The diet of a pair of Northern Goshawks in the urban center of Berlin

Introduction

Berlin has an urban goshawk population of around 100 pairs (Kenntner, 2018). Such populations exist in several German cities, notably Hamburg and Cologne. Monitoring of the goshawk population in Hamburg suggests that the abundance of urban goshawks can be linked, among other factors, to the high availability of prey, particularly feral pigeons (Rutz, 2008). The observations annotated here confirm this, however, goshawk diet is not constrained to pigeons. Variations in diet include crows, small passerines and other raptors.

Data and Methods

The observations annotated here are the result of monitoring a couple of northern goshawks (Accipiter gentilis) nesting in a Berlin cemetery. The location of the cemetery has been obscured, to protect the birds from poachers. The area was visited 46 times from December 2017 until December 2018. The pair of goshawks occupied the area during all this time. Three chicks were raised, hatching in May and dispersing in August.

The pluckings were photographed in the nesting area. Plucking analysis is a standard method to obtain predation data for raptors, however it should be noted that plucking analysis can be biased by two factors: selective prey transportation by the predator and varying detectability of feathers of the prey species (Rutz, 2003).

The pictures were uploaded to iNaturalist and added to the "Found Feathers" group. For difficult identifications, the feathers were collected and kept as reference. This resulted in 38 "research grade" observations, i.e. the observation have correct metadata (date and coordinates), and the species id is reviewed by the online community.

Results

Table 1 shows the diet composition, in prey count and relative biomass. Biomass estimation was obtained from Dunning (2007), see additional material for details.

Table 1: Diet of a pair of Northern Goshawks in the urban center of Berlin.

Species N=38 N % Biomass %
Columba livia domestica 16 42.10 42.98
Columba palumbus 9 23.68 33.47
Corvus cornix 3 7.89 12.98
Turdus merula 2 5.26 1.71
Pica pica 2 5.26 3.13
Turdus philomelos 1 2.63 0.52
Fringilla montifringilla 1 2.63 0.18
Garrulus glandarius 1 2.63 1.19
Falco tinnunculus 1 2.63 1.40
Pyrrhula pyrrhula 1 2.63 0.17
Asio otus 1 2.63 2.27

Discussion

A comparison to previous work by Rutz (2003, 2006) in Hamburg found similarities and differences in diet, however feral pigeons clearly dominate the diet of northern goshawks in both urban areas. Columbidae are the most important prey group of goshawks in Berlin and in Hamburg, by number of prey items and by biomass. The second prey group are Corvidae. The diet of urban goshawks is however more diverse, as passerines the size of blackbirds or smaller, as well as diurnal and nocturnal raptors are also preyed upon.

Acknowledgements

The iNaturalist "group" feature, specifically the "found feathers" group, proved particularly helpful for identifying prey items. I wish to thank Amanda Janusz (@featherenthusiast) the founder of the "found feathers" group, as well as all iNaturalist contributors who identified these observations: @alexis_orion, @audun, @bluejay2007, @brennafarrell, @chwillbill68, @crapfou, @dendzo, @jakob, @karoopixie, @ldacosta, @martingrimm, @peterwijnsouw, @richardjaybee, @thekat, @tlaloc27, @solokultas, @stephen54

References

Dunning Jr, J. B. (2007). CRC handbook of avian body masses. CRC press.

Kenntner, N. (2018). Urbaner Habicht in Berlin, http://habicht-berlin.de/ (13 December 2018)

Rutz, C. (2003). Assessing the breeding season diet of goshawks Accipiter gentilis: biases of plucking analysis quantified by means of continuous radio-monitoring, 259, 209–217. https://doi.org/10.1017/S0952836902003175

Rutz, C. (2008). The Establishment of an Urban Bird Population. Source: Journal of Animal Ecology Journal of Animal Ecology, 77(77), 1008–1019. https://doi.org/10.1111/j.l365-2656.2008.01420.x

Additional material

Average biomass estimation, based on Dunning (2007), total biomass in goshawk diet (grams).

Species Average mass Total mass in diet
Columba livia 354 5664
Columba palumbus 490 4410
Turdus philomelos 68 68
Fringilla montifringilla 24 24
Corvus cornix 570 1710
Garrulus glandarius 157 157
Turdus merula 113 226
Pica pica 206 412
Falco tinnunculus 184 184
Pyrrhula pyrrhula 22 22
Asio otus 299 299
13176

Lähettänyt alvarosaurus alvarosaurus, 13. joulukuuta 2018 20:06

Havainnot

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Joulukuu 2017

Paikka

Germany (Google, OSM)

Kuvaus

I've been observing a goshawk for several weeks.

These are rests of a meal. By the shape of the feathers, these belonged to a pigeon.

Checked on Featherbase: https://www.featherbase.info/en/species/columba/livia

The white tag is 9 cm long

Merkinnät

Kuvat / Äänet

Mitä

Sarvipöllö (Asio otus)

Havainnoija

alvarosaurus

Päivämäärä

Joulukuu 2017

Paikka

Germany (Google, OSM)

Kuvaus

I've been observing a goshawk for several weeks.

These are rests of a meal. I first thought these were from a kestrel, but thanks to help from xeno-canto members Frank Holzapfel and Piotr Szczypinski these could be identified as feathers from a long-eared owl (Asio otus).

Checked on Featherbase: https://www.featherbase.info/en/species/Asio/otus

The ruler at the bottom is 50cm long

Merkinnät

Kuvat / Äänet

Mitä

Punatulkku (Pyrrhula pyrrhula)

Havainnoija

alvarosaurus

Päivämäärä

Joulukuu 2017

Paikka

Germany (Google, OSM)

Kuvaus

I've been observing a goshawk for several weeks.

These are rests of a meal. Found under the same tree as https://www.inaturalist.org/observations/9241283
The underside was ripped open, but the feathers were not plucked. I'm surprised a goshawk would eat prey this small, still, this tree is frequented by a goshawk and the base of this tree is littered with remains of prey. I heard a goshawk call at ca. 160m distance. I cannot rule out that the bird was killed by a cat or some other predator, but goshawks seem to catch prey smaller than a blackbird quite often (Rutz, 2003).

I also found pigeon (Columba livia) feathers under another tree at 100m distance.

Sorry for the gross image but this is interesting for reasons explained very well in the community guidelines: https://www.inaturalist.org/pages/community+guidelines

Rutz, C. (2003). Assessing the breeding season diet of goshawks Accipiter gentilis: biases of plucking analysis quantified by means of continuous radio-monitoring. Journal of Zoology, 259(2), 209-217.

Merkinnät

Kuvat / Äänet

Mitä

Sepelkyyhky (Columba palumbus)

Havainnoija

alvarosaurus

Päivämäärä

Helmikuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

I've been observing a pair of Goshawks for several months. These are the rests of a meal. I did not find the primaries, which are easy to identify. But I think the tail feathers are typical for wood pigeons (not sure). see: http://featherbase.info/en/species/columba/palumbus

Merkinnät

Kuvat / Äänet

Mitä

Harakka (Pica pica)

Havainnoija

alvarosaurus

Päivämäärä

Helmikuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

I've been observing a pair of goshawks for several months. These are rests of a meal.
see: http://featherbase.info/en/species/Pica/pica

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Tammikuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

I've been observing a pair of goshawks for several months. These are rests of a meal. see: http://featherbase.info/en/species/Columba/livia

Merkinnät

Kuvat / Äänet

Mitä

Sepelkyyhky (Columba palumbus)

Havainnoija

alvarosaurus

Päivämäärä

Tammikuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

I've been observing a pair of goshawks for several months. These are the rests of a meal. see: http://featherbase.info/en/species/columba/palumbus
(the primaries a dark with a distinctive white edge)

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Maaliskuu 2018

Paikka

Germany (Google, OSM)

Merkinnät

Kuvat / Äänet

Mitä

Varis (Corvus cornix)

Havainnoija

alvarosaurus

Päivämäärä

Toukokuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. The notebook is 14cm long.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Toukokuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Kesäkuu 2018

Paikka

Germany (Google, OSM)

Merkinnät

Kuvat / Äänet

Mitä

Mustarastas (Turdus merula)

Havainnoija

alvarosaurus

Päivämäärä

Kesäkuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. The notebook (pic.2) is 14 cm long. The down feathers (pic. 3) were darker than the remains of the carrion crow I found several weeks ago. Could this be another kind of crow or perhaps a blackbird?

Kuvat / Äänet

Mitä

Tuulihaukka (Falco tinnunculus)

Havainnoija

alvarosaurus

Päivämäärä

Kesäkuu 2018

Paikka

Germany (Google, OSM)

Kuvat / Äänet

Mitä

Varis (Corvus cornix)

Havainnoija

alvarosaurus

Päivämäärä

Kesäkuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. The notebook is 14 cm.

Kuvat / Äänet

Mitä

Harakka (Pica pica)

Havainnoija

alvarosaurus

Päivämäärä

Kesäkuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. The notebook is 14 cm. The feathers are glossy green-blue. Probably magpie covert feathers.

Kuvat / Äänet

Mitä

Mustarastas (Turdus merula)

Havainnoija

alvarosaurus

Päivämäärä

Heinäkuu 2, 2018 06:40 PM CEST

Kuvaus

Blackbird with head chopped off, uneaten. Found nesr goshawk nest. Untypical prey, too small. Cat?

Kuvat / Äänet

Mitä

Sepelkyyhky (Columba palumbus)

Havainnoija

alvarosaurus

Päivämäärä

Heinäkuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Found near goshawk nest.

Kuvat / Äänet

Mitä

Närhi (Garrulus glandarius)

Havainnoija

alvarosaurus

Päivämäärä

Heinäkuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Found near goshawk nest.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Heinäkuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawks prey. Found near where 3 goshawk juveniles where observed the day before.

Kuvat / Äänet

Mitä

Varis (Corvus cornix)

Havainnoija

alvarosaurus

Päivämäärä

Heinäkuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Found under abandoned nest. I had first filed these as jay feathers. @featherenthousiast identified these as leucistic hooded crow (thanks). I observed several flocks of crows and found that around 10% of crows are leucistic to some degree.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Elokuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey.

Kuvat / Äänet

Mitä

Sepelkyyhky (Columba palumbus)

Havainnoija

alvarosaurus

Päivämäärä

Elokuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Found under a tree where goshawks perch habitually. Beheaded but uneaten. This is the 3rd uneaten prey I've found since December in this area.

Kuvat / Äänet

Mitä

Sepelkyyhky (Columba palumbus)

Havainnoija

alvarosaurus

Päivämäärä

Elokuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Elokuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Sepelkyyhky (Columba palumbus)

Havainnoija

alvarosaurus

Päivämäärä

Elokuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Sepelkyyhky (Columba palumbus)

Havainnoija

alvarosaurus

Päivämäärä

Elokuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Syyskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Sepelkyyhky (Columba palumbus)

Havainnoija

alvarosaurus

Päivämäärä

Syyskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Syyskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Syyskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey

Kuvat / Äänet

Mitä

Peippo (Fringilla coelebs)

Havainnoija

alvarosaurus

Päivämäärä

Syyskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Small passerines are an untypical prey. Feathers found spread over 10m directly under this year's abandoned nest. The notebook is 15cm.

Kuvat / Äänet

Mitä

Laulurastas (Turdus philomelos)

Havainnoija

alvarosaurus

Päivämäärä

Lokakuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Found under a spruce with a goshawk nest from a previous year. Partially eaten.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Lokakuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey found under a tree often used for plucking.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Marraskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey found at usual plucking location. Goshawk seen. Female.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Marraskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Plucked on the ground. Found near this year's goshawk nest.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Marraskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Found directly under a habitual plucking perch.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Marraskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey. Found in an area where goshawks nested this spring.

Kuvat / Äänet

Mitä

Kesykyyhky (Columba livia var. domestica)

Havainnoija

alvarosaurus

Päivämäärä

Marraskuu 2018

Paikka

Germany (Google, OSM)

Kuvaus

Goshawk prey found under a limetree frequented by goshawks for plucking.

Kommentit

Wonderful entry! Great job. :)

Lähettänyt sambiology melkein 3 vuotta sitten (Lippu)

Do you have any pictures of the goshawks? I couldn't find any entries with pictures of them.

Lähettänyt vermfly melkein 3 vuotta sitten (Lippu)

Hi @vermfly,

I don't have a large enough telelens, goshawks generally won't let people come closer than 100m. But I have a picture made with the phone as a juvenile leaped out of the nest before he could fly and spent several days on the ground. https://www.inaturalist.org/observations/13617615

cheers

Lähettänyt alvarosaurus melkein 3 vuotta sitten (Lippu)

Wow, very interesting. Do you happen to know why goshawks started to live in urban area in Germany? Here in Canada, and I think most places in their range, goshawks are mostly only found in remote forests such as the boreal forest up north. Their relatives Cooper's Hawk and Sharp-shinned Hawk are common in cities though (I think Sparrowhawk is like that in Europe too?).

Lähettänyt upupa-epops melkein 3 vuotta sitten (Lippu)

Hi @upupa-epops,

goshawks started colonizing German cities in the mid-80's. Why this happened is difficult to explain, however there seems to be a decline in rural populations, so goshawks could be redistributing themselves. Once established in the city, they need to find sufficient food and a place to breed, so the factors enabling colonization and those enabling expansion may be different. Apparently, goshawks are doing well in the city, there have been reports that they have more parasites than their country cousins but they manage to breed very well.

I think Canadian goshawks are migratory? The German population seems to be quite sedentary, at least the urban ones.
As for urban sparrowhawks, these are typically found in garden plots, but are quite common too.

Lähettänyt alvarosaurus melkein 3 vuotta sitten (Lippu)

That's a lovely analysis of your iNat data, and a cool way to use iNat's journal as a scientific outlet. Way to go, @alvarosaurus!

Lähettänyt jakob melkein 3 vuotta sitten (Lippu)

Very interesting,thanks for info. :)

Lähettänyt stephen54 yli 1 vuosi sitten (Lippu)

I'm honored to help you out with this!

Lähettänyt bluejay2007 yli 1 vuosi sitten (Lippu)

Awesome! It's incredible to see the many practical applications of feather identification, especially as a tool to analyze the habits of these fascinating yet elusive raptors. I'm glad to have helped.

Lähettänyt featherenthusiast yli 1 vuosi sitten (Lippu)

Super data! I see you have tagged me as one who helped you identify. Twasn't me. You probably meant @karakaxa ?

Lähettänyt karoopixie yli 1 vuosi sitten (Lippu)

Nice! Thanks @karakaxa for the IDs :)

Lähettänyt twan3253 yli 1 vuosi sitten (Lippu)

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