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Individual study: Supplementary feeding and its effect on pink pigeon Columba mayeri survival, Black River Gorges, Mauritius

Published source details

Jones C.G., Swinnerton K.J., Taylor C.J. & Mungroo Y. (1992) The release of captive-bred pink pigeons Columba mayeri in native forest on Mauritius. A progress report July 1987-June 1992. Dodo, 28, 92-125

Summary

The provision of an extra food supply, as a compliment to naturally available resources, is a method that has been used in enhancing the success of several species recovery programmes. Increases in survivorship, breeding activity, reproductive success and population size are just some of the benefits achieved by the provision of supplementary food.

As a result of habitat loss together with the adverse effects of introduced predators, the pink pigeon Columba mayeri, an endangered Mauritian endemic, suffered severe declines in population size and range. A captive breeding and release programme was established in 1987, in order to increase population size.

In order to promote survivorship and success of the released pink pigeons, supplementary feeding was an integral part of this recovery programme.

Pink pigeon releases: Between July 1987 and June 1992, 42 pink pigeons Columba mayeri were released at Plaine Lièvre in the Black River Gorges, south Mauritus.

Diet: Supplemental feed, following release, was similar to that provided whilst the birds were in captivity. A mixture of maize Zea mays, wheat Triticum aestivum, canary seed Phalaris canariensis, millet (fam:Gramineae), lentils Lens culinaris, and occasionally peas Pisam sativum and other seeds were provided.

Dispenser design: Food was provided on a ledge, spanning the width of the release aviaries. When the release hatch was opened, this encouraged the birds out of the aviary in addition to, later, luring them back into it. In September 1989, two feeding dispensers were erected close to the release aviaries. Food was given in two self-dispensing, covered hoppers, standing on raised platforms. The first platform consisted of four 10 cm × 2 m wooden poles with a 1.5 × 1.5 m platform on top. The second was a wigwam structure, consisting of three wooden poles (10 cm × 2 m), with a 1 m × 1 m platform on top. Both designs had tin cones placed around the poles which were at least 1 m above the ground, to deter rats Rattus sp.

Food provision: Supplementary food was provided in the afternoon on a daily basis from June 1987 to December 1987. Thereafter, the quantity and regularity of provision was gradually reduced in order to decrease dependence, and eventually ceased in February 1988. Feeding was recommenced in June 1988 when more pigeons were released, and has been provided ever since.

Monitoring: Released pigeons were fitted with individual colour ring combinations, as well as numbered metal rings. A daily record of each bird's presence was recorded. A more detailed study of supplementary food usage was carried out between 27 October 1991 and 15 March 1992, when data was collected on food usage from the released population.

Observations were carried out in 3-hour sessions from 06.00-18.00 hrs. In total, 231 hours over 34 days of observations were collected. Presence/absence data of birds visiting the hoppers were recorded using one-zero sampling (1 = presence, 0 = absence) with 1 min intervals.



Reliance on supplemental food: Sixteen different pink pigeons visited the hoppers daily during the duration of this experiment (October 1991 to March 1992). On average, they spent 20 min 30 sec at the feeding station each day. The frequency of visits (Fig. 1) to the hoppers increased during the last three hours of observations in the afternoon (between 15.01 and 18.00 hrs). These results suggest that birds foraged on naturally available foods mainly during the day, and fed on supplementary food at the end of the day in order to make up any deficit associated with natural foraging.

Reliance on supplementary food increased during a period of bad weather (February 1992 to March 1992) when high winds and heavy rainfall prevailed.

Other observations have highlighted the benefit of supplementary food to the population. For example, the week after a cyclone passed close to Mauritius on 28 to 29 January 1989, a female bird that had not been seen at the release/feeding site for one year, returned to feed on the supplementary food for several weeks. Presumably this was in response to a dearth of available wild food at this time due to the cyclone.

During the period when supplementary food was stopped completely from March 1988 to June 1988, only two of seven birds were seen again at the feeding station, even after intensive searches and the authors suggested that the pigeons were unable to survive without additional food provision.

Competition at feeding sites from non-native birds: Use of the feeding stations by other species has been noted. Madagascar turtle-doves Streptopelia picturata, common waxbills Estrilda astrild, house sparrows Passser domesticus, common mynahs Acridotheres tristis, and Madagascar fodies Foudia madagascariensis (all introduced species to Mauritius) have been seen to feed from the hoppers. Although this activity had little or no affect on the use of hoppers by pink pigeons, large quantities of supplementary food were consumed.

Competition at feeding sites between pink pigeons: Intraspecific competition occurred, with females often excluded from feeding at the hoppers by male courtship behaviour. Aggressive males often chased both females and other males from the feeding hoppers. However, due to there being two hoppers available, chased pigeons used the other hopper (positioned at least 5 m away), or returned later to feed undisturbed.

Conclusions: Seasonal shortages of natural food supplies have been suggested as limiting the wild population of pink pigeons, and from previous observations it seems likely that this has had a similar effect on the released population. As the reliance on supplemental feeding of most birds is apparent, its provision will be continued. From initial studies highlighting the benefits of supplementary food provision to released birds, regular supplementary feeding was extended to the wild subpopulation at Pigeon Wood.


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