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White-tailed Laurel Pigeon Columba junoniae exploiting pollen and nectar of the invasive Century Plant Agave americana

Authors:
  • Grupo de Ornitología e Historia Natural de las islas Canarias
  • Grupo de Ornitología e Historia Natural de las islas Canarias

Abstract and Figures

Le Pigeon des lauriers Columba junoniae exploitant le pollen et le nectar de l’Agave américain Agave americana. Les observations ont été réalisées durant l’été 2019 sur l’île de Tenerife, dans une zone de transition entre la végétation thermophile et la forêt de lauriers. En étant perchées sur les fleurs ou la tige de l’ombelle, les oiseaux picoraient et consommaient des anthères et, dans une moindre mesure, du nectar, qui est une ressource trophique inhabituelle chez les Columbiformes. Les pigeons ne semblent pas contribuer à la reproduction de la plante.
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White-tailed Laurel Pigeon exploiting the invasive Century Plant: Siverio et al.
Bull ABC Vol 28 No 1 (2021) – 71
White-tailed Laurel Pigeon Columba junoniae exploiting pollen
and nectar of the invasive Century Plant Agave americana
Felipe Siverio
a
, Beneharo Rodríguez
a
and José Juan Hernández
b
Le Pigeon des lauriers Columba junoniae exploitant le pollen et le nectar de l’Agave américain Agave
americana. Les observations ont été réalisées durant l’été 2019 sur l’île de Tenerife, dans une zone de
transition entre la végétation thermophile et la forêt de lauriers. En étant perchées sur les fleurs ou la tige de
l’ombelle, les oiseaux picoraient et consommaient des anthères et, dans une moindre mesure, du nectar, qui
est une ressource trophique inhabituelle chez les Columbiformes. Les pigeons ne semblent pas contribuer
à la reproduction de la plante.
Although there are no specialist nectarivorous
birds on the Canary Islands, several endemic
and exotic plants are visited opportunistically
by native passerines, mainly by Canary Islands
Chiffchaff Phylloscopus canariensis (e.g. Valido et
al. 2004, Ollerton et al. 2009). On Tenerife, for
example, the inflorescences of the Century Plant
Agave americana attract many birds, with at least
eight species, including Common Raven Corvus
corax, recorded as seeking its nectar (Rodríguez et
al. 2015). This conspicuous plant, which is native
to the southern USA and Mexico, and perhaps
legitimately visited there by bats and birds (see
Knudsen & Tollsten 1995), was introduced in the
Canary Islands probably in the 16th century and
is highly invasive (Badano & Pugnaire 2004, Silva
et al. 2008). White-tailed Laurel Pigeon Columba
junoniae and Bolle’s (Dark-tailed Laurel) Pigeon
C. bollii, which are endemic to the central-western
Canary Islands, are often considered to be potential
visitors to Century Plant flowers because their diet
is based on fruits, leaves and flowers (Martín et al.
2000), and White-tailed Laurel Pigeon has already
been reported to consume Century Plant flowers,
but no details were provided (Martín et al. 2020).
Following occasional sightings of White-tailed
Laurel and Bolle’s Pigeons visiting Century Plant
inflorescences on La Palma (Siverio et al. 2016)
and Tenerife (in September 2018), we decided to
observe these interactions more closely. During
summer 2019, we made observations at two
localities in north-west Tenerife, both typified by
a degraded transition zone between thermophilous
and laurel forests, where several flowering Century
Plants and both pigeon species were present. On
10 August we undertook four hours of intensive
observation (06.50–10.50 hrs) using a 20–60×
telescope c.140 m from the plants to quantify
foraging behaviour. Furthermore, between 30
July and 16 August we made c.43 hours of non-
Figure 1. Immature White-tailed
Laurel Pigeon Columba junoniae
eating anthers of a Century Plant
Agave americana while perched
on one of the umbels; note how
most of the anthers and some
stigmas have already been eaten
(Beneharo Rodríguez)
Pigeon des lauriers Columba
junoniae immature mangeant
des anthères des inflorescences
de l’Agave américain Agave
americana perché sur l’une des
ombelles ; remarquer comment
la plupart des anthères et certains
stigmates ont déjà été mangés
(Beneharo Rodríguez)
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White-tailed Laurel Pigeon exploiting the invasive Century Plant: Siverio et al.
72 – Bull ABC Vol 28 No 1 (2021)
systematic observations from hides sited 5–15m
from plant inflorescences, usually in bouts of c.3.5
hours/day between dawn to noon (once we stayed
until mid-afternoon) during which we also had
the opportunity to obtain photographs.
At least 23 visits (visitation rate = 5.75 per
hour) by White-tailed Laurel Pigeons to three
inflorescences of Century Plant were recorded
during the four hours on 10 August; no other
bird species visited the flowers during this period.
Thirteen of these pigeons’ visits, which were
observed from start to end, lasted a mean 6.6
minutes ± 4.6SD (range 2–17) and were directed
at 3.3 ± 1.8 SD inflorescence umbels on average
(range 1–6). While perching on flowers (c.57%)
and on the umbel branch, the pigeons spent c.85%
of the time pecking and eating mainly anthers
(Fig. 1; also stamens, stigmas and petals), and to
a lesser extent consuming nectar (c.10%) directly
from the floral receptacles (Fig. 2). During the
remaining time, the perched birds were inactive,
apparently observing the movements of other
pigeons in the environs: at least nine White-
tailed Laurel and two Bolle’s Pigeons were seen
at the site. Visits were also most frequent at dawn
(69.6% during 06.50–08.50 hrs), progressively
decreasing thereafter.
Combining our systematic (four hours) and
opportunistic observations (c.43 hours), we
occasionally noted up to five White-tailed Laurel
Pigeons fed simultaneously in a single floral scape.
Although we observed only adult and immature
White-tailed Laurel Pigeons visiting Century
Plant flowers, we cannot eliminate that Bolle’s
Pigeons also, sporadically, visit these flowers as
we observed them a few times perched on floral
scapes. The majority of pigeon–flower interactions
were antagonistic as the birds appeared to consume
part of the flowers’ reproductive organs, especially
when the same umbel was visited several times
by different individuals. Pigeons appear to prefer
some floral scapes over others, possibly those
in concealed sites, such as ravines or slopes not
directly visible from roads.
Although White-tailed Laurel Pigeons and
Century Plants often share the same habitat
in Tenerife, it appears that only rarely does
the interaction go beyond use of the floral
scape as a perch. Probably ‘real’ interactions
are the result of continuous learning behaviour
initiated by some individuals which discovered
that the inflorescence (mainly anthers) represents
a significant temporary trophic resource (e.g.
in July–September, Rodríguez et al. 2015),
complementing their principally frugivorous diet
(Martín et al. 2000). Additionally, the diluted
nectar of Century Plant flowers, with c.15% sugar
concentration (Rodríguez et al. 2015), could
supply the water requirements of these birds in
some circumstances (see Nicolson et al. 2007),
especially given that in summer, when the plant
blooms, this resource is less abundant (Rodríguez
et al. 2015).
To our knowledge, nectarivory in
Columbiformes is quite unusual (e.g. Baptista et al.
1997, Symes 2010). Apart from the case described
Figure 2. Adult White-tailed
Laurel Pigeon Columba
junoniae feeding on diluted
nectar from a Century Plant
Agave americana flower; note
that many of the anthers
appear to be mature (José
Juan Hernández)
Pigeon des lauriers
Columba junoniae adulte
se nourrissant de nectar
dilué d’une fleur de
l’Agave américain Agave
americana ; remarquer que
de nombreuses anthères
semblent mûres (José Juan
Hernández)
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White-tailed Laurel Pigeon exploiting the invasive Century Plant: Siverio et al.
Bull ABC Vol 28 No 1 (2021) – 73
here, the only two examples of nectar-feeders we
are aware of are the Eared Dove Zenaida auriculata
noronha, endemic to the archipelago of Fernando
de Noronha (north-east Brazil), and White-
winged Dove Z. asiatica mearnsi of the south-west
USA and western and central Mexico. These
columbids are among the main pollinators of the
native Erythrina velutina (Sazima et al. 2009) and
Saguaro Carnegiea gigantea plants (Alcorn et al.
1961), respectively, when they visit their flowers
seeking nectar. Nectarivory by White-tailed
Laurel Pigeons may perhaps lead to pollination
of Century Plant flowers, particularly when the
birds retrieve nectar while perched on the umbel
and come into contact with anthers and stigmas.
However, if during most visits floral organs are
destroyed, the plant’s sexual reproductive cycle
may be disrupted.
Acknowledgements
We are indebted to Arlette Aubier for helping to produce
the French summary. Thanks also to Craig Symes, Guy
Kirwan and Ron Demey for their comments that
improved the text.
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a
Canary Islands’ Ornithology and Natural History
Group (GOHNIC), La Malecita s/n, E-38480
Buenavista del Norte, Tenerife, Canary Islands, Spain.
E-mail: fsiverio@gohnic.org
b
C/ La Habana, Edificio Las Vistas nº 8, Apto. 4º izq.,
E-38650 Los Cristianos, Tenerife, Canary Islands, Spain.
Received 21 May 2020; revision accepted 3 October
2020.
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Article
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Capsule: Flowers of an invasive plant species are more visited by native birds than flowers of ornithophilous endemic plants. Aims: To describe the bird guild and its behaviour visiting the century plant Agave americana in an insular environment and to determine which factors are affecting visitation rates. Methods: We noted number and species of birds visiting inflorescences on Tenerife, Canary Islands. We used multimodel inference of generalized linear models to analyse the factors affecting the number of visits and the visitor species richness. Results: Eighty-one per cent of inflorescences were visited by eight native bird species. All species fed on nectar and only the Atlantic Canary fed also on pollen. Foraging behaviour varied among species. Visitation rate increased with density and diversity of birds and flower characteristics and decreased through the day. The number of species visiting the inflorescences increased with diversity and density of birds in the surroundings and decreased through the day. Conclusion: The native bird community uses the invasive century plant as a feeding resource at a higher rate than it uses endemic ornithophilous plants. This could have negative effects for the pollination of endemic plants, but positive effects for birds.
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