First Documentation of Successful Breeding for the Anna’s Hummingbird in Idaho

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76 Western Birds 52:76–79, 2021; doi 10.21199/WB52.1.6
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FIRST DOCUMENTATION OF
SUCCESSFUL BREEDING FOR
THE ANNA’S HUMMINGBIRD IN IDAHO
BRYCE W. ROBINSON, Cornell Lab of Ornithology, Cornell University, Ithaca,
New York 14850; bwr46@cornell.edu
JESSICA J. POLLOCK, HEIDI WARE CARLISLE, and HEATHER M. HAYES,
Intermountain Bird Observatory, Boise State University, Boise, Idaho 83725
JANICE ENGLE, 3046 E. Stone Point Dr., Boise, Idaho 83712
Currently, the Anna’s Hummingbird (Calypte anna) breeds along the west coast
of North America from Baja California to British Columbia and east into inland
areas of California, Arizona, New Mexico, Oregon, and Washington (Clark and
Russell 2012). The current distribution is a result of 80 years of range expansion
out of Baja and coastal California, largely facilitated by urbanization, landscaping
with non-native plants, and supplementary feeding (Greig et al. 2017, Battey 2019).
Pollock et al. (2021), summarizing the recent increase in the numbers wintering
in Idaho, illustrated that the species’ range continues to expand. This increase in
winter numbers over time mirrors the trend in Arizona in the 1960s, when the es-
tablishment of a breeding population followed wintering (Zimmerman 1973, Clark
and Russell 2012). Pollock et al. (2021) further suggest that Anna’s Hummingbird
may now be a sparse year-round resident in parts of Idaho, primarily the greater
Boise metropolitan area. Given the recent trend in Idaho that includes an increase
in summer numbers in the past three years (ibid.), the establishment of a breeding
population in the state seems possible, even probable.
Rudeen and Bassett (2016) presented evidence implying that Anna’s Hum-
mingbird has already bred in Idaho: the captures of multiple individuals in juvenile
plumage in August, a gravid female at the same location in two consecutive seasons,
and a putative hybrid male Anna’s × Calliope Hummingbird. Given this evidence,
they reasonably expected documentation of nesting to be imminent.
On 14 July 2020, Engle discovered an adult female Anna’s Hummingbird at-
tending a nest containing two nestlings in the front yard of her home in the Warm
Springs Mesa neighborhood in southeast Boise (Figure 1). The nest was situated on
a horizontal limb of a Rose of Sharon tree (Hibiscus syriacus), 3 m high and only 2
m from the front window of the home. Engle’s home sits at 930 m elevation, in an
urban neighborhood adjacent to the foothills, and with a landscaped yard including a
fountain, pond, multiple flowering plants, and hummingbird feeders. We monitored
the nest daily until the nestlings began to climb from the nest on 17 July (Figure 2).
Both young fledged successfully on the morning of 18 July.
Following the fledging of the young, we attempted to capture the adult and
fledglings at Engle’s feeders. Unfortunately, we were able to capture only the adult
female, which we discovered was banded (see M07787 in Table 1 in Pollock et al.
2021). This female was first captured and banded on 25 January 2019 at a home 0.5
km from the location where she nested at Engle’s home. She was recaptured the fol-
lowing winter on 17 December 2019 at the same location, and is among a growing
number of individuals whose site fidelity in Idaho over successive winters has been
confirmed (see Table 1 in Pollock et al. 2021). Interestingly, the homeowners did not
observe her at this location in either summer 2019 or 2020, despite the proximity
to the site of her nesting.
The identity of the male parent of these fledglings is unknown. As is general in

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F 1. Adult female Anna’s Hummingbird (Calypte anna) attending two nestlings
in southeast Boise, Idaho, 14 July 2020. This photograph represents the first
documentation of nesting of the Anna’s Hummingbird in Idaho.
Photo by Janice Engle
F 2. The two nestling Anna’s Hummingbirds on 17 July 2020, one day prior to
their successful fledging on 18 July.
Photo by Bryce W. Robinson

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hummingbirds, males of C. anna are not involved in brood care (Clark and Russell
2012), so it is not surprising we never observed a male in the area following the dis-
covery of the nest. However, Engle did observe an adult male Anna’s Hummingbird
at her feeders on 7 July, only 7 days before she discovered the nest. Alternatively, it is
possible that the female Anna’s was paired with a male Black-chinned Hummingbird
(Archilochus alexandri), the only hummingbird species that breeds commonly in the
Boise metropolitan area. Hybridization between A. alexandri and C. anna has never
been directly documented, although multiple birds that fit the expected appearance
of this hybrid have been photographed (see Black-chinned × Anna’s Hummingbird
at www.macaulaylibrary.org), and there is one specimen record (Banks and Johnson
1961). Nevertheless, from our observations and photographs of the juveniles (Figure
2), we assert that these are not a result of hybridization between C. anna and A.
alexandri. We reviewed photographs of fledglings and juveniles of both species avail-
able in the Macaulay Library, the detailed plumage descriptions in Howell (2003),
and the photographs of nestlings in figure 5 of Greeney et al. (2008) and compared
these to photos of the fledglings at Boise. The Boise fledglings differed from juvenile
Black-chinned Hummingbirds in being overall duskier in appearance, particularly
in the flanks, which had greenish feathers typical of Anna’s. The Boise birds also dif-
fered from A. alexandri in having densely marked throats and relatively dark heads.
Although wing shape was difficult to judge in our photos, we noted that the inner
primaries were not appreciably narrower than the outer primaries, as is seen in the
Black-chinned, and appeared to fit the shapes expected of C. anna. Additionally, the
shape of the exposed primaries differed from those shown in figure 5 of Greeney et al.
(2008), appearing relatively straight in the Boise birds and not substantially curved as
in the Black-chinned nestlings. Overall, the plumage of the Boise fledglings seemed
to fit the Anna’s Hummingbird, and did not appear to be intermediate between the
two species, as would be expected in first-generation hybrids.
The timing of this nesting is notable. Throughout its native range, the Anna’s
Hummingbird breeds from December to May (Clark and Russell 2012). At the
margins of its distribution in coastal Washington and British Columbia, nesting
begins slightly later, from January to February (ibid.). By taking the average periods
of incubation and nestling (16 and 20 days respectively; Clark and Russell 2012) and
backdating from the date of fledging on 18 July, we estimate the nest to have been
initiated on 12 June, an atypically late date by comparison to the dates reported
elsewhere throughout the species’ range. Anna’s Hummingbirds often raise multiple
broods in a single breeding season (Scarfe and Finlay 2001), and this nesting could
represent a second brood. The phenology we observed in Idaho is matched by the
first reported breeding of the species in southwestern Canada in 1958, which also
occurred in July (Campbell et al. 1990). More reporting and continued focus on the
species’ phenology of nesting at the margins of its range may uncover if the schedule
in these two instances is typical for extralimital breeders.
This first documented successful breeding of the Anna’s Hummingbird in Idaho
provides a marker on the chronology of the species’ range expansion into the state.
This chronology has thus far been well documented through the methods outlined
by Pollock et al. (2021). Continued focus and documentation of the increase in
numbers, as well as of further instances of breeding, will provide fine-scale details
to the ongoing range expansion experienced by this species since the urbanization
of the West accelerated in the middle of the 20th century. Investigations into the
provenance of Anna’s Hummingbirds wintering around Boise will provide further
clarity to the pattern of expansion into Idaho, and elsewhere.
We thank David Towner who initially reported M07787, the nesting female, in his
yard in December 2018, through the Intermountain Bird Observatory’s community-
science program of hummingbird reporting. We also thank Jay Carlisle, Daniel D.
Gibson, and Chris Clark for their helpful reviews of the manuscript.

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Accepted 20 November 2020