade in the Sacramento Region, California

Abstract

An adult male Bufflehead (Bucephala albeola) x Common Goldeneye
(B. clangula) hybrid was observed annually in winter in the Sacramento,
California, region from 2014 through 2024, a noteworthy record of
longevity. The bird was seen annually, with most observations within a
2-km segment of the American River. During two winters over 2022–2024,
it was also seen intermittently on a nearby pond in West Sacramento. The
hybrid showed intermediate characteristics of both possible parents in
size and plumage, and it associated almost exclusively with Common
Goldeneyes, as is typical for this hybrid type. The lifespan of this hybrid is
unusually long compared to either parent species.

Full text

Volume 27 Number 2 51
Buehead x Common Goldeneye Hybrid Winters for
over a Decade in the Sacramento Region, California
Daniel A. Airola1, Frank Severson2, Andrea Willey3, Chris Conard4,
and Jeri M. Langham5
1Conservaon Research and Planning, Sacramento, CA.
d.airola@sbcglobal.net
2 West Sacramento, CA. frankseverson@gmail.com
3Waterbird Habitat Project, Sacramento, CA. andrea.willey@mac.com
4 Rio Bravo Circle, Sacramento, CA. conardc@gmail.com
5Mira Del Rio Drive, Sacramento, CA. jerilangham@icloud.com
ABSTRACT
An adult male Buehead (Bucephala albeola) x Common Goldeneye
(B. clangula) hybrid was observed annually in winter in the Sacramento,
California, region from 2014 through 2024, a noteworthy record of
longevity. The bird was seen annually, with most observaons within a
2-km segment of the American River. During two winters over 2022–2024,
it was also seen intermiently on a nearby pond in West Sacramento. The
hybrid showed intermediate characteriscs of both possible parents in
size and plumage, and it associated almost exclusively with Common
Goldeneyes, as is typical for this hybrid type. The lifespan of this hybrid is
unusually long compared to either parent species.
Hybrids birds are of interest because their frequency, viability, survival,
and reproducve success can indicate phylogenec relatedness among
parental types (Short 1972, McCarthy 2006). They also may indicate
introgression of parental species (i.e., the gradual movement of genes among
species through hybridizaon, such as in the Spoed Owl (Strix occidentalis)
and Barred Owl (S. varia; Hanna et al. 2019), and changes in habitat and
threats to species’ status. Overall, hybrids are rare, represenng an esmated
0.074% of all birds, and the proporon is much lower when the most common
hybrids among several Larus gulls and between Mallards (Anas platyrhynchos)
and related species are excluded (Justyn et al. 2020).
A male Buehead (Bucephala albeola) x Common Goldeneye
(B. clangula) hybrid was observed wintering over 10 seasons (2014–2024) on

52 Central Valley Birds, Summer 2024
the American River in Sacramento County, California, and at a pond in
adjacent Yolo County. We describe the hybrid and its behavior, site delity,
movements, and longevity. We also review the paern of occurrence of
hybridizaon of these two species in the region and, more broadly, discuss
potenal factors that may lead to hybridizaon.
STUDY AREA
The hybrid was observed at two Central Valley California locaons that
were 16 km apart. Most observaons were in the lower American River within
the Sacramento metropolitan area, Sacramento County, California. The lower
American River ows within a regional urban parkway from Lake Natoma in
the east to the conuence with the Sacramento River adjacent to downtown
Sacramento. The main area occupied by the hybrid was a 2-km secon of the
river upstream of Wa Avenue adjacent to the Waterton Way access (17 km
upstream of the conuence with the Sacramento River) to near Rio
Americano High School (hps://regionalparks.saccounty.gov/Documents/
ParkwayMap.pdf). The river splits in this area to ow around several islands,
which creates a set of side channels and backwater areas with varied water
depths and ow velocies from calm to rapid.
Based on bird counts conducted annually in December by the American
River Natural History Associaon, the lower American River supports average
winter populaons of nearly 700 Common Goldeneyes and 150 Bueheads
(Airola et al. 2023). During winter, the 2.4-km secon used most oen by the
hybrid typically supported 75–125 Common Goldeneyes and 20–90
Bueheads (ebird.org). Both species using this area forage on the river during
the day and roost at night at Arden Pond within the William P. Pond
Recreaon area (Airola et al. 2023), 1.5 km upstream of the main areas used
during the dayme by the hybrid.
The second occupied locaon is a 3.5-ha Stonegate Pond, a stormwater
detenon pond at Stonegate Drive and Hoopa Road in a residenal area of
West Sacramento, Yolo County. The permanent pond is 16 km west-
southwest of the center of the site of the hybrid’s occurrence on the
American River. The pond is mostly over 1 m deep (i.e., too deep to support
growth of caails, Typha lafolia), but with a shoreline of caails.
METHODS
We assembled and summarized eBird records (ebird.org) and our notes
of the hybrid over 2014–2024. In winter 2023–2024, we conducted more
extensive and coordinated surveys at the two occurrence sites to document
movements of the bird between them. We studied the bird in the eld and in
photos and video footage and used the literature to idenfy and compare the
characteriscs and behaviors of the hybrid to those of the Common
Goldeneye and Buehead.

Volume 27 Number 2 53
RESULTS
Descripon and Behavior
Phenotypic characteriscs of male Bueheads, Common Goldeneyes,
and the hybrid are summarized in Table 1. The most disncve feature of the
hybrid is its facial paern (Figure 1). The amount of white on the head was
more extensive than on a Common Goldeneye. White extended across most
of the lower two-thirds of the head, but the forehead and crown of the head,
extending down to the eye, were black, as in a goldeneye. Notably, the white
on the lower poron of the head connected to the neck and body (Figure 1),
which is uncharacterisc of either parent species, but typical of this hybrid
combinaon (Finley and Huot 2010, Reeber 2016). The facial paern had two
disncve black extensions into the white patch, from the chin and back of
the neck. These markings have remained idencal from year-to-year. Overall,
this hybrid’s markings were similar to those reported and shown by other
hybrids of these species observed elsewhere in North America (Finley and
Huot 2010, Reeber 2016, ebird.org).
Table 1. Comparison of characteriscs of male Buehead, Common Golden-
eye, and the hybrid.
Character Buehead Common Goldeneye Hybrid
Facial marking Large white
patch
Small white patch Intermediate white
patch extending to
neck and body
Body size Small Large Intermediate
Eye color Black Golden-yellow Golden-yellow
Head shape Rounded Peaked Slightly peaked
Head
iridescence
Purple, violet,
orange, yellow,
green
Green Green with small
amount of purple
Bill color Bluish Black Black
Bill size and
shape
Small, less
sloped
Large, more sloped Intermediate size
and sloping
Courtship
display
Head-bobbing Head lted back
90 degrees
Both head-bobbing
and head lted
back, but only to
45 degrees

54 Central Valley Birds, Summer 2024
Figure 1. Male Buehead x Common Goldeneye observed over 2014–2024 on the
American River, Sacramento County and at Stonegate Pond, Yolo County,
California. Photographed 28 January 2024 on the American River.
Photo by Andrea Willey.
Figure 2. Hybrid Buehead x Common Goldeneye with (le to right) Common
Goldeneye female, subadult male, and adult male. Note the slightly smaller size
and more rounded head shape of the hybrid. Photographed on American River
28 January 2024. Photo by Andrea Willey.

Volume 27 Number 2 55
The hybrid has several other physical characteriscs derived from both
parent species as well as some intermediate characteriscs. The hybrid
appeared to be smaller than a male Common Goldeneye and with a
proporonately shorter neck (Figure 2). Its eye was yellow as in a goldeneye
rather than black as in a Buehead (Figure 1). The head was peaked and
triangular shaped, but less so than for a Common Goldeneye, and less
rounded than for a Buehead (Figure 3). The head usually showed only green
iridescence like a goldeneye, with the purple iridescence of a Buehead
visible only occasionally on the forehead region. The bill was dark gray to
black like a goldeneye and lacked the bluish and violet colors of a Buehead.
The bill was similar in length and height to a goldeneye and longer and more
massive than in a Buehead.
Figure 3. Buehead x Common Goldeneye hybrid with Buehead, showing the
hybrid’s larger size, more peaked head, and larger dark bill. Photo taken
19 February 2024. Photo by Chris Conard.
In groups of other Common Goldeneyes, the hybrid regularly performed
the typical goldeneye head-throwing display, in which the head is thrown
back 90 degrees, so the bill points vercally (Eadie et al. 1995), except that
the hybrid only lted his head back to about a 45-degree angle and followed
this will a head bob display (hps://youtu.be/Hp01WABa5Vs; 11 February
2024). The hybrid was seen performing a longer sequence of the typical
Buehead head-bobbing display (Erskine 1971, Gauthier 2014) with a group
of typically displaying Common Goldeneyes at Stonegate pond
(hps://youtu.be/5twfPs0DJyg?si=AWDSA0Z-JDkKYnH-; 8 January 2024).

56 Central Valley Birds, Summer 2024
The hybrid was reported in eBird or observed by us on a total of 71 days
over the 10-year period connuing through 21 February 2024. During 20
reports when associated species were reported, it was consistently associated
with Common Goldeneyes (19 records, including eight mes when it was
associated with a female). The hybrid was observed associang with a female
Buehead only once. The hybrid dove to feed, as both parental species
typically do.
During 2024, A. Willey and J. Langham observed two dierent goldeneyes
in the same area of the American River as the hybrid that showed larger
patches of white on the face than is typical for Common Goldeneyes (Figure
4). Ospring would not be expected to overwinter with male parents, since
males abandon females aer nesng begins. There is no way of knowing,
however, if these individuals are backcrosses between the hybrid and a
female Common Goldeneye, which would suggest reproducve success of the
hybrid, or simply a goldeneye with a plumage color aberraon.
Figure 4. Hybrid Buehead x Common Goldeneye with one of two Common
Goldeneyes with anomalous facial markings seen in the same secon of the
American River, 28 January 2024. Photo by Andrea Willey.
Figure 5.
Common Goldeneye x
Buehead hybrid at
Stonegate Pond,
12 February 2023,
showing characterisc
markings of the hybrid
seen on the
American River.
Photo by Kirk Swenson.

Volume 27 Number 2 57
Site Fidelity and Movements
American River Occurrence. The hybrid was rst reported in eBird on the
American River on 4 December 2014 and has been reported there in every
winter through 2024. The hybrid was observed primarily on the American
River (59 records), with all but two records within the 1.5-km secon of the
river. The two observaons along the river outside of this area were 7.9 and
10.6 km downstream.
The number of records there over the 10 winter seasons varied from one
(2021–2022) to 14 (2014–2015) per year. The bird was seen as early as
9 November and as late as 14 March. Most records (91%) occurred between
1 December and 22 February, with only one record each in November and
March (2017 and 2015, respecvely).
Stonegate Pond Occurrence. The hybrid was not detected on Stonegate
Pond during the winters of 2014–2015 through 2021–2022, when Common
Goldeneyes were detected on 114 dierent days there (ebird.org). The hybrid
(idened as the same bird based on marking paerns in Figure 5) was
detected on 12 dierent days during the winters of 2022–2023 and 2023–
2024. The hybrid was seen there as early as 4 December and as late as
13 February (both dates in 2023).
Movements between Sites. In winter 2022–2023, the hybrid had last
been seen on the American River on 1–4 December and was then observed at
Stonegate Pond on eight days over a 53-day period from 23 December 2022
through 13 February 2023. It was not seen thereaer that winter at either
site. In winter 2023–2024, the hybrid made at least three trips between
Stonegate Pond and the American River. It was rst seen on 4 December 2023
at Stonegate Pond before it was found on the American River east of Wa
Ave. on 17 December. It then was seen back at Stonegate Pond from
7–9 January and again on the American River from 13 January through
21 February. The lack of overlap in reporng dates at the two locaons over
both winters supports the conclusion that it was a single individual.
DISCUSSION
Longevity and Site Fidelity
The presence of the same adult hybrid for over 10 years on the American
River is a noteworthy record of longevity and site delity. The average
lifespan of Common Goldeneyes is 3.7 years (Eadie et al. 1995) and for
Bueheads is 4.5 years (Gauthier 2014). Annual adult survival ranges from
61–67% for both species, which suggests that only about 1.1–2.7% of adults
live to this age (i.e., = 0.619 to 0.679). The oldest recorded Common
Goldeneye was 17 years-old and the oldest known Buehead was over
18 years-old (Eadie et al. 1995, Gauthier 2014). The use of the same small

58 Central Valley Birds, Summer 2024
stretch of the American River over all these years, and the apparent novel
movements to Stonegate Pond aer eight years of being seen only at the
American River are noteworthy.
Hybrid Frequency
Hybrids between the Buehead and Common Goldeneye were
unreported unl recent decades. The Birds of the World accounts by Eadie et
al. (1995) and Gauthier (2014), did not report any known hybridizaon,
although images of hybrids reported in eBird have been recently added to the
accounts. The rst hybrid records, from 1999–2010, were reported by Finley
and Huot (2010) and hybrids were noted by Reeber (2016). (A hybrid
observed by D. Airola in 1984 was not posted to eBird unl 2024).
A recent analysis of hybrids of all species reported in eBird idened 264
reports of Buehead x Common Goldeneye hybrids over 2010–2018, a
combinaon that was ranked as the 45th highest among 214 hybrid types
(Justyn et al. 2020). These reports, however, included mulple reports of the
same individuals. A more recent search of eBird idened a total of 564
reports of hybrids between these species (J. Eadie, pers. comm.). Although
many of these reports are of the same bird (including 65 records of the bird
we studied in the Sacramento region), the large number of records from 18
dierent U.S. states, four Canadian provinces, and even one from Japan,
supports the conclusion by Finley and Huot (2010) that hybridizaon,
although extremely rare, occurs regularly.
Buehead x Common Goldeneye hybrids have been reported elsewhere
in the nearby Central Valley, including White Slough Water Treatment Plant,
San Joaquin County (1996); Lake Solano, Yolo/Solano counes (2008–2010),
and Davis, Yolo County (2023) (Finley and Huot 2010, www.ebird.org). Hybrid
individuals reported elsewhere in California by these sources include: Lake
Almanor, Plumas County (1984, 2022); Berkeley Marina, Alameda County
(2006); 3rd Avenue Marsh, San Mateo County (2014); Buckley Ponds, Inyo
County (2016, 2021); Parker Dam, San Bernardino County (2018); and Napa-
Sonoma Marsh Wildlife Area, Napa County (2024).
The general rarity of the hybrid’s occurrence in California is indicated by
the presence of only 10-12 individuals known over a 41-year period
(depending on whether the Paradise Beach and 3rd Avenue records and two
Buckley Ponds records were the same or dierent individuals). All the hybrids
in California documented by photographs, except the bird reported in Davis,
were males with plumage like the American River bird.
Whether the increase in reported hybrids indicates an increase in
hybridizaon over me is uncertain. Johnsgard’s (1960) review of waterfowl
hybridizaon, as well as Gauthier’s (1993) and Eadie’s (1995) inial versions of

Volume 27 Number 2 59
the Birds of the World accounts, did not idenfy any Buehead x Common
Goldeneye hybrid records. Johnsgard (1960) recognized that the lack of
records could have reected the species’ absence in capve husbandry
compared to other waterfowl and their secondary importance as hunted
species in this pre-internet and pre-eBird era. Finley and Huot (2010)
idened a hybrid of these species in Brish Columbia (2009) and used
internet sources to idenfy nine other separate records (1999–2010), which
were not incorporated into Gauthier’s (2014) Birds of the World account
update. At that me Finley and Huot (2010) concluded that the increase in
sighngs was an arfact of an increase in birding, digital photography, and
increased communicaon through the internet, rather than a true increase in
rates of hybridizaon. Despite connued increases in reported records since
2010, this explanaon sll appears to be valid.
Although Common Goldeneye and Buehead pairs may reestablish pair
bonds in mulple breeding years (Eadie et al. 1995, Gauthier 2014),
goldeneyes do not maintain pair bonds beyond the incubaon period
(Bellrose 1976). As a result, they apparently do not migrate and winter as
family groups. Buehead adults and subadults migrate at dierent mes and
appear to segregate into dierent parts of their wintering ranges (Erskine
1971), suggesng lack of family cohesion. Therefore, other than observing the
male hybrid associang with female goldeneyes, we have no way of knowing
of whether the hybrid had aempted to breed with a female of either species
and, if so, whether breeding was successful.
Causes of Hybridizaon
The potenal factors that can lead to hybridizaon are unknown, but
several possibilies exist. Bueheads are known to “dump” eggs into other
female’s nests (Gauthier 1987). Egg-dumping by a Buehead into a Common
Goldeneye nest may have caused the reared male Buehead young to
imprint on, and then mate with, a goldeneye female. Such a pairing has been
observed (Finley and Huot 2010). Male Common Goldeneye x female
Buehead pairs would be less likely to occur under this hypothesis because
male Common Goldeneyes end their parental dues aer egg-laying (Eadie et
al. 1995), so female Buehead ospring hatched from egg dumping into a
Goldeneye nest would not have a male model on which to imprint.
Another potenal cause of hybridizaon is a lack of conspecic mates
from which to choose (Short 1971). Although the breeding ranges of the
Buehead and Common Goldeneye broadly overlap across North America
(Gauthier 2014, Eadie et al. 1995), the Buehead is characterized as a
“scarce” breeder in much of its range. Low Buehead density may force them
to mate with Common Goldeneyes in certain areas. The occurrence of a
wintering hybrid in Japan, where the Common Goldeneye occurs regularly,

60 Central Valley Birds, Summer 2024
but the Buehead rarely occurs, is consistent with the idea that mate choice
limitaon at the edge of the Buehead’s breeding range may have induced
hybridizaon in this case.
ACKNOWLEDGEMENTS
We thank those who reported observaons of the hybrid in eBird,
including Gil Ewing, Cli Hawley, Jim Pompy, R.M. Yoshihara, Mike Guard,
Zane Picus, Kirk Swenson, Yvee MacDonald, and Rachel Lawrence. Thanks
also to Kirk Swenson for his photograph. We thank John Trochet, and
P. Lavretsky for helpful review comments. We thank John Eadie for
summarizing eBird data and providing several key suggesons and references
that greatly improved the paper. Thanks also to those at the Cornell Lab of
Ornithology who maintain the eBird database.
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