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Insectivorous birds consume an estimated 400–500 million tons of prey annually


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In this paper, we present an estimate of the predation impact of the global population of insectivorous birds based on 103 (for the most part) published studies of prey consumption (kg ha⁻¹ season⁻¹) of insectivorous birds in seven biome types. By extrapolation—taking into account the global land cover of the various biomes—an estimate of the annual prey consumption of the world’s insectivorous birds was obtained. We estimate the prey biomass consumed by the world’s insectivorous birds to be somewhere between 400 and 500 million metric tons year⁻¹, but most likely at the lower end of this range (corresponding to an energy consumption of ≈ 2.7 × 10¹⁸ J year⁻¹ or ≈ 0.15% of the global terrestrial net primary production). Birds in forests account for > 70% of the global annual prey consumption of insectivorous birds (≥ 300 million tons year⁻¹), whereas birds in other biomes (savannas and grasslands, croplands, deserts, and Arctic tundra) are less significant contributors (≥ 100 million tons year⁻¹). Especially during the breeding season, when adult birds feed their nestlings protein-rich prey, large numbers of herbivorous insects (i.e., primarily in the orders Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, and Orthoptera) supplemented by spiders are captured. The estimates presented in this paper emphasize the ecological and economic importance of insectivorous birds in suppressing potentially harmful insect pests on a global scale—especially in forested areas. Electronic supplementary material The online version of this article (10.1007/s00114-018-1571-z) contains supplementary material, which is available to authorized users.
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Martin Nyffeler
&Çağan H. Şekercioğlu
&Christopher J. Whelan
Received: 3 April 2018 /Revised: 8 June 2018 /A ccepted: 11 June 2018 / Published online: 9 July 2018
In this paper, we present an estimate of the predation impact of the global population of insectivorous birds based on 103 (for the
most part) published studies of prey consumption (kg ha
) of insectivorous birds in seven biome types. By extrapo-
lationtaking into account the global land cover of the various biomesan estimate of the annual prey consumption of the
worlds insectivorous birds was obtained. We estimate the prey biomass consumed by the worlds insectivorous birds to be
somewhere between 400 and 500 million metric tons year
, but most likely at the lower end of this range (corresponding to an
energy consumption of 2.7 × 10
or 0.15% of the global terrestrial net primary production). Birds in forests account
for > 70% of the global annual prey consumption of insectivorous birds (300 million tons year
), whereas birds in other
biomes (savannas and grasslands, croplands, deserts, and Arctic tundra) are less significant contributors (100 mil-
lion tons year
). Especially during the breeding season, when adult birds feed their nestlings protein-rich prey, large numbers
of herbivorous insects (i.e., primarily in the orders Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, and Orthoptera)
supplemented by spiders are captured. The estimates presented in this paper emphasize the ecological and economic importance
of insectivorous birds in suppressing potentially harmful insect pests on a global scaleespecially in forested areas.
Keywords Arthropods .Avifauna .Breeding season .Global impact .Insect pests .Predation
Birds, represented by nearly 10,700 species, are found across
the world in all major terrestrial biomes. Accordingly, they
exhibit a large variety of life styles and foraging behaviors
(see Wiens 1989). While some birds depend predominantly
on plant diets, such as seeds, fruits, and nectar, others feed as
carnivores on animal prey, or as omnivores on a mixed diet of
plant/animal matter. Most bird species are insectivores that
depend for the most part on insects as prey (Losey and
Vaughan 2006;Şekercioğlu 2006a). In this paper,
Binsectivorous birds^are defined in a wider sense as the total
of all bird groups that include, at least temporarily, a consid-
erable percentage of arthropods (in particular insects and spi-
ders) in their diets (Lopes et al. 2016). Included in this defini-
tion are also omnivorous birds such as starlings (Sturnidae)
and thrushes (Turdidae) that consume large amounts of arthro-
pods in additionto other types of food (Del Hoyo et al. 2016).
The predominance of insectivory as a feeding style among
birds might be explained by the fact that insects (dominating
the land biota in terms of numbers, biomass, and diversity)
constitute the largest food base for terrestrial carnivorous an-
imals. So, for instance, social insects alone are assumed to
have a standing biomass of > 700 million tons globally
(compare Hölldobler and Wilson 1994;Sanderson1996).
Şekercioğlu (2006b) states that birds are Bimportant but
ecologically little known actors in many ecosystems.^
Communicated by: Sven Thatje
Electronic supplementary material The online version of this article
( contains supplementary
material, which is available to authorized users.
*Martin Nyffeler
Section of Conservation Biology, Department of Environmental
Sciences, University of Basel, CH-4056 Basel, Switzerland
Department of Biology, University of Utah, Salt Lake
College of Sciences, Koç University, Rumelifeneri, Istanbul, Sariyer,
Department of Biological Sciences, University of Illinois at Chicago,
Chicago, IL 60607, USA
The Science of Nature (2018) 105: 47
The Author(s) 2018
Insectivorous birds consume an estimated 400500 million tons
of prey annually
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Likewise, Wenny et al. (2011)stateBBirds provide many eco-
system services, which by and large are invisible and
underappreciated.^It has thus been suggested that
Bquantifying the services provided by birds is crucial to un-
derstand their importance for ecosystems and for the people
that benefit from them^(Whelan et al. 2015). While several
attempts had been undertaken to quantify the food consump-
tion of marine birds and shorebirds on a global scale (e.g.,
Wiens 1989;Brooke2004), the combined predation impact
of the worlds insectivorous birds is still unknown.
Here, we provide estimates for the annual biomass of
prey that is consumed by the global population of insectiv-
orous birds in individual biome types and worldwide based
on data from the literature. Furthermore, we present an
estimate of the standing biomass of the global population
of insectivorous birds. This study is intended as a
continuation of the papers by Nyffeler (2000)and
Nyffeler and Birkhofer (2017)who were studying spi-
dersto get a better understanding of the global extent to
which potentially harmful herbivorous insects are sup-
pressed by major natural enemies.
Estimate of the standing biomass of the global
population of insectivorous birds
For each of seven terrestrial biome types, the bird biomass
across the entire biome was assessed by calculating the prod-
uct of (D)×(W)×(Y), whereby D= mean bird density
),W= mean bird b ody mass (kg fresh w eight bird
and Y= area size of the entire biome type (ha). The mean
breeding bird densities (representing global averages) for the
various biome types were extracted from a world literature
review by Gaston et al. (2003) and are largely in agreement
with North American breeding bird densities compiled by
Terborgh (1989, page 71). Area sizes for the various biomes
were taken from Saugier et al. (2001); essentially, these values
do not differ very much from the more up to date 2010 land
cover distribution data provided by FAO (https:// but are more suitable for our
purposes because they are broken down into more detailed
cover classes than the latter ones allowing a more rigorous
assessment. To obtain a mean body mass for Arctic tundra
birds, an overall mean for 18 tundra-inhabiting species (see
Sokolov et al. 2012) was calculated based on data from Del
Hoyo et al. (2016). An overall mean body mass for desert
birds was calculated based on weight data for 26 species oc-
curring in Chihuahuan deserts (Gutzwiller and Barrow 2002).
Mean bird body mass values for the remaining six biome
types were gathered from the following literature sources:
Howell (1971); Karr (1971); Wiens (1973); Holmes and
Sturges (1975); Wiens and Nussbaum (1975); Kartanas
(1989); and Terborgh et al. (1990).
Summing up the seven subtotals produced an estimate
of the standing biomass of the global terrestrial avifauna.
From this, an estimate of the standing biomass of the glob-
al population of insectivorous birds was deduced, assum-
ing that 90% of the terrestrial bird individuals in the
temperate, boreal, and arctic zones and 60% in the tro-
pics are arthropod-eaters (see Assumption 1, BMethods^
Estimate of the annual prey consumption
of the global population of insectivorous birds
We used a simple model involving few assumptions as is
advised in cases where a field of study is still largely un-
developed (Weathers 1983; Nyffeler and Birkhofer 2017).
Our estimate is based on mean values of prey consump-
tion ha
in the various biome types, which subse-
quently were extrapolated on a global scale. To retrieve
comparable data, all values obtained from the literature
were converted to kg fresh weight ha
. A total of
different information sources:
Source 1: In 26 cases, published values of prey consump-
tion were used (see Supplementary material).
Source 2: In 53 cases, energy demand estimates for bird
communities extracted from the scientific literature (see
Supplementary material) were converted into food con-
sumption measures. The conversions are based on an
overall average water content of arthropod prey of
70% (Zandt 1997; Brodmann and Reyer 1999;Bureš
and Weidinger 2000), an energy density of animal matter
of 22.5 kJ g
dry weight (Schaefer 1990), and 75% as-
similation efficiency (Wiens 1989). For details see
Supplementary material.
Source 3: There is a lack of data regarding the food
consumption rates of bird communities in desert and
Arctic tundra biomes. We thus calculated food con-
sumption rates for bird communities in these two bi-
ome types based on estimates of daily energy expen-
diture and breeding bird densities. Energy expended
for standard metabolism (M, in kcal day
lated with the equation M= 129 W
of Lasiewski
and Dawson (1967), whereby Wequals the weight of
an average sized bird in kg. Energy expended under
field conditions equals approximately 2.5 times stan-
dard metabolism (Holmes and Sturges 1975). For the
calculation of the desert biome values, cactus wren
(Campylorhynchus brunneicapillus, average body
mass = 38.9 g; Dunning 2007) was chosen as a stan-
dard bird representing this biome type, assuming a
47 Page 2 of 13 Sci Nat (2018) 105: 47
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breedingseasonlengthof90180 days (mean =
135 days) for deserts (Wiens 1991). In the case of the
Arctic tundra biome, snow bunting (Plectrophenax
nivalis, average body mass = 42.2 g; Dunning 2007)
was used as a standard tundra bird, whereby a breeding
season length of 100daysfortheArctictundrabi-
ome was assumed (Weiner and Głowaciński 1975). By
multiplying the resulting energy consumption value
for a standard bird with corresponding breeding den-
sity values taken from the literature (deserts: Austin
1970; Arctic tundra: Watson 1963; James and
Rathbun 1981; Montgomerie et al. 1983; Sokolov et
al. 2012), rough estimates of the energy consumption
for desert and Arctic tundra bird communities, respec-
tively, during the breeding season were obtained.
Subsequently, these energy consumption values were
converted into food consumption rates (the same conver-
sion factors being applied as in the previous paragraph),
which yielded 18 values fordesert and 6 valuesfor Arctic
tundra sites. For details see Supplementary material.
The 103 prey consumption values were assigned to the
following seven groups of terrestrial biomes: (1) tropical
forests, (2) temperate and boreal forests, (3) tropical
grasslands and savannas/Mediterranean shrubland, (4)
temperate grasslands (incl. meadows, pastures, old fields),
(5) cropland, (6) deserts, and (7) Arctic tundra. The data
were pooled by computing an average prey consumption
value (x
̅kg ha
) for each biome type. By multi-
plying the average prey consumption ha
with the
corresponding area size of each biome type (based on
Saugier et al. 2001), a prey consumption subtotal for each
biome type was derived. Summing up the seven subtotals
produced an estimate of the global annual prey consump-
tion by the insectivorous avifauna (Table 2). This figure
refers exclusively to arthropod prey, whereas other types
of invertebrates, such as earthworms, slugs, and snails, are
not included.
Our assessment is based on the following assumptions:
Assumption 1: Prey consumption measures presented
in the literature for land bird communities were
downsized to the corresponding values for insectivo-
rous birds, taking into account that an estimated 90%
of all land bird individuals (and about two thirds of
all species) in the temperate, boreal, and arctic zones
are insectivores during the breeding season, whereas
60% of all individuals (and 62% of all species) in
the tropics are insectivores. The figure of 60% has
also been chosen for non-tropical desert habitats
(see Supplementary material). The figure of 90% for
the Palearctic birds has been calculated based on pop-
ulation size/diet composition data for 422 bird species
presented in the data base BBirds of Switzerland^of
the Swiss Ornithological Institute Sempach; it can be
considered to be representative for the European
temperate/cold regions (see http://www.vogelwarte.
ch/en/birds/birds-of-switzerland/). A similarly high
proportion of all breeding land bird individuals in
the Nearctic realm are insectivores (calculated based
on data presented by Wiens 1973;Wiensand
Nussbaum 1975,Holmesetal.1986; and others).
Thefigureof60% for tropical birds is a rough es-
timate based on various sources (see Karr 1971,1975;
Poulin et al. 1994; Poulin and Lefebvre 1996;Leigh
1999;Sakai2002; Tscharntke et al. 2008; Maas et al.
2015; Sam et al. 2017).
Assumption 2: The breeding season diets of the avi-
fauna in temperate forests and in some temperate
grasslands are composed of 75% arthropods
(Głowaciński et al. 1984) and those in agricultural
areas of 95% arthropods (Jenny 1990;Jeromin
2002;Gilroyetal.2009). The diets of desert birds
are made up, on average, of 85% arthropods (e.g.,
Beal 1907). Accordingly, the food consumption
values for insectivorous birds of these biomes were
multiplied by a factor of 0.75, 0.95, and 0.85, respec-
tively, to obtain arthropod consumption measures
(kg fresh weight ha
). See Supplementary
material for exceptions.
Assumption 3: The arthropod consumption measures
for tropical biomes relate to annual totals (breeding
season plus non-breeding season; see Karr (1975);
Leigh and Smythe (1978); Reagan and Waide
(1996); Robinson et al. (2000); Sakai (2002)). By
contrast, the arthropod consumption values for tem-
perate biomes available in the literature in most cases
constitute exclusively breeding season values. The
majority of birds in temperate forests, grasslands,
and croplands as well as deserts and Arctic tundra
sites are primarily dependent on arthropod prey while
feeding their young during the breeding season (see
Wiens 1973,1977;Jenny1990; Buckingham et al.
1999;Jeromin2002; Gilroy et al. 2009). Once the
breeding season is over, many insectivorous birds
leave their temperate/cold zone breeding sites to mi-
grate to warmer areas, resulting in strongly reduced
bird densities in the breeding habitats during the non-
breeding season (Holmes and Sturges 1975;Karr
1975; Marone 1992; Scebba 2001).Atthesametime,
the vast majority of non-migratory residents, which
inhabit temperate/cold zone habitats, switch to a diet
made up largely of plant matter during the non-
breeding season (Clements and Shelford 1939;
Brown et al. 1979; Robinson and Sutherland 1997;
Buckingham et al. 1999; Renner et al. 2012).
Sci Nat (2018) 105: 47 Page 3 of 13 47
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Reduced arthropod consumption by non-migratory
birds might be explained by the reduced availability
of arthropod prey during the non-breeding season and
by the fact that vast regions located in temperate,
boreal, and polar climates are covered with a blanket
of snow for several months, making foraging for ar-
thropod prey difficult at this time. Notwithstanding
that, arthropod consumption in these biomes during
the non-breeding season continues to a limited extent
(Bruns 1960;Davies1976; Williams and Batzli 1979;
Heinrich and Bell 1995;Kirketal.1996; Michalek
and Krištín 2009;Velký et al. 2011). We assume that
in vast areas of the temperate and cold regions, the
arthropod consumption ha
during the entire non-
breeding season is 510% of the breeding season
value (see Holmes and Sturges 1973,1975;
Rotenberry 1980a,b;Donaldetal.2001). Therefore,
we multiplied the breeding season values for temper-
ate biomes and deserts by 0.075 to obtain the corre-
sponding non-breeding season values.
Assumption 4: Mediterranean shrublands were classi-
fied under Btropical savannas and grasslands^because
net primary production and bird densities in these two
habitat types are similar (Gaston et al. 2003;Chapinet
al. 2011). It must be added that the area size of
Mediterranean shrublands is small (280 × 10
ha) rel-
ative to the global terrestrial area, and a possible error
resulting from insufficient data is likely minor.
Assumption5: The estimates presented in this paper are
based on studies mostly conducted in the last three
decades of the twentieth century. Patterns of bird pop-
ulation decline as discussed more recently
(Şekercioğlu et al. 2002,2004) have not been taken
into account in the estimates presented here (Tables 1
and 2) because this would have exceeded the scope of
this paper owing to few estimates of bird population
declines in the twenty-first century.
Statistical analysis of annual prey consumption
in the various biomes
To determine whether prey consumption rates (kg arthro-
pods ha
) differed among biomes, we first deter-
mined that the consumption data among biomes were not
normally distributed using normal probability plots. Rather
than using a normalizing transformation, we instead per-
formed a Kruskal-Wallis one-way analysis of variance by
ranks test. The omnibus test was followed with a pairwise
multiple comparison using Dunns test for multiple com-
parisons of independent samples corrected for ties (Pohlert
2018). Analyses were performed with R, the programming
language (R Core Team 2018).
Standing biomass of the global population
of insectivorous birds
Based on estimates of avian standing biomass in various
terrestrial biomes, we estimate the total standing biomass
of the global terrestrial avifauna to be 3981 × 10
kg fresh
weight (= roughly 4 million metric tons; Table 1). This
value is similar to an estimate of 5 million tons for the
global terrestrial avifauna calculated using a different ap-
proach by Alerstam (1993). Because it is assumed that
90% of all land bird individuals in the temperate, boreal,
and arctic zones and 60% in the tropics are insectivorous
foragers (see Assumption 1, BMethods^section), it follows
that the standing biomass of the global community of in-
sectivorous birds might be on the order of 3 million tons
(Table 1). This value is a small fraction of the global stand-
ing biomass of other predaceous animal taxa such as spi-
ders (25 million tons; Nyffeler and Birkhofer 2017), ants
(280 million tons; Hölldobler and Wilson 1994), or
whales (16103 million tons; Pershing et al. 2010). The
comparatively low value of the global standing biomass
of wild birds is partially explained by the fact that birds
have a very low production efficiency (i.e., low P/A-ratio).
With other words, in birds, the vast majority of the assim-
ilated energy is lost in respiration and only 12% is con-
verted to biomass (see Golley 1968;HolmesandSturges
1975; Humphreys 1979).
Prey consumption rates of insectivorous birds
in the various biomes
Prey consumption rates (kg arthropods ha
significantly among biomes (Kruskal-Wallis chi-squared =
51.179, df = 6, P< 0.001; Fig. 1). A Dunnsposthocmul-
tiple comparison test revealed that prey consumption in
tropical forests was greater than in all other biomes (all
P0.022). Prey consumption in temperate-boreal forests
was greater than in tundra (P< 0.001), desert (P<0.001),
and temperate grasslands (P= 0.009), but did not differ
from tropical grasslands and croplands. Prey consumption
was greater in tropical grassland and savanna than in desert
(P= 0.004) and tundra (P= 0.024). Finally, prey consump-
tion was greater in cropland than in desert (P= 0.044).
Prey consumption did not differ significantly among any
of the remaining biomes. Annual prey consumption corre-
lated positively with net primary production among bi-
omes, using NPP values from Chapin et al. (2011).
47 Page 4 of 13 Sci Nat (2018) 105: 47
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Table 2 Estimated annual consumption of arthropod prey (fresh
weight) of the global population of insectivorous birds. Values for
temperate biomes refer to residents and breeding migrants combined;
values for tropical biomes refer to residents and non-breeding migrants
combined. Not included in these calculations are the amounts of arthro-
pod prey consumed at migration stopover sites
Biome class Number of
Prey consumption
(kg ha
Area (ha) Prey consumption of
entire area (kg year
Tropical forests
7 112.5 ± 9.2 1750 × 10
196,875 × 10
Temperate and boreal forests
44 44.1 ± 6.2 2410 × 10
106,281 × 10
Tropical grasslands and savannas/Mediterranean shrubland
7 15.8 ± 2.8 3040 × 10
48,032 × 10
Temperate grasslands (incl. meadows, pastures, old fields)
11 7.5 ± 0.9 1500 × 10
11,250 × 10
8 20.9 ± 9.0 1350 × 10
28,215 × 10
18 4.1 ± 0.8 2770 × 10
11,357 × 10
Arctic tundra
8 4.6 ± 1.3 560 × 10
2576 × 10
Global total (without ice-covered area) 103 13,380 × 10
404,586 × 10
Karr (1975); Leigh and Smythe (1978); Reagan and Waide (1996); Robinson et al. (2000); Sakai (2002)
Tima (1957); Uramoto (1961); West and DeWolfe (1974); Holmes and Sturges (1975); Karr (1975); Alatalo (1978); Szaro and Balda (1979); Smith and
MacMahon (1981); Wiens (1989) (modified data from Wiens and Nussbaum 1975); Wiens (1989) (modified data from Weiner and Głowaciński 1975;
Głowaciński and Weiner 1980,1983); Weathers (1983); Keast et al. (1985); Solonen (1986); Kartanas (1989); Harris (1991)
Karr (1971); UNESCO (1979); Gillon et al. (1983)
Diehl (1971); Wiens (1977); Rotenberry (1980b); Smith and MacMahon (1981); Głowacińskietal.(1984); combined data Faanes (1982)/Kirk et al.
Wiens and Dyer (1975); Woronecki and Dolbeer (1980); Kartanas (1989); Ferger et al. (2013)
Combined data Lasiewski and Dawson (1967)/Austin (1970)
Wielgolaski (1975); combined data Lasiewski and Dawson (1967)/Watson (1963); James and Rathbun (1981); Montgomerie et al. (1983); Sokolov et
al. (2012)
Values of prey kill (kg ha
) presented as x
Table 1 Estimated standing biomass of the global terrestrial avifauna
(expressed as fresh weight kg). Values of mean number of birds ha
in the various biome classes taken from Gaston et al. (2003), areas of the
various biome classes (Y) based on Saugier et al. (2001). Assuming that
90% of the terrestrial bird individuals in the temperate, boreal, and arctic
zones and 60% in the tropics are arthropod-eaters (see Assumption 1,
BMethods^section), it is deduced that the biomass of the worldsinsec-
tivorous birds might be 3 million tons
Biome class Mean density
(birds ha
Mean body weight
(kg bird
Area (ha)
Biomass across
biome (kg)
Tropical forests 20.00 0.0320
1750 × 10
1120 × 10
Temperate and boreal forests 10.00 0.0270
2410 × 10
651 × 10
Tropical grasslands and savannas/Mediterranean shrubland 9.25 0.0340
3040 × 10
956 × 10
Temperate grasslands 4.00 0.0450
1500 × 10
270 × 10
Cropland 3.00 0.0380
1350 × 10
154 × 10
Deserts 1.75 0.1558
2770 × 10
755 × 10
Arctic tundra 2.00 0.0674
560 × 10
75 × 10
Global total (without ice-covered area) –– 13,380 × 10
3981 × 10
Terborgh et al. 1990
Holmes and Sturges 1975; Wiens and Nussbaum 1975
Howell 1971;Karr1971
Wiens 1973
Kartanas 1989
Gutzwiller and Barrow 2002
Sokolov et al. 2012; Del Hoyo et al. 2016
Sci Nat (2018) 105: 47 Page 5 of 13 47
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Estimate of the global annual prey consumption
by the insectivorous birds
Our calculation of the annual prey consumption by the global
population of insectivorous birds produced an estimate of
404,586 × 10
kg year
(= 404.6 million tons; Table 2),
which corresponds to an energy consumption of 2.7 ×
(= 0.15% of the global terrestrial net primary
production of 1.782 × 10
(see Lieth 1973)).
This estimate (Table 2) does not include the amounts of
food consumed at stopover sites during the fall and spring
migrations. Currently, no quantitative assessments of the prey
biomass consumed at stopover sites have been published (also
see Lott et al. 2006); but considering the energy costs of ap-
proximately 10 to 20 billion birds migrating annually (see
Hahn et al. 2009; Berthold 2001;Wikelskietal.2003;
Fristoe 2015) and taking into account that the birds resting at
stopover sites only partially depend on arthropod food
(Schaub and Jenni 2000; Suthers et al. 2000), we estimate that
the amount of arthropod food they consume globally at stop-
over sites may be on the order of 35 million tons year
Thus, arthropod consumption during migratory stopovers is
around 1% of the total amount of prey biomass consumed by
the global population of insectivorous birds (see Table 2).
Regarding the temperate, sub-polar, and polar climates, our
calculations (Table 2) assume that the arthropod consumption in
these climates during the non-breeding season is reduced to a
small fraction (510%) of the breeding season value (see
BMethods^). However, there are some studies which indicate
that the insectivorous activities of birds during the non-
breeding season may not always be reduced so drasticallyat
least in some parts of the temperate/cold climate zones (see
Askenmo et al. 1977; Gunnarsson 1996; Kirk et al. 1996;
Velký et al. 2011)and it could therefore be argued our cal-
culations underestimate the contribution of birds as consumers
of arthropod prey during the non-breeding period (Table 2). To
address this issue, we considered two extreme scenarios. In sce-
nario 1, a minimum estimate was assessed based on the assump-
tion that the birdsdiets in temperate/cold climates contain no
arthropods during the non-breeding season; in scenario 2, a max-
imum estimate was assessed by assuming that the birdscontri-
bution as arthropod consumers during the non-breeding season
in temperate/cold climates is 50% of the breeding season value.
With these assumptions, the annual prey consumption of the
worlds insectivorous birds was recalculated, producing a mini-
mum estimate of 396,041 million tons year
and a maximum
estimate of 472,145 million tons year
. Thus, the true value of
insect consumption presumably is somewhere in between ap-
proximately 400 and 500 million tons year
at the lower end of this range as indicated in Table 2, because the
availability of arthropod prey during the non-breeding season is
greatly reduced in most areas of the temperate/cold climates.
For comparison, Alerstam (1993), using a different method,
estimated the total energy consumption of the worldslandbirds
(including arthropods, plant matter, and other food sources) to
be 7.5 × 10
. Our estimate for the worlds insectivo-
rous birds is consistent with this broader estimate. The difference
of 4.6 × 10
between the two estimates is mainly ex-
plained by the fact that in our estimate exclusively feeding on
arthropod prey is considered, whereas in Alerstams estimate,
feeding on additional food sources was assumed. Especially
during the non-breeding season, when the availability of arthro-
pod prey is strongly reduced in many places of the globe, land
birds consume large amounts of plant matter (Clements and
Shelford 1939; Brown et al. 1979; Robinson and Sutherland
1997; Buckingham et al. 1999;Renneretal.2012).
Experimental evidence supporting our theory of high
global predation impact by insectivorous birds
Our calculations presented in Table 2imply that insectivorous
birds exert substantial predation pressure on insects and other
arthropods, especially in tropical and temperate/boreal forest
ecosystems. This is supported by a large number of experi-
mental studies conducted in a variety of habitats in different
parts of the world (see Şekercioğlu 2006a, Mäntylä et al. 2011;
Şekercioğlu et al. 2016 for reviews). Thereby, exclosure ex-
periments were used to document the impact of bird predation
Fig. 1 Box plots showing prey consumption rates
(kg arthropods ha
) in the various biomes. Different small case
letters above boxes indicate significant differences (Kruskal-Wallis test
followed by Dunns multiple comparison test; see text for details). High
and low whiskers indicate 90th and 10th percentiles, respectively. Tops
and bottoms of the boxes indicate 75th and 25th percentiles, respectively.
The horizontal bars withinthe boxes indicate the median, and the symbols
within the boxes indicate the mean biomass consumed
47 Page 6 of 13 Sci Nat (2018) 105: 47
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
on arthropods (Whelan et al. 2008). With this technique, it has
been proven that birds can significantly reduce the abundance
of herbivorous insects in tropical, temperate, and boreal for-
ests (Holmes et al. 1979; Gradwohl and Greenberg 1982;
Atlegrim 1989; Marquis and Whelan 1994; Gunnarsson
1996; Murakami and Nakano 2000; Strong et al. 2000;Van
Bael et al. 2003;Dunham2008; Morrison and Lindell 2012).
Exclosure experiments also show that insectivorous birds can
also have a negative effect on the abundance of herbivorous
insects in grasslands (Joern 1986;Bocketal.1992) and crop-
lands (Hooks et al. 2003; Perfecto et al. 2004; Kellermann et
al. 2008;Koh2008; Johnson et al. 2010;Maasetal.2016).
Negative effects of insectivorous birds on herbivorous in-
sects have been further demonstrated by means of dummy
caterpillar experiments in tropical and non-tropical biomes
(e.g., Maas et al. 2015;Roslinetal.2017).
Which prey taxa are killed by insectivorous birds?
Insectivorous birds eat a large variety of arthropod taxa (e.g.,
Rotenberry 1980b; Poulin et al. 1994; Dyrcz and Flinks 1995;
Gajdošand Krištín 1997;Orłowskietal.2014; Helms et al.
2016; Sam et al. 2017). Seven arthropod orders, Lepidoptera,
Coleoptera, Orthoptera, Diptera, Hemiptera, Hymenoptera, and
Araneae, however, are frequently consumed (Gajdošand Krištín
1997;Wilsonetal.1999; Develey and Peres 2000; Gámez-
Virués et al. 2007; Sam et al. 2017). In temperate forests and
agricultural habitats, caterpillars (Lepidoptera larvae) and bee-
tles (Coleoptera) are particularly common prey of insectivorous
birds (Holmes et al. 1979; Woronecki and Dolbeer 1980;Gajdoš
and Krištín 1997;Jeromin2002;Faytetal.2005; Moorman et
al. 2007; Gilroy et al. 2009; Pagani-Núñez et al. 2017), whereas
grasshoppers (Orthoptera) are usually an essential component in
the diets of grassland birds (Joern 1986;Bocketal.1992; Kobal
et al. 1998). Tropical forest and farmland birds frequently con-
sume beetles, ants, cockroaches (Blattodea), katydids
(Orthoptera), caterpillars, and spiders (Poulin and Lefebvre
1996;Şekercioğlu et al. 2002; Hooks et al. 2003;Koh2008;
Sam et al. 2017). Desert birds frequently feed on beetles, ants,
and termites (Maclean 2013). Termites are an important food
source for birds inhabiting tropical savannas (Korb and
Salewski 2000). In Arctic tundra habitats, birds consume mostly
tipulids (Diptera) and spiders (Araneae)two arthropod groups
numerically dominating the arthropod fauna of the sparse tundra
vegetation (Holmes 1966;Custer and Pitelka 1978).
Relative contribution of different biome categories
to the global annual prey consumption
Birds in forests account for 75% of the annual prey consumption
of the worlds insectivorous birds (300 million tons year
Table 2). Forests cover a large portion of the global terrestrial
surface area (41.6 million km
; Saugier et al. 2001),andinthese
productive and vegetatively complex habitats, birds usually
reach higher diversities (Willson 1974) and numbers ha
pared to non-forested areas (Gaston et al. 2003). A similar trend
of highest predation impact occurring in forested areas has been
reported for spiders (Nyffeler and Birkhofer 2017). Forest birds
feed frequently on potentially harmful caterpillar and beetle pests
(Holmes et al. 1979;Faytetal.2005;Moormanetal.2007). This
is especially true during the breeding season, when passerines
(song birds) catch large numbers of leaf-eating caterpillars to feed
them to their nestlings (Gibb and Betts 1963;Holmesetal.1979;
Gajdošand Krištín 1997; Mols and Visser 2002). At this time of
the year, caterpillars make up 2090% of the nestling diets of
many species of insectivorous birds (Gibb and Betts 1963;
Pravosudov and Pravosudova 1996;Gajdošand Krištín 1997;
Török and Tóth 1999; Pagani-Núñez et al. 2017). Due to high
protein content and easy digestibility, caterpillars comprise an
optimal diet for nestling birds (Tremblay et al. 2005). Data sug-
gest that forest birds exert considerable predation pressure on
lepidopteran pests, such as the eastern spruce budworm
(Choristoneura fumiferana;Holmesetal.1979;Şekercioğlu
2006a). Crawford and Jennings (1989) found that birds
destroyed 84% of larval and pupal eastern spruce budworms at
low densities of this pest. The birds are most effective as natural
enemies at endemic pest densities (Holmes et al. 1979;Holmes
1990). Fayt et al. (2005) pointed out that woodpeckers (Picidae)
suppress the abundance of bark beetles (Curculionidae) in conif-
erous forest landscapes. Furthermore, forest birds at times feed
heavily on spiders, especially during the breeding season (Naef-
Daenzer et al. 2000; Pagani-Núñez et al. 2017). In Scandinavian
boreal forests, spiders are a major diet for overwintering tits
(Parus spp.), treecreepers (Certhia familiaris), and goldcrests
(Regulus regulus) (Askenmo et al. 1977; Gunnarsson 1996).
Spiders are an important food source for birds because of their
high content of taurine, an amino acid that plays a vital role in the
early development of many types of passerine birds (Ramsay
and Houston 2003;Arnoldetal.2007). The propensity for birds
to feed on spiders can reduce some positive economic impact of
avian insectivory because spiders themselves are highly benefi-
cial natural enemies of insects (Nyffeler 2000;Nyffelerand
Birkhofer 2017).Thesameistruewhenbirdsfeedonlarge
numbers of predaceous ants or odonates, as is sometimes the
case in purple martins (Progne subis) and house martins
(Delichon urbicum) (Kelly et al. 2013;Orłowskietal.2014;
Helms et al. 2016).
Birds in grasslands and savannas contributed 15% (i.e.,
60 million tons year
; Table 2) to the global annual prey
biomass. Grasslands and savannas cover a vast area of the
globe (45.4 million km
; Saugier et al. 2001). Included in this
figure are 2.8 million km
Mediterranean shrublands. The
prey biomass ha
of bird communities in the grassland
biome is considerably lower than that in forests (Table 2;Ford
and Bell 1981; Wiens 1989). Notwithstanding that, North
American studies have shown that grassland birds at times
Sci Nat (2018) 105: 47 Page 7 of 13 47
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
exert noticeable predation pressure on grasshopper popula-
tions (Joern 1986;Belovskyetal.1990;Bocketal.1992).
Bird communities associated with agricultural areas contrib-
uted roughly 7% (i.e., 28 million tons year
; Table 2).
Cropland covers an area of 13.5 million km
(Saugier et al.,
2001) Agricultural landscapes are mosaics of crop fields, shel-
terbelts, and tree-lined field roads (Kartanas 1989;Gámez-
Virués et al. 2007). In our estimates ofprey biomass ha
for croplands (Table 2), birds associated with tree-lined field
roads have been taken into account as well (compare Kartanas
1989). Although birds in the agricultural landscape are known
to feed at times heavily on potentially harmful lepidopteran and
coleopteran pests (Woronecki and Dolbeer 1980), examples of
farmland birds substantially suppressing crop pests are few,
which may be explained by the fact that crop fields are usually
inhabited/visited by birds in rather low numbers (Gaston et al.
2003), at least in temperate regions. Reports of birds suppress-
ing agricultural pests refer for the most part to studies in tropical
Table 3 Comparative estimates of the annual prey consumption (kg fresh weight ha
) of different groups of predaceous animals based on
published data
Predator type Biome class Prey biomass
(kg ha
Insectivorous birds Salt marsh 545 Kale 1965
Insectivorous birds Urban areas 84289 Falk 1976; Kartanas 1989
Insectivorous birds Tropical forests 100176 Leigh 1999
Insectivorous birds Temperate forests 35137 Holmes and Sturges 1975;WeinerandGłowaciński 1975;
Keast et al. 1985; Harris 1991
Insectivorous birds Tree-lined field roads 3679 Kartanas 1989
Insectivorous birds Grasslands, crop fields 1031 Ferger et al. 2013; Wiens and Dyer 1975
Piscivorous birds Freshwater lakes and marshes 849 Nilsson and Nilsson 1976; Biujse et al. 1993
Insectivorous primates Tropical forest 1032 Sakai (2002)
Insectivorous bats Tropical forest 4 Kalka and Kalko 2006
Insectivorous bats Carlsbad Caverns national park Low
Combined data Tuttle 1994/BestandGeluso2003
Shrews Taiga forest 25350 Shvarts et al. 1997
Shrews Reed swamp 6 Pelikan 1978
Hedgehogs Reed swamp 1 Pelikan 1978
Lizards Various biome types 39 Shelly 1986; Walter and Breckle 2013
Lizards Woodland on tropical island 85 Bennett and Gorman 1979
Salamanders Temperate forests 7 Burton and Likens 1975
Frogs Tropical forest 1163 Stewart and Woolbright 1996; Walter and Breckle 2013
Frogs Temperate grasslands < 1180 Breymeyer 1978; Pelikan 1993
Ants Tropical forest 21147 Dyer 2002
Ants Temperate forest 177 Horstmann 1974
Ants Temperate grasslands 46536 Kajak et al. 1971
Spiders Tropical coffee plantation 160320 Robinson and Robinson 1974
Spiders Temperate forests 20100 Nyffeler 2000; Nyffeler and Birkhofer 2017
Spiders Temperate grasslands 20230 Nyffeler 2000; Nyffeler and Birkhofer 2017
Spiders Crop fields 10 Nyffeler 2000
Scorpions Arid zone 8 Shorthouse and Marples 1982
Wasps (Vespa) Temperate forest 18Harris1991
Robber flies (Asilidae) Tropical forest 7 Shelly 1986
Ground beetles (Carabidae) Temperate forest, cropland 20 Chauvin 1967;Schaefer1990
Rove beetles (Staphylinidae) Temperate forest 64 Schaefer 1990
Centipedes Temperate forest 100 Schaefer 1990
Original values adjusted when necessary by using correction factors obtained from the literature
Only a few kg arthropods ha
(Nyffeler, unpubl. estimate), taking into account a foraging area with a radius of 50 km for the Mexican free-
tailed bat (Best and Geluso 2003)
47 Page 8 of 13 Sci Nat (2018) 105: 47
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
plantations (e.g., Hooks et al. 2003;Koh2008). A classic ex-
ample of the successful avian control of a pest species comes
from tropical coffee plantations in Costa Rica, Guatemala,
Jamaica, Mexico, Panama, and Puerto Rico, where the coffee
berry borer Hypothenemus hampeiconsidered to be the
worlds most damaging insect pest in coffeeis successfully
controlled by insectivorous avian communities often largely
composed of wood-warblers (Parulidae) (Greenberg et al.
2000; Perfecto et al. 2004; Kellermann et al. 2008; Johnson et
al. 2010; Wenny et al. 2011;Karpetal.2013).
Birds associated with desert and tundra biomes account for
only a small percentage (each < 4%) of the global annualprey
biomass (Table 2). The low prey biomass ha
of birds
in these biome types reflects that such habitats are covered by
a sparse vegetation of low productivity supporting only low
densities of birds (see Gaston et al. 2003). Birds in desert and
tundra habitats prey exclusively on non-pest arthropods dur-
ing their occurrence in these biomes which renders them in-
significant from the perspective of economic ornithology
(Holmes 1966; Custer and Pitelka 1978;Maclean2013).
Concluding remarks
For the first time, the predation impact of the insectivorous
birds has been quantified on a global scale. The global energy
consumption by the insectivorous birds in the form of arthro-
pod prey is substantial (an estimated 2.7 × 10
Annually, the global population of insectivorous birds con-
sumes as much energy as a megacity the size of New York
(2.8 × 10
, in 2011; Kennedy et al. 2015).
To fulfill these huge energy requirements, the insectiv-
orous birds capture billions of potentially harmful herbiv-
orous insects and other arthropods. Only few other preda-
tor groups, such as spiders and entomophagous insects, can
keep up with the insectivorous birds in their capacity to
suppress herbivorous insect populations in a variety of bi-
omes (Table 3;DeBachandRosen1991;Nyffelerand
Birkhofer 2017). Other predator groups like bats, primates,
shrews, hedgehogs, frogs, salamanders, and lizards appar-
ently are less effective natural enemies of herbivorous in-
sects (Table 3). Although some of these latter predator
groups may exert high predation pressure in a particular
biome type (e.g., lizards on tropical islands; see Bennett
and Gorman 1979), these same groups are much less effec-
tive in other biomes so that their global impact cannot
compare to that of spiders, entomophagous insects, or in-
sectivorous birds. The global predation impact of the in-
sectivorous birds (between 400 and 500 million tons year
is approximately of the same order of magnitude as that of
the spiders (between 400 and 800 million tons year
Nyffeler and Birkhofer 2017).
Acknowledgments We are grateful to Steffen Hahn and Lukas Jenni
(both Swiss Ornithological Institute Sempach) and Franz Bairlein
(Institute of Avian Research BVogelwarte Helgoland,^Germany) for pro-
viding us with expert knowledge needed to roughly estimate the food
consumption by migrant birds at stopover sites. We also wish to thank
Thomas Alerstam (Lund University), James Van Remsen (Louisiana
State University), andthree anonymous reviewers for their valuable com-
ments on earlier drafts.
Open Access This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License (http://, which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a link
to the Creative Commons license, and indicate if changes were made.
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Supplementary resource (1)

... Therefore, understanding how the abundance and distribution of insects are affected in the urban landscape may help explain ecosystem functioning and the presence of other groups in cities. Some groups like birds should be directly affected by the presence of insects as they are crucial feeding resources for many bird species (Nyffeler et al., 2018). Furthermore, this information on urban insect communities could be crucial for the use of this group as bioindicator. ...
Full-text available
Human population growth is causing an expansion of urban areas, a phenomenon known to deeply impact on the Earth’s biodiversity. Therefore, it is key to understand how to conceal urban development with biodiversity conservation. In this context, university campuses can play an important role as they usually present a large array of different environments and green areas, crucial aspects for promoting urban biodiversity as well as human-nature interactions. Several studies have analyzed the biodiversity of university campuses, however, there are still important taxonomic (e.g., insects) and geographical biases (e.g., Mediterranean hotspot) in our current understanding of these urban areas. Insects are fundamental in many ecosystems as pollinators, prey, pest controllers or decomposers among others. This further increases the need to study this group in the urban context. In this study, we have investigated diurnal Lepidoptera and ground-dwelling Coleoptera in three university campuses and three non-campus areas of the city of Granada (Spain). We used spatial and temporal replicates for each area in order to explore whether university campuses hold higher levels of insect biodiversity (e.g., species richness or common species) than other nearby urban areas. In addition, we investigated the potential influence of several additional predictors on insect diversity such as type of land cover, vegetation origin, management intensity, and distance to the outskirts. Our results suggest that Lepidoptera species and Coleoptera families are more diverse in university campuses than in other urban areas, showing also a positive association with the proportion of bare soil and herbaceous cover. Furthermore, they also seem to be benefited from low vegetation management intensity whereas Coleoptera are favored by native vegetation providing clear management recommendations in order to promote such animal groups in cities. Our study indicates that university campuses are important urban areas to preserve insect biodiversity but also highlights the heterogeneity of response among insect groups.
... For birds in particular, insect declines could have particularly influential impacts. Insects are the primary food source for 90% of all land birds, which consume an estimated 400-500 million metric tonnes of insects annually (Nyffeler et al., 2018). Within passerines (songbirds)-which comprise the majority of all birds with roughly 6500 species-more than half have a diet composed of at least 70% invertebrates (Wilman et al., 2014). ...
Full-text available
Reports of declines in abundance and biomass of insects and other invertebrates from around the world have raised concerns about food limitation that could have profound impacts for insectivorous species. Food availability can clearly affect species; however, there is considerable variation among studies in whether this effect is evident, and thus a lack of clarity over the generality of the relationship. To understand how decreased food availability due to invertebrate declines will affect bird populations, we conducted a systematic review and used meta‐analytic structural equation modelling, which allowed us to treat our core variables of interest as latent variables estimated by the diverse ways in which researchers measure fecundity and chick body condition. We found a moderate positive effect of food availability on chick body condition and a strong positive effect on reproductive success. We also found a negative relationship between chick body condition and reproductive success. Our results demonstrate that food is generally a limiting factor for breeding songbirds. Our analysis also provides evidence for a consistent trade‐off between chick body condition and reproductive success, demonstrating the complexity of trophic dynamics important for these vital rates.
... In our study, we selected insectivores and frugivores-nectarivores (Wilman et al., 2014). Nectarivores and frugivores are related to nectar and fruit consumption, respectively associated with pollination and seed dispersal services (Sekercioǧlu, 2006), while insectivores perform biological control of arthropod populations (Nyffeler et al., 2018). ...
Latin American cityscapes are growing fast, posing risks to many bird communities and ecosystem services (e.g. seed dispersal and arthropod population control), but few studies have addressed how bird functional diversity respond to urbanization in Neotropical cities. In this study, we tested which biotic (i.e. vegetation characteristics and human and pet disturbances) and abiotic variables (i.e. area size, number of vehicles, and glass panes) influence functional diversity indices of insectivores, frugivores‐nectarivores, migrants, residents, and total bird community at urban green spaces in São Paulo megacity, southeastern Brazil. A rich avian community (235 species) from 25 studied sites was recorded. Generalized linear models (GLM) analyses showed that large‐sized areas of urban green spaces and shrub cover are the main characteristics that drive high bird functional diversity. Small‐sized sites were less favourable for preserving bird functional diversity. We showed that these areas were related to some negative impacts for bird species (e.g. absence of shrub layer, heavy traffic and massive presence of glass panes, and domestic animals), thus causing declines in avian functional diversity. Off‐leash and homeless dogs and cats may cause declines in bird ecological functions (e.g. insect control, seed dispersal and pollination), which are essential to sustain biodiversity. Therefore, as management actions to improve bird diversity and better provisioning of ecosystem functions, we recommend that urban planners and managers should prioritize large‐sized areas with high shrub cover. Additionally, we highlight the need to mitigate the negative impact on birds caused by glass panes, traffic of vehicles, and off‐leash and homeless dogs and cats. Abbreviated abstract summarizing the article: Green large‐sized areas and shrub cover drive higher bird functional diversity.
Avian decline is occurring globally with neonicotinoid insecticides poised as a potentially contributing factor. Birds can be exposed to neonicotinoids through coated seeds, soil, water, and insects, and experimentally exposed birds can show varied adverse effects including mortality and disruption of immune, reproductive, and migration physiology. However, few studies have characterized exposure in wild bird communities temporally. We hypothesized that neonicotinoid exposure would vary temporally and based on avian ecological traits. Birds were banded and blood sampled at eight non-agricultural sites across four Texas counties. Plasma from 55 species across 17 avian families was analyzed for the presence of 7 neonicotinoids using high performance liquid chromatography-tandem mass spectrometry. Imidacloprid was detected in 36 % of samples (n = 294); this included quantifiable concentrations (12 %; 10.8-36,131 pg/mL) and concentrations that were below the limit of quantification (25 %). Additionally, two birds were exposed to imidacloprid, acetamiprid (18,971.3 and 6844 pg/mL) and thiacloprid (7022.2 and 17,367 pg/mL), whereas no bird tested positive for clothianidin, dinotefuran, nitenpyram, or thiamethoxam, likely reflecting higher limits of detection for all compounds compared to imidacloprid. Birds sampled in spring and fall had higher incidences of exposure than those sampled in summer or winter. Subadult birds had higher incidences of exposure than adult birds. Among the species for which we tested more than five samples, American robin (Turdus migratorius) and red-winged blackbird (Agelaius phoeniceus) had significantly higher incidences of exposure. We found no relationships between exposure and foraging guild or avian family, suggesting birds with diverse life histories and taxonomies are at risk. Of seven birds resampled over time, six showed neonicotinoid exposure at least once with three showing exposures at multiple time points, indicating continued exposure. This study provides exposure data to inform ecological risk assessment of neonicotinoids and avian conservation efforts.
Full-text available
Global declines in bird and arthropod abundance highlights the importance of understanding the role of food limitation and arthropod community composition for the performance of insectivorous birds. In this study, we link data on nestling diet, arthropod availability and nesting performance for the Coastal Cactus Wren (Campylorhynchus brunneicapillus sandiegensis), an at-risk insectivorous bird native to coastal southern California and Baja Mexico. We used DNA metabarcoding to characterize nestling diets and monitored 8 bird territories over two years to assess the relationship between arthropod and vegetation community composition and bird reproductive success. We document a discordance between consumed prey and arthropod biomass within nesting territories, in which Diptera and Lepidoptera were the most frequently consumed prey taxa but were relatively rare in the environment. In contrast other Orders (e.g., Hemiptera, Hymenoptera)were abundant in the environment but were absent from nestling diets. Accordingly, variation in bird reproductive success among territories was positively related to the relative abundance of Lepidoptera (but not Diptera), which were most abundant on 2 shrub species (Eriogonum fasciculatum, Sambucus nigra) of the 9 habitat elements characterized (8 dominant plant species and bare ground). Bird reproductive success was in turn negatively related to two invasive arthropods whose abundance was not associated with preferred bird prey, but instead possibly acted through harassment (Linepithema humile; Argentine ants) and parasite transmission or low nutritional quality (Armadillidium vulgare; "pill-bug"). These results demonstrate how multiple aspects of arthropod community structure can influence bird performance through complementary mechanisms, and the importance of managing for arthropods in bird conservation efforts.
Full-text available
Insects and other arthropods are central to terrestrial ecosystems. However, data are lacking regarding their global population abundance. We synthesized thousands of evaluations from around 500 sites worldwide, estimating the absolute biomass and abundance of terrestrial arthropods across different taxa and habitats. We found that there are ≈1 × 1019 (twofold uncertainty range) soil arthropods on Earth, ≈95% of which are soil mites and springtails. The soil contains ≈200 (twofold uncertainty range) million metric tons (Mt) of dry biomass. Termites contribute ≈40% of the soil biomass, much more than ants at ≈10%. Our estimate for the global biomass of above-ground arthropods is more uncertain, highlighting a knowledge gap that future research should aim to close. We estimate the combined dry biomass of all terrestrial arthropods at ≈300 Mt (uncertainty range, 100 to 500), similar to the mass of humanity and its livestock. These estimates enhance the quantitative understanding of arthropods in terrestrial ecosystems and provide an initial holistic benchmark on their decline.
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Genetic methods for species identification are becoming increasingly popular and can accelerate insect monitoring. However, obtaining good DNA quality and quantity from insect traps remains a challenge for field studies. Ethylene glycol, propylene glycol, and Renner solution have been previously suggested as suitable preservatives for the collection of genetic material, but a systematic overview of their performance under compromising field conditions is lacking. Here we experimentally test whether and how different preservatives affect DNA quality under different conditions and evaluate how choice of preservative may affect metabarcoding and more demanding downstream applications (e.g., RADseq). For this, we used the house cricket, Acheta domesticus (L.) (Orthoptera: Gryllidae), and tested propylene glycol, ethylene glycol, and Renner solution for their ability to preserve DNA over 27 days in various dilutions and temperatures. DNA quality was measured as DNA fragmentation and success rates in PCR amplifying a COI fragment of 658, 313, or 157 bp. Undiluted propylene glycol and ethylene glycol always retained high molecular weight DNA at room temperature. No high molecular weight DNA was preserved at 37 °C or in any dilution. Nevertheless, the COI sequence could be amplified from samples at every condition. Renner solution did not preserve high molecular weight DNA and fragmentation increased over time at 37 °C until amplification was impossible. The results suggest that propylene glycol and ethylene glycol are suitable preservatives for collecting both genetic and morphological material, but dilution or high temperatures compromise their ability to preserve high molecular weight DNA. For genomic approaches requiring high DNA quality, additional preservatives may need to be tested.
Generalized crop-specific or regional blanket fertilizer recommendations are among the primary dilemmas for sustainable agriculture resulting in low fertilizer use efficiency, nutritional imbalance in crops, while raising economic and environmental concerns. Innovative fertilizer formulations with balanced nutrient ratios customized to the crop requirements with temporal release properties are needed to make sustainable agriculture practically possible. For an example, the demonstration of the advantages of delayed differentiation, through reverse blending (RB) in small blending units at the end user level may be useful to increase the sustainability of agriculture. This review discusses how to use innovative fertilizer procedures in the fertilizer supply chain to optimize the supply of crop nutrition to boost crop production and safeguard the environment from the drawbacks of blanket fertilizer applications. This review also aims to identify critical elements that influence fertilizer use efficiency and fertilizer customization to improve fertilizer recommendations for future (precision) agriculture, and to assess the role and suitability of RB in the production of customized fertilizers. We reviewed typical case studies and summarized the role of delayed differentiation in the production of field fertilizers through RB. Customized fertilizers could be produced by using smallest sets of canonical basic inputs (CBI). CBI acronym offers the smallest set of chemical composite materials that can be used as a blending input for the production of customized fertilizers. Reverse blending (RB) accelerates the attainment of large flows by decreasing those flows to discover chemically stable reactions for the creation of novel fertilizer formulations. RB drives the high flow massification to low by managing the flow from 100 to 1.57%. RB requires a minimum of 10–15 CBIs (± 0.05%) to meet out nutritional requirements of many crops. Delayed differentiation through RB will involve exploration of known percentage of CBI in terms of N, P, K, Zn, B2O3, and filler to achieve a desirable fertilizer. The tailored fertilizers used for basal application must be granular, with at least 90% of the content ranging between 1 and 4-mm IS sieve, with no more than 5% lying below 1 mm. Moisture content should not be present at more than 1.5%. The paper demonstrates RB as a quadratic model approach where blending is based on geographical area, enabling the crops to achieve target yields through customized fertilizer solution with higher agronomic (kg/ha of N, P, K, Zn, B2O3) applicability. We understand that innovative fertilizer strategies must be developed to significantly reduce unforeseen negative effects on the environment and human health caused by the improper use of fertilizers.
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La production annuelle de graines par la végétation herbacée et leur consommation par les oiseaux, les rongeurs et les fourmis Messor galla ont été étudiées au cours de 3 années successives. La production annuelle de graines a varié de 286 kg/ha à 1 061 kg/ha, les oiseaux en auraient consommé 6 % à 26 %, les rongeurs 1 % à 15 % et les fourmis 0,4 % à 2 % selon les années. Au total, 1/3 à 2/3 des graines produites auraient été consommées si on tient compte de l’impact des insectes endophytophages qui se développent dans les graines de l’espèce dominante Cassia tora (Leguminosae). Globalement, pendant la période d’étude, les quantités de graines n’ont pas semblé un facteur limitant pour les populations granivores et, réciproquement, l’impact des granivores n’a pas paru compromettre le renouvellement de la strate herbacée l’année suivante. Cependant, les différents groupes granivores effectuant des choix parmi les graines disponibles, il est probable qu’il y a compétition pour certaines graines particulièrement recherchées et que leur impact influe sur l’équilibre entre les espèces herbacées. Ces 3 groupes granivores, systématiquement éloignés (oiseaux, rongeurs, fourmis), utilisent certes la même source de nourriture, limitée en quantité et variable dans le temps, mais ils diffèrent quant à leur mode d’utilisation spaciale et temporelle de cette même ressource.
The two volumes of John Wiens' Ecology of Bird Communities have applications and importance to the whole field of ecology. The books contain a detailed synthesis of our current understanding of the patterns of organisation of bird communities and of the factors that may determine them, drawing from studies from all over the world. By emphasizing how proper logic and methods have or have not been followed and how different viewpoints have developed historically and have led to controversy, the scope of these books are extended far beyond the study of birds. Processes and Variations discusses the way in which bird community patterns have been interpreted. This second volume examines how the complexity and variability of natural environments may influence efforts to discern and understand the nature of these communities. Graduate students and professionals in avian biology and ecology will find these volumes a valuable stimulus and guide to future field studies and theory development.