What do Swifts Eat

2024

Bolus analysis

a bolus was dropped by an adult, retrived the following day and sent for analysis

Phoridae scuttle flies 28%

Scathophagidae dung-flies 23%

Chironomidae chironomids 12.4%

Tipulidae craneflies 7.4%

Cyclorrhapha circular-seamed flies No further classification 7.4%

Dolichopodidae 4%

Muscidae house flies 4%

Culicidae mosquitos .23%

Trichoceridae winter gnats .23%

Number of items 121

Droppings analysis

as in other years 20 random droppings were collected from below the nest boxes and sent away for analysis of contents

Scarabaeidae chafers 13.9%

Hemiptera true bugs No further classification 9.4%

Cyclorrhapha circular-seamed fly No further classification 9%

Aphidae aphids 8.9%

Scathophagidae dung-flies 8.2%

Cynapidae gall wasps 8.2%

wasps No further classification 7.3%

Coleoptera beetles No further classification 5.6%

Chironomidae non-biting midges 4.45%

Miridae capsid bugs 3.6%

Trichoptera (caddis flies) No further classification 3.6%

Ichneumonidae Ichneumons 3.6%

Pteromalidae Pteromid (parasitic) wasps 3.2%

Lonchopteridae spear-winged fly 2.5%
Muscidae house fly etc 2.5%

Tipulidae craneflies .7%
Diptera (S.O.Nematocera) No further classification .5%

Delphacidae plant hopper 2%
Phoridae scuttle bugs 1.5%
Cicadellidae plant hoppers 1.3%

Total number 584

Comments
Overall, diet composition this year was consistent with that in previous years at this site. As
before, the main prey groups were hemipteran bugs, cyclorraphan flies and wasps. These
three Orders, together with Coleoptera (most of which were small flying chafers (Serica spp)
made up just over 90% of the diet. The relative proportions of the four groups were more
even this year, with no group making up a huge proportion of the diet. As in past years, minor
components of the diet were nematoceran flies and other orders, in this case caddis flies.
While there were no real surprises in the results this year, four minor points could be
considered:
The proportion of beetles was higher than in 2023 and close to the value recorded in 2022
(20%). This is in keeping with known behaviour of small, flying chafers which hatch in large
“rises” periodically. This sample clearly coincided with a rise of Serica beetles, as in 2022.
The proportion of the diet made up of cyclorraphan flies (many of them dung flies) was much
the same as in previous years. However, as an aside, this year I noted that some of the faecal
pellets in the study contained large numbers of fly remains (two of them contained very little
else), while others contained none at all. This suggests that the flies were periodically available
in large numbers but that at other times the birds did not find any. This could be due to the very
changeable weather conditions prevailing in 2024. It also ties in with the results of the bolus
analysis (see separate report), which found that the bolus contained only flies – clearly collected
on a good “fly day”.
Recent media reports have suggested that weather conditions nationally this summer may have
been unfavourable for Hymenoptera as a group, since it appears there have been fewer social
wasps around than in a more “normal” summer. This is clearly not the case here, since the
proportion of Hymenoptera in the swifts’ diet is the highest yet recorded (22.4%). As before,
most species eaten were solitary wasps with a parasitic phase. Their ecology is therefore
different to that of social wasps.
As in previous years, the largest component of the birds’ diet was hemipteran bugs, including
aphids, which seem to have been as numerous as ever this year.