What Do Swifts Eat?

samples of swift chick droppings were collected at various sites across Northern Ireland between 2010 and 2025. My House, A Birch Hill Park, will be a permanent year on year study. Droppings in all cases were collected off the ground below nests when chicks were c3 weeks old and can poop out of nest sites. Droppings were dried and sent away for analaysis of insect contents. Bolus are sometimes found below nests.

No further classification, nfc, and eg mean the insect fragments couldnt be IDd to species

Swift site locations

A - collected at Birch Hill Park BT41 1DE

Country swifts living beside Lough Neagh – my house 1 mile / 1.6km from the shore of Lough Neagh.

with traces of
Hymenoptera - small solitary wasps
Coccinellidae - 11 spot ladybird

Birch Hill Park BT41 1DE 2021

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Birch Hill Park BT41 1DE 2022

Comments from the person doing the analysis
The main insect groups in the sample were like those in the 2019 and 2021 samples from the
same site although, as may be expected in a different summer, the relative proportions varied.
Noticeable changes were the increased proportion of Nematocera in the pellets this year. The
summer in the area having been less dry, the number of longhorn flies is likely to have been
higher than in 2021; in fact the numbers of longhorn fragments seems to have returned to a
level similar to that in 2019, i.e. to a more normal year. Cyclorrhaphan flies were also more
numerous in the diet in 2022, probably for similar reasons. The numbers of beetles were
similar to those in 2021; again, the main group was small chafers (Serica sp) which hatch in
large numbers from plants and get carried upwards on air currents. Their numbers were
broadly similar to those in 2021. It was noticeable that the numbers of hemipteran bugs were
down this year, mainly due to the drop in the proportion of aphids. Conditions may have been
less suitable for aphids, or it could be that there were fewer strong up currents taking them to
the height at which swifts forage. The reduction in the proportion of wasps may also have
been due to fewer strong up currents.
Overall, the diet of swifts at this site is pretty constant from year to year, and the proportions
of different groups was generally more similar this year to 2019 than to 2021. This is likely to
be due to weather conditions rather than to major changes in the insect population.

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Birch Hill Park BT41 1DE 2023

This year while collecting droppings part of a bolus was found

Cynapidae	gall wasps	19.7%
Aphidae	aphids	18.5%
Chironomidae	Lough Neagh flies	18.5%
Ichneumonida	ichneumon wasps	14.8%
Hemiptera	true bugs nfc	12.3%
Nematocera	midges, gnats nfc	7.4%
Cyclorrhapha	circular seamed fly	6%
Muscidae	house flies	2.5%

Comments
Clearly, on the day the bird collected this bolus, Nematocera were in abundance. This
analysis should be regarded as a snapshot of what a bird found to eat on one day, rather than a
detailed diet analysis. It further shows that swifts, like most animals, feed on what they can
get at the time.

Droppings results

Comments
As in previous years, the main prey groups from this site were hemipteran bugs, cyclorraphan
flies and wasps, and the relative proportions did not vary much between 2022 and 2023.
Again as last year, nematoceran flies made up a smaller proportion of the diet – 6.7% this
year. The proportion of beetles was down slightly – probably due to smaller rises of Serica
chafers this summer. A similar drop in chafer numbers was noted at the other site examined
this year – at CAFRE College. Wasp numbers were up on last year and are now more similar
to those recorded in 2019 and 2021. Also as at CAFRE College, lacewing remains were
recorded in the diet for the first time this year. Although the proportion was small, lacewings
are not numerous insects, and their inclusion at all is an indication of larger numbers of
lacewings in the area this year and/or strong upcurrents carrying them to greater heights.
Moths were recorded in very small numbers. This has been noted in previous years, and the
low proportion probably makes their inclusion of little importance to the swift population
locally.
As noted last year, the diet of the swifts at this site continues to be constant, taking into
account small variations due to weather conditions.

Birch Hill Park BT41 1DE 2024

Bolus analysis

Comments
It was notable that all the insects in the sample were flies and many of them dung flies, which
feed on animal dung. While individuals were not identified to species, many of the dung flies
were clearly the yellow dung fly (Scathophaga stercoraria) which feed in large numbers on
cattle dung. Scuttle flies (Phoridae) have larvae which feed in decaying organic matter and
are also common around cattle pastures. It is very likely, therefore, that the swift which
produced this bolus was feeding over cattle pasture. Given the relatively large numbers of
insects from a couple of families, this looks like opportunistic foraging on locally plentiful
insects.
This result differs from those of the faecal pellet analysis for the same period (see separate
report), which found fewer flies in the diet and as many bugs, beetles and wasps as in
previous summers. This difference emphasizes that the contents of a bolus will represent one
foraging period only, as opposed to feeding over several days. The contents of the bolus are

therefore likely to represent a relatively short foraging period and a more restricted location.

Droppings analysis

Scarabaeidae	chafers	13.9%
Hemipter	true bugs nfc	9.4%
Cyclorrhapha	circular-seamed fly	9%
Aphidae	aphids	8.9%
Scathophagidae	dungflies	8.2%
Cynapidae	gall wasps	8.2%
Hymenoptera	wasps nfc	7.3%
Coleoptera	water beetles nfc	5.6%
Chironomidae	Lough Neagh flies	4.45%
Miridae	capsid bugs	3.6%
Hymenoptera	caddisflies nfc	3.6%
Ichneumonidae	ichneumon wasps	3.6%
Pteromalidae	parasitic wasps	3.2%
Lonchopteridae	spear-winged flies	2.5%
Muscidae	house flies	2.5%
Delphacidae	plant hoppers	2%
Phoridae	scuttle bugs	1.5%
Cicadellidae	leaf hoppers	1.3%

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.

Birch Hill Park 2025 dropping analysis - 558 insect fragments

Cyclorrhapha	nfc	15%
Ichneumonidea	ichneumon wasps	11%
Hymenoptera	wasps nfc	10.7%
Hemiptera	true bugs nfc	10.7%
Chironomids	Lough Neagh flies	10%
Lonchopteridae	spear-wing flies	7%
Phoridae	scuttle flies	6%
Scarabaeidae	chafers	4.8%
Drosophilidae	fruit flies	4.6%
Miridae	capsid bugs	4.3%
Delphacidae	plant hoppers	3.7%
Coccinellidae	ladybirds	2%
Coleoptera	beetles	2%
Aphidae	aphids	2%
Nematocera	long-horn flies nfc	2.15%
Cynapidae	gall wasps	1.8%
Bibionidea	St Mark's flies	1.25%
Syrphidae	hoverflies	1.2%
Scathophagidae	dungflies	1%
Cicadellidae	leafhoppers	.9%
Pteromalidae	wasps	.9%
Muscidae	house flies etc	.7%
Dolichopodidae	long-legged flies	.5%
Tipulidae	craneflies	.35%

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, although 

this year there was a slightly increased proportion of nematoceran flies,

mainly chironomid  midges (warm summer). There were fewer beetles this year,

probably due to fewer large  rises of scarab chafers. Also, the inclusion in the diet of ladybirds (Coccinellidae) is new this  year. 

Birch Hill Park bolus 2025

Diptera	St Mark's flies	17%
Drosophilidae	fruit flies	17%
Phoridae	scuttle flies	16.4%
Cyclorrhapha	circular-seamed fly	16.4%
Chironomidae	Lough Neagh flies	15.4%
Nematocera	long-horned flies	15.4%
Pipunculidae	big-headed flies	10%
Syrphidae	hoverflies nfc	9.5%
Sepsidae	ensign flies	6.9%
Lauxaniidae	Lauxanid flies	4.2%
Lonchopteridae	spear-winged flies	4.2%
Aphidae	aphids	3.9%
Psilidae	rust flies	3.9%
Otidae?		3.3%
Muscidae	house flies	2.6%
Cicidellidae	leaf hoppers	2.3%
Ichneumonidae	ichneumon wasps	1.6%
Delphacidae	plant hoppers	1.6%
Scathophagidae	dungflies	1.3%
Hemerobiidae	brown lacewings	1.3%
Pipunculidae	big-headed fly	.9%

 

Comment 

The insect groups were similar to those in the diet analysis for the same site (above).  However, since the bolus is more of a

“snapshot” of one foraging session, the proportions of  each are somewhat different. Again, there were a lot of cyclorrhaphan

flies from a variety of  families, plus a relatively large percentage of non-biting midges (chironomids).  

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