Pukekura Park - its ecology and history - Friends of Pukekura Park New Plymouth Inc.


House Sparrows robbing Kowhai nectar

The earliest record I have found of the House Sparrow (Passer domesticus) feeding on the nectar of a native New Zealand plant is that of Stidolph (Emu 31 (1931): 7) who, in January 1928, saw that bird obtaining nectar from the flowers of Pohutukawa (Metrosideros excelsa) trees at Pukekura Park in New Plymouth.

 

McCann (Notornis 5 (1952): 8) observed that House Sparrows and Chaffinches (Fringilla coelebs) have devised a means of feeding on the nectar of the native New Zealand Kowhai (Sophora spp.). He said that they do this by nibbling a hole out of the calyx of the flower into the “cage” in which the nectar is imprisoned. The only record of House Sparrows feeding on Kowhai nectar in the definitive Handbook of Australian, New Zealand and Antarctic Birds 7B (2006) is that of Stidolph (in Notornis 21 (1974): 88) who mentioned that a group of House Sparrows fed on Kowhai nectar over several days by piercing holes in the base of the flower. An excellent photograph by Brian Chudleigh depicting a female House Sparrow nipping through the base of a Kowhai flower to reach the nectar within appeared in New Zealand Geographic No. 76 (2005). There are no records of Chaffinches feeding on Kowhai nectar in the Handbook. I have only once seen a Chaffinch feeding at Kowhai flowers like House Sparrows do, but Chaffinches may feed at Kowhai flowers more often than I have noticed.

 

Nectar robbers are birds, insects, or other flower visitors that remove nectar from flowers through a hole pierced or bitten in the corolla. They obtain a reward without contacting the anthers and stigma, thereby failing to effect pollen transfer. Charles Darwin assumed that nectar robbers had a negative impact on the plants that they visit, but research done in the last 50 or so years indicates that they often have a beneficial or neutral effect. Several studies document that robbers frequently pollinate the plants that they visit. Robbers may also have an indirect effect on the behaviour of the legitimate pollinators, and in some circumstances, the change in pollinator behaviour could result in improved plant fitness through increased pollen flow and outcrossing. The effects of nectar robbers are complex and depend, in part, on the identity of the robber, the identity of the legitimate pollinator, how much nectar the robbers remove, and the variety of floral resources available in the environment.

 

Mature Kowhai, nearly all Sophora microphylla, are common in Pukekura Park and Brooklands in central New Plymouth. They generally flower from early August until early October. I have seen House Sparrows, sometimes several in a tree at the same time,  feeding at those flowers on numerous occasions in recent years. House Sparrows undoubtedly rob nectar from them. I am not aware of any studies of the effects of this nectar robbing on the reproductive success of Kowhai. However, it seems unlikely that such behaviour, particularly where it occurs in the presence of legitimate pollinators such as the Tui (Prosthemadera novaeseelandiae), would have a significant detrimental effect on the reproductive success of that plant.

 

David Medway

 

Reproduced, with permission, from Miranda Naturalists’ Trust News No. 69 (April 2008) 

 


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