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

  • 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
, Beneharo Rodríguez
and José Juan Hernández
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
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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.
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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Received 21 May 2020; revision accepted 3 October
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ResearchGate has not been able to resolve any citations for this publication.
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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.
Full-text available
Recent studies have shown that Macaronesia has considerable problems with exotic species, particularly those considered as invasive. For instance, in the Azores more than 60% of the vascular plant flora consists of non-indigenous species (Silva & Smith 2004, 2006). Several plants are presently considered to be serious threats not only to the conservation of the Azorean endemic flora and native plant communities, but also to the conservation of bird species, namely the Azores bullfinch (Pyrrhula murina) and of arthropods (Borges et al. 2006). In Madeira Archipelago, species like the black rat (Rattus rattus) and the domestic cat (Felis silvestris catus) are known to have a strong negative impact on populations of native birds. In the Canaries, about 11% of the terrestrial biota corresponds to alien species, and some recent introductions originated some social alarm, namely the recent naturalization of a species of snake (Lampropeltis getula) in Gran Canaria. However, of the considerable number of introduced species, how many are considered as really invasive (i.e. they are not only naturalized but are presently causing a negative impact on the Macaronesian biota)? Among those species, which are amenable to control or eradication? Which species should be considered priorities for control actions and other measures because they are causing impact but are still possible to control or eradicate? For instance, in Canaries the Barbary ground squirrel (Atlantoxerus getulus) is considered an emblematic invasive alien species (IAS), but is it the top-ranking invader in Macaronesia? French Hydrangea (Hydrangea macrophylla) is a touristic icon in the Azores, but is now also considered as an invasive alien species. What is the real impact of the different species of alien rodents in Macaronesia? Although negative impacts have been a concern, should positive impacts also be considered? For example, several alien species still have and will most probably continue to have an important role in the islands’ economy or as game species. This book aims to answer some of these questions. It is a first attempt to present information regarding alien species in the European region of Macaronesia in a systematic way. Undoubtedly, this is a difficult task, due to differences regarding legislation but also to the differences in the general treatment given to IAS in the different archipelagos. A standard set of criteria was designed and applied to those species considered as naturalized and occupying natural and semi-natural habitats. A first set of criteria was used to score the effect on biodiversity values, in terms of species and habitats, which are being affected by the invasive species. A second set of criteria was used to score the feasibility of control or eradication of the invasive species. In this second set of criteria we also included items reflecting the social importance of the species concerned. The application of both sets of criteria has allowed identification of the most noxious IAS in Macaronesia and also the ranking of those species according to a management priority. This is of considerable importance, since, due to the large scale of the IAS problem not only in Macaronesia but globally, it is not possible to control every introduced species. Resources will have to be allocated to those species that are still possible to control or eradicate with sustainable costs. Although the criteria were applied by experts from each archipelago, a global Macaronesian approach was possible after a thorough analysis and careful treatment of the data from each archipelago, this being the main objective of the book. This book is also intended to serve as a tool to raise awareness of the problem of IAS. In fact, island ecosystems have been considered as more susceptible to IAS than continental systems, largely due to the small scale of the islands and to peculiarities of island biota which make them more susceptible to foreign competitors, predators and pathogens. However, islands, particularly European islands, are important hotspots for biodiversity, and the preservation of this natural heritage is currently also dependent on the implementation of effective measures to contain IAS
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Species of the pantropical genus Erythrina (Fabaceae) are visited by perching and/or hovering birds in the mainland. At the oceanic island of Fernando de Noronha, north-eastern Brazil, we found that Erythrina velutina Willd. blooms during the dry season and the flowers are visited by a small vertebrate assemblage. Flowers last 2 days and their stigmas remain receptive, although only first-day flowers produce nectar. Nectar is dilute and produced copiously. All terrestrial native vertebrates (three of them endemics), the dove Zenaida auriculata noronha, the perching birds Vireo gracilirostris and Elaenia ridleyana, and the lizard Euprepis atlanticus are regular visitors and pollinators. The features of E. velutina conform to those of passerine-pollinated species within the genus. Its nectar is a resource sought by the vertebrates, which visit the inflorescences from dawn to sunset. Since none of the visitors depends on nectar as a major food source, the flowers are likely to serve a dual purpose, i.e. water balance and energy intake, similarly to the findings for some Erythrina species in Neotropic and Palaeotropic mainlands. However, E. velutina is the only species within the genus that is visited and pollinated by doves and lizards.
Full-text available
Aims Several bird-pollinated or ornithophilous flowers are present on the Macaronesian archipelagos, the Canary Islands and Madeira, but absent from nearby NW Africa and Europe. In Macaronesia, no specialist nectar-feeding birds are found, but several generalist passerine bird species visit flowers for nectar. Two hypotheses attempt to explain the origin and evolution of ornithophily in the Macaronesian flora. According to 'the island de novo hypothesis', bird-flowers evolved from mainland insect-pollinated ancestors after island colonization. Alternatively, ancestors of the ornithophilous Macaronesian plant species evolved bird-flowers before reaching the islands ('the relict hypothesis'). In this study we first compile information of Macaronesian bird-flower interactions from the literature and our own field observations. Secondly, we discuss the two hypotheses of origin of ornithophily in the light of evidence from recent molecular plant phylogenies, palaeontology, historical biogeography of the African avifauna and flora, and present-day ecological patterns.
The chemical composition of floral scent in eight bat-pollinated species belonging to six different plant families was investigated. Floral scent was collected by headspace trapping using porous adsorbents and the chemical composition determined by coupled gas chromatography-mass spectrometry. In all species except one the floral scent was found to include sulphur-containing compounds, of which several are reported for the first time in floral scents. Three species contained mushroom-like smelling fatty acid derivatives with a C8-skeleton. Such flowers may be recognized by pollinators as humid environments in otherwise dry surroundings. The presence of similar or chemically closely related sulphur containing compounds in floral scent of bat-pollinated plant species from differing families may represent a case of convergent evolution in scent composition and an adaptation to attract this specific group of pollinators with similar sensory preferences.
Several mechanisms have been proposed to explain the success of invasive species in new environments. A species may become invasive when a new site provides the potential for positive rates of population growth. This may be the case of several Agave species introduced to Spain in the 1940s. In this paper we document factors that promote large increases of populations of these species, and their effects on native plant communities in two sites of SE Spain. Results showed higher rhizome and bulbil production, and higher establishment rates by agaves in sandy soils than in clay soils. In their native habitats, agaves have low establishment rates and sandy soils are rare. This suggests that sandy soils are an opportunity which releases the clonal reproduction of Agave. The effects of agaves on the physiological performance and reproduction of native species were negative, positive or neutral, depending on the size and rooting depth of neighbours. Assemblages of native species growing within Agave stands had lower diversity than non-invaded sites. Our data show that Agave stands have positive growth rates in SE Spain, and suggest that sandy soils are a niche dimension enhancing the invasion in these new habitats.