Study

The presence of nectar feeders reduces hummingbird visitation rates to two native shrubs Mexican sage Salvia mexicana and cardinal sage Salvia fulgens in a suburban park near México City, Mexico

  • Published source details del Coro Arizmendi M., Constanza M., Lourdes J., Ivonne F. & Edgar L. (2007) Effect of the presence of nectar feeders on the breeding success of Salvia mexicana and Salvia fulgens in a suburban park near México City. Biological Conservation, 136, 155-158

Summary

The use of hummingbird nectar feeders has increased as a result of people wanting to attract these birds to their gardens. Whilst feeders represent a rich food resource for hummingbirds, they might result in reduced visitation to plants. It has been suggested that locally, the presence of feeders could have a negative effect upon plant reproduction by decreasing the number of visits to flowers and hence pollen transfer, resulting in lower seed set. The study summarised here experimentally investigated hummingbird visitation to and seed production of two native Salvia shrub species in a suburban park near Mexico City where feeders had been placed in the vicinity of the plants.

Study area: Experiments were undertaken in two 300 m² areas of forest in Mexico City Ecological Park in October 2004 for Salvia mexicana and April 2005 for S.fulgens.

Hummingbird visitation: Visitation to flowers were recorded (species, number of flowers visited, visit duration and time of visit) for 10 plants without feeders and 10 with feeders. Observations were made from 07:00 to 15:00 h over 3 days.

Plant reproductive success: To assess reproductive success, 10 plants of each Salvia were selected and 10 flower buds (just about to open) were enclosed in net bags. Two nectar feeders were placed by each plant and then the bags were removed to expose the recently opened flowers. Plants with no feeders were treated similarly. After flowers closed in late afternoon, they were covered again with net bags; this was repeated for the life of each flower (4 days). After about a month, the fruit was collected and seeds counted.

S.fulgens flowers were visited by three hummingbird species, white-eared hummingbird Hylocharis leucotis, green violet-ear Colibri thalassinus and magnificent hummingbird Eugenes fulgens. The flowers on plants near a feeder had fewer visits than those without the feeder (average flowers/hour with feeder 3.2; without 7.0). Seed production was lower in plants near a feeder (average seeds/flower 1.6) than in plants without feeders (2.7).

S.mexicana flowers were visited by the same three hummingbird species (but only during the morning >< 07:00 to 11:00), and also by bees. Again, the flowers on plants near a feeder received fewer visits than plants without the feeder (average flowers/hour with feeder 3.5; without 11.5). Seed production was similar between treatments (average seeds/flower with feeder 2.01, without 2.05).

The authors conclude that in some urban and suburban areas, despite the fact that artificial feeders encourage higher densities of hummingbirds, overuse in gardens might cause problems for some specialist obligate hummingbird-pollinated native plant species. Therefore as a conservation measure, using native plants to attract hummingbirds to gardens in conjunction with sensible use of nectar feeders, is urged.


Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.sciencedirect.com/science/journal/00063207


 

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