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Generalized Aphid predator (Passeriformes : Parulidae)

Setophaga tigrina

Cape May Warbler

On this page: Identification & Distribution  Biological Control of Aphids:  Predation of currant aphids,  elm aphids  More on Cape May Warbler feeding behaviour 

Identification & Distribution

The adult Cape May warbler (Setophaga tigrina) has a short tail, a thin bill and white undertail coverts. The male (see first picture below) has a chestnut cheek patch, a dark crown and nape and a yellow collar. The yellow breast is marked with black streaks which continue down the flanks. The rump is bright yellow. The female Cape May warbler (see second picture below) has a grey cheek patch, an olive-gray crown and a somewhat paler yellow collar and breast. The breast is marked with paler dark streaks than the male. Immature Setophaga tigrina are generally dull gray, usually with a little yellow on the rump.

First image Copyright Andy Reago & Chrissy McClarren under a Creative Commons Attribution 2.0 Generic License 
Second image Copyright Philip R Brown under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License 

In its breeding grounds the Cape May warbler's preferred prey is spruce budworm (tortricid moths of the Choristoneura genus, including the pests Choristoneura fumiferana & Choristoneura freemani) but it feeds on other insects when migrating south. In the West Indies it also feeds on nectar with its curled, semitubular tongue. Setophaga tigrina breeds across the boreal forests of Canada and the northern United States. It migrates through central and southern United States to overwinter in the West Indies.

 

Biological Control of Aphids

When its preferred prey of spruce budworm is unavailable, there is considerable anecdotal evidence that the Cape May warbler is very partial to aphid colonies.

Predation of currant aphids

Cape May warblers migrate from their wintering areas to their breeding grounds in spring. The pictures below are from the Magee Marsh Wildlife Area, on the south shore of Lake Erie in the USA, during this spring migration. Birds tend to aggregate here as they wait for the right conditions to fly across Lake Erie as they migrate north.

One such Cape May Warbler was observed probing among the flowers (see picture below) of a currant bush branch. Close observation revealed the bird was meticulously gleaning aphids among the petioles and flowers.

Image reproduced by permission, Copyright Roads End Naturalist,  all rights reserved

The most likely aphids, in this case, are Hyperomyzus lactucae  (the blackcurrant-sowthistle aphid, see picture below). Hyperomyzus lactucae causes current leaf-crinkling (see above). It is widespread in temperate parts of the world, and is a major pest species of currants. The blackcurrant-sowthistle aphid also seems to be a favourite prey of other insectivorous birds, such as the American goldfinch. 

The Cape May warblers were also seen moving along the tree trunks, foraging for midges and other small insects from the bark furrows.

Predation of elm aphids

Greg Dodge, the park naturalist of the Museum of Life and Science  in North Carolina, USA, describes the vast numbers of flying insects seen in October in their six acre woodland and wetland site in his blog Nature Watch.  The swarms turned out to be winged aphids (see picture below) returning to their winter host - elm. They were in the Eriosomatinae subfamily and were most likely Eriosoma americanum, or possibly Colopha ulmicola.

Image reproduced by permission Copyright Museum of Life & Science,  all rights reserved

While watching the aphids Greg saw a small bird fly out from an elm branch at the edge of the Wetlands. There were four, maybe five of these birds working their way through the trees along the edge of the water, flying out from the branches, catching aphids. At least three of them were Cape May Warblers - one of which is shown below.

Image reproduced by permission Copyright Museum of Life & Science,  all rights reserved

These Cape May Warblers would have been migrating through North Carolina on their way to the West Indies where they overwinter.

 

More on Cape May Warbler feeding behaviour

Mark Trabue provides a fine close-up of a Cape May Warbler taking an aphid on a branch  as does Keara English - see Cape May Warbler with aphid. 

Cooper et al. (1997)  reviewed the feeding habits of the Cape May Warbler in British Columbia. They described the bird as a foraging generalist overall, but with seasonal specialisations. It mainly forages the canopy, eating a variety of small insects, as well as berries, seeds, tree sap, nectar and pollen. During the spring migration, nectar, pollen and tree sap are important food sources, but insect larvae are its primary food during the nesting season. It feeds mainly by gleaning prey from tree foliage primarily along branches rather than at the terminal tips. The population size of warblers expands rapidly during outbreaks of its main prey, in Eastern North America, spruce budworm (Choristoneura fumiferana).

Rogers et al. (1997)  provides a fascinating account of flower nectar feeding by Cape May, Tennessee and Nashville Warblers. All three species were observed nectar feeding from the flowers of wild plum trees in Minnesota, USA. The birds probed their bills deep into flower after flower as quickly as they could, moving from one cluster of flowers to another. Such behaviour may have been prompted by the cold spell of weather which suppressed insect activity.

Latta et al. (2003)  found that a honeydew-producing scale insect (Stigmacoccus garmilleri sp. ) was associated with the tree Bursera simaruba in subtropical dry forests in the Dominican Republic. At two study sites, 91% of Bursera trees supported locally dense populations of scale insects. Fifteen species of birds were observed foraging on the honeydew, with most observations made of the winter resident Cape May warbler (Setophaga tigrina) and three other species. The Cape May warbler actively defended the honeydew resource, but frequency of use of honeydew was influenced by the close presence of flowering agave and scale insect density. Honeydew may be a critical component of the diet of this species especially during the late winter dry season. Hymenoptera also were observed feeding on honeydew, but rates of consumption did not approach that of avian species. It is proposed that birds are able to maintain relationships with scale insects in moist, warm temperate forests because it is in these climates where ant abundance is low and reduced competition with ants allows bird use of honeydew.

Acknowledgements

We especially thank Mike Dunn (Roads End Naturalist)  and Greg Dodge,  the park naturalist of the Museum of Life & Science  for permission to use their photographs. We also thank Plumpton College  for their kind assistance, and permission to sample.

For bird identification we have used Cornell Lab of Ornithology   for the key characteristics, together with the latest Wikipedia account for each species.

For aphids we have made provisional identifications from high resolution photos of living specimens, along with host plant identity. We have used the keys and species accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Blackman (1974) , Stroyan (1977) , Stroyan (1984) , Blackman & Eastop (1984) , Heie (1980-1995) , Dixon & Thieme (2007)  and Blackman (2010) . We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure  provided by Blackman & Eastop (2006).

Useful weblinks 

References

  • Cooper, J.M. et al. (1997). Status of the Cape May warbler in British Columbia. Wildlife Working Report WR-82 Full text 

  • Latta, S.C. et al (2003). Revising the convergence hypothesis of avian use of honeydew: evidence from Dominican subtropical dry forest. Oikos 93(2), 250-259. Full text 

  • Rogers, L. (1997). Nectar feeding by Cape May, Tennessee and Nashville Warblers in Minnesota. Loon 69, 55-56. Full text