2014 May – White-winged doves are key

cont…

gail-white-winged-dove-adult

White-winged doves fly here from wintering grounds in Southern Mexico. They arrive in April just as the creamy blossoms of the saguaro are breaking open and wafting alluring scent into the air. The doves replenish themselves with saguaro nectar containing water, sugar and protein. A sports drink couldn’t be better formulated to match their needs. In return, the doves carry pollen from one tall plant to another, enabling saguaro fertilization. A mature saguaro may produce 500 blooms in the spring. Each flower blooms for a single evening, opening up after dark and closing when the sun is high the following day. Nectar feeding bats get first dibs on the newly opened blossoms. Come dawn, white-winged doves feast at the flowers, joined by Gila woodpeckers and curved-bill thrashers. Bees also mob the sweet blooms.

White-winged doves mate in early May. Pairs build their flimsy nests in the highest branches of desert trees. Both parents take turns incubating the two eggs. The hatching of the eggs in June coincides perfectly with the fruiting of the saguaro.

Nestlings drink crop milk regurgitated by mom and dad for about four days. The parents soon transition the babies to the pulp and seeds of the saguaro plus seeds from a variety of other desert plants. By July, when the saguaro fruits are at their juiciest, the white- winged dove adults and young are feeding almost exclusively on this rich food source. According to scientific analysis of white-winged dove diet, “In July…the isotopic composition of the dove’s tissues was almost indistinguishable from that of the saguaro. In isotopic terms, breeding white-winged doves are warm, feathered fragments of saguaro flying about in the desert.” (1)

Saguaro fruits ripen at a time of extreme hot, dry conditions in the desert, so provide a lifeline for a wide range of desert animals, carrying them over until the monsoon season. Birds such as Gila woodpeckers, verdins, ash-throated flycatchers and cactus wrens help with seed dispersal, defecating viable saguaro seeds at roosting and nesting sites. This diversification is fortunate for the cactus, as the white-wing’s tough digestive system is brutal on its tiny seeds.

Doves do transfer some seeds when they carry bits of dripping saguaro fruit to their nestlings. Seeds dropped beneath nests await the promise of summer rains. Those that germinate and become seedlings benefit from the nest tree’s protection.

In September white-winged doves break off the cozy relationship with their cactus cohorts and migrate back to the southern regions of Mexico.

References and further reading:
(1) Saguaros and White-winged doves: the natural history of an uneasy partnership by Del Rio, Wolf and Haughey.

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