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Aphids Find them How to ID Predators
"It has long been an axiom of mine that the little things are infinitely the most important" (Sherlock Holmes)

 

 

Identification & Distribution

The adult chiffchaff of the western subspecies (Phylloscopus collybita collybita, see first picture below) has brown-washed dull green upperparts, off-white underparts becoming yellowish on the flanks and a short whitish supercilium. Phylloscopus collybita collybita has dark brown to blackish legs (cf. willow warbler, which has paler pinkish-yellow legs), a fine dark bill (cf. willow warbler, which has a longer paler bill) and a short extension of flight feathers beyond the folded wing (cf. willow warbler, which has a longer extension of flight feathers beyond the folded wing). These features may seem clear enough, but can be difficult to see in the field. Fortunately their song and call are distinct. The song of the chiffchaff is a monotonous chiff-chaff (cf. the song of the willow warbler, which is a melodic rippling phrase with a descending trill at the end). The call of the chiffchaff is a monosyllabic 'hweet' (cf. the call of the willow warbler, which is a bisyllabic 'hu-eet' with the second syllable slurred upwards) (see also: chiffchaff versus willow warbler ).

First image Copyright Ken Billington under a Creative Commons Attribution-Share Alike 3.0 Unported License 
Second image Copyright Mike Pennington under a Creative Commons Attribution 2.0 Generic License 

Chiffchaffs feed on insects such as midges and other flies, aphids, caterpillars and moths, which they find by foraging in tree canopies and among bushes. We have termed it a generalized aphid predator but, when sufficiently large aphid populations are available, the chiffchaff probably comes closer than any other bird species to being a specific aphid predator.

There are three commonly accepted subspecies:

The western subspecies Phylloscopus collybita collybita is described above.
It breeds in Europe and winters around the Mediterranean and North Africa.
The north-western subspecies (Phylloscopus collybita abietinus) has a pale yellow supercilium and whitish underparts.
It occurs in Scandinavia and northern Russia, and winters from southeastern Europe and northeastern Africa to Iraq and Iran.
The Siberian chiffchaff (Phylloscopus collybita tristis, see second picture above) is duller in colour, with a longer supercilium than in the western subspecies.
It breeds in Siberia, and winters in the lower Himalayas and sometimes Western Europe.

 

Biological Control of Aphids

Birds in the genus Phylloscopus (meaning 'leaf explorer') are known as leaf warblers. Chiffchaffs are important aphid predators, searching the undersides of leaves for insects feeding on the plant 's sugary sap (= phloem feeders).

Predation of bird cherry-oat aphids

The bird cherry-oat aphid, Rhopalosiphum padi,  is a fairly common cereal pest which transmits several viruses, the most serious of which is barley yellow dwarf virus.

Over 25 years Glutz von Blotzheim (2004),  (2010),  conducted a very substantive study on bird species feeding on Rhopalosiphum padi on bird cherry (Prunus padus) bushes in autumn. In all he recorded 36 species of birds preying on the aphids. Chiffchaff and blackcap (Sylvia atricappilla) were the most numerous and most intensively-feeding aphid predators.

The bird cherry oat aphid (see picture above) is a host alternating species whose winter host is bird cherry. Its summer hosts are cereals and grasses. Very large numbers of these aphids can build up on bird cherry in spring to early summer prior to migration, and again in the autumn when these aphids return to their primary (winter) host.

Birds began feeding on these aphids at a very low level during the second half of August, intensified their attentions in mid-September and, for Chiffchaff, feeding reached its peak from 3 to 22 October. Feeding declined rapidly as soon as night temperature fell under 2°C in late October or at the beginning of November. In autumn 2003 Glutz von Blotzheim estimated the total harvest by all birds from only two bird cherry bushes at 1.5 to 3 million aphids.

Predation of woolly apple aphids

Africa Gomez of The Rattling Crow  spotted this chiffchaff in winter. Unlike many related species the chiffchaff is fully insectivorous, so it cannot turn to berries or garden bird feeders. Fortunately for the chiffchaff, many aphid species can be found on their host plants well into winter, and the picture below shows a chiffchaff searching for woolly apple aphids (Eriosoma lanigerum ).

Eriosoma lanigerum is an important economic pest of apple. It causes severe damage through direct feeding (especially to the roots, where it is hard to detect or control) rather than via virus transmission.

Image copyright Africa Gomez under a Creative Commons Attribution-Share Alike 3.0 Unported License 

A colony of woolly apple aphids can be seen in the photo above under the twig that the bird is standing on. A close-up of a colony of the same aphid is shown below.

One might expect that the abundant wax around woolly apple aphid colonies would make the aphid distasteful to predators, or at least serve to conceal them. Moss et al. (2006)  showed that wax is indeed hiding visual cues used for prey identification, at least in relation to spider predation. Nevertheless, the chiffchaff is not the only bird species reported as targeting the woolly apple aphid - Moeed, 1979  made similar observations on the silvereye, Zosterops lateralis, in New Zealand.

Predation of thistle aphids

In their natural history blog, Moorhen,  Roy & Marie Battell show this wonderful picture of a chiffchaff picking off black aphids from a thistle in June 2011.

 

Image reproduced by permission, copyrightMoorhen  all rights reserved

In this case these aphids are a subspecies of the common blackfly (Aphis fabae ) known as Aphis fabae cirsiiacanthoidis.

Aphis fabae cirsiiacanthoidis overwinter as eggs on spindle (Euonymus europaeus). In spring they hatch, and develop to winged forms which migrate to thistle, where they build up to large populations in summer.

Unlike Aphis fabae (which is a notorious and polyphagous pest), Aphis fabae cirsiiacanthoidis is seldom considered a problem, except perhaps for crops of globe artichoke (Cynara scolymus) in Western France (Robert & Le Gallicit, 1991 ).

Black is commonly regarded as an aposematic (warning) colour to predators, and blackfly usually are distasteful to vertebrate predators such as birds. However, for animals to learn that certain insects taste bad, they have to at least sample them - which may be what this chiffchaff is doing - unless, perhaps, chiffchaffs have evolved ways to cope with whatever is distasteful in Aphis fabae.

Predation of water lily aphids

We are grateful to Humano, Creativemente Humano,  for this photo of a chiffchaff hunting aphids on the flower pedicels of narrow-leaved water plantain (Alisma lanceolatum).

 

Image reproduced by permission, copyright David Yifrach, HCH,  all rights reserved.

The most likely prey in this case was the water lily aphid, Rhopalosiphum nymphaeae  (see picture below), which occurs on the leaves and petioles of water lilies and other aquatic plants.

Rhopalosiphum nymphaeae alternates between two hosts: in spring it feeds on Prunus species (including some fruit trees) where it causes some early leaf-curl. In early summer it moves to various water plants. In either case, it seldom causes serious damage.

Predation of mealy plum aphids

Bibby & Green (1983)  examined the feeding ecology of migrating warblers in French marshlands. Diet was assessed by analysis of faeces collected from the previously cleaned bags in which individual birds were kept before ringing. At Le Migron, aphids made up over 50% of the food items of the chiff chaff. Mealy plum aphids, Hyalopterus pruni  (see picture below), occurred densely on the leaves and panicles of reeds (the aphid's secondary host), and likely comprised most of the aphid component of the diet. Compared to other migrating warblers the chiffchaff ate fewer aphids than the sedge warbler, but similar numbers to willow warblers.

Hyalopterus pruni alternate between plum species and reeds / wetland grasses. It is considered a pest of plum, and (in America) may cause problems to one of its summer hosts Phragmites australis (the common reed).

Bibby & Green found an average of about 450 aphids per stem in early August, which fell exponentially to near zero by the end of the month. In another site (Passay), with no mealy plum aphids, flies made up most of the food items and no aphids were recorded.

It would appear therefore that chiffchaff may 'switch' to feeding on a particular aphid species when it becomes very common. The aphid Hyalopterus pruni displays red-green polymorphism when it is feeding on reeds. If birds feed on one morph more than the other, bird predation is likely to be one factor maintaining this polymorphism.

Other aphids predated by chiffchaffs

Laursen (1978)  compared the diet composition of six Phylloscopus and Sylvia species by examining stomach contents following use of a purgative. The study was done in Jutland, Denmark in spring (April and May) on birds migrating to their breeding areas in Scandinavia. The birds were caught with mist nets in an area where the vegetation consisted either of hawthorn-covered slopes, or on a plateau with birch, cherry, sitka spruce and elder. All bird species showed great flexibility, with regard to the different groups of prey, between successive periods within a migrating season - and from year to year. No aphids were identified in the diet of chiffchaffs (Phylloscopus collybita), but they mainly ate psyllids (closely related to aphids) or chironomids (non-biting midges), depending on availability.

The psyllids were not identified, but were most likely Cacopsylla species (see picture above) which can be abundant on hawthorn early in the year. The absence of aphids in the diet of chiffchaffs in this study was probably because it was early in the year - before any build up of aphid populations.

Lopez-Iborra et al. (2005)  looked at the diet of Phylloscopus collybita wintering in a wetland in south-east Spain. Diet composition was assessed by analysing the gizzard content of 17 individuals that died accidentally during a ringing study. The bulk of the diet was composed of midges (Chironomidae) which represented 95% of the prey. Analysis of prey taken in relation to availability revealed very strong prey selection, with chiffchaffs selecting aggregated and less mobile prey such as chironomids, and avoiding abundant but fast-escaping prey such as Brachycera flies. Aphids fell in the less mobile category, but were not especially common. They were found in 29% of the birds, but represented less than 1% of their prey.

Notice however, since aphids are small fragile soft-bodied insects, bird gut (or fecal) contents are liable to underestimate aphid consumption.

Other pictures of chiffchaff predating aphids include chiffchaff on fennel  - this chiffchaff is most likely feeding on the aphid Cavariella aegopodii,  which occurs commonly on fennel, rather than fennel seeds as suggested by the photographer.

There is also a wonderful picture of a chiffchaff eating aphids on chrysanthemum,  and another of a chiffchaff eating an aphid,  possibly Euceraphis betulae,  from a birch leaf.

Acknowledgements

We especially thank Africa Gomez (The Rattling Crow),  also Roy & Marie Battell (Moorhen),  and Humano, Creativemente Humano,  for permission to use their photographs. We also thank Middle Farm, East Sussex,  and Plumpton College  for their kind assistance, and permission to sample.

For bird identification we have used BTO Bird identification videos  for the key characteristics, together with the latest Wikipedia account for each species. For aphids we have made provisional identifications from photos of living specimens, along with host plant identity using 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

  • Bibby, C.J. & Green, R.E. (1983). Food and fattening of migrating warblers in some French marshlands. Ringing and Migration 4, 175-184.  Full text 

  • Glutz von Blotzheim, U.N. (2004). Die Bedeutung der Blattlaus Rhopalosiphum padi (L., 1758) und der Traubenkirsche Prunus padus L., 1753 für Vögel. Der Ornithologische Beobachter 101, 89–98. Full text 

  • Glutz von Blotzheim, U.N. (2010). Die Bedeutung der Traubenkirschen-Hafer-Blattlaus Rhopalosiphum padi (L., 1758) und der Traubenkirsche Prunus padus L., 1753 für Vögel. Anzeiger des Vereins Thüringer Ornithologen 7, 29-48. Full text 

  • Kristin, A. (1991). Feeding of some polyphagous songbirds on Syrphidae, Coccinellidae and aphids in beech-oak forests. pp. 183-186 in: Polgar, L. et al. (eds) Behaviour and Impact of Aphidophaga.  Full text 

  • Laursen, K. (1978). Interspecific relationships between some insectivorous passerine species, illustrated by their diet during spring migration. Ordis Scandinavica 9, 178-192. Full text 

  • Lopez-Iborra et al. (2005). Diet of Common Chiffchaffs Phylloscopus collybita wintering in a wetland in south-east Spain. Revista Catalana d'Ornitologia 21, 29-36. Full text 

  • Moeed, A. (1979). Foods of the silvereye (Zosterops lateralis; Aves) near Nelson, New Zealand. New Zealand Journal of Zoology 6, 475-479. Full text 

  • Moss, R. et al. (2006). Mask of wax: Secretions of wax conceal aphids from detection by spider’s eyes. New Zealand Journal of Zoology 33(3), 215-220. Full text 

  • Robert, Y. & Le Gallic, J.F. (1991). Two Important Host-plants for Black Aphids of the 'Aphis fabae Complex' in the West of France (Homoptera: Aphididae). Entomologia Generalis 16(4), 285-293. Abstract