by Lucy Capstick, BA (Oxon), MSc.
The numbers of many of the UK’s most well-known
songbirds
continue to fall, despite widespread
conservation efforts.
Farmland birds, for example, declined by 13%
between
2003 and 2011.The ongoing loss of these
birds, whose songs are characteristic of
the British
countryside, is thought to have a number interacting
causes, from
habitat changes to increases in predation.
Some members of the corvidae (the family of birds
which includes crows and magpies) have been shown
to be predators at the nests of songbirds. Many of these
birds have flourished in recent years; the number of
magpies in the UK trebled between 1970 and 1990.
However it is unclear whether or not predation by this
larger corvid population has contributed to the decline
in songbird population.
Previous studies looking at national population trends
have been unable to establish a clear link between
songbird decline and corvid population growth. In
studies where the population of corvids, and other
predators, have been controlled, the effect on songbird
populations has varied. It has been suggested that one
reason for this unclear picture is that some individual
corvids take many eggs and nestlings from songbird
nests whereas other individuals take very few or none.
If this is the case then songbirds will only benefit from
corvid management if those particular corvids which
predate a lot of nests can be accurately identified, and
then selectively controlled.
A research project (funded jointly by the University
of Exeter and SongBird Survival, in collaboration with
the Game and Wildlife Conservation Trust) aims to
explore this hypothesis. The project will investigate whether,
and how, individual crows differ in their predation behaviour.
A key focus will be on the differences between two main
groups in the corvid population; territorial and non-territorial
individuals. Within crow and magpie populations some birds
will form breeding pairs and will establish and defend a
territory during the breeding season (territorial birds)
where as other birds may form pairs but will not be able
to hold a territory (non-territorial birds). We may expect
that territorial birds have the highest impact on songbird
populations because they frequent and get to know particular
areas, watching the nest building or chick provisioning activity
of the songbirds, and so can easily find and predate nests.
Alternatively, it may be that itinerant birds have the highest
impact on songbirds, because they cover larger areas and so
encounter more nests, even if they cannot exploit them so
efficiently. However, it is likely that there will be factors aside
from territorial status that influence predatory behaviour in
individuals and the study will aim to explore this as well.
The project will involve tagging and subsequently tracking
individual crows, both territorial and non-territorial, to
see how they use their habitat and where they find
their food. At the same time the local songbird population
will also be observed, their nests will be located and
monitored using cameras to see how many eggs and
nestlings are taken and which species are taking them.
Additionally, it is intended that other more advanced
technologies, such as stable isotope analysis of feathers,
will be used to aid the investigation into the corvids’ diet
and foraging behaviour.
This investigation should provide insight into whether
territorial and non-territorial birds have differing impacts on
songbird nesting success, and whether each group are
more or less susceptible to legal con
trol methods. It is hoped that the results of this work will
help inform more effective, better targeted, management
of corvid populations, thus benefitting Britain’s threatened
songbirds. This kind of research is designed to help us better
understand why songbirds populations continue to decrease,
and is vital if we are to halt, or even reverse, the loss of these
birds from our countryside.
which includes crows and magpies) have been shown
to be predators at the nests of songbirds. Many of these
birds have flourished in recent years; the number of
magpies in the UK trebled between 1970 and 1990.
However it is unclear whether or not predation by this
larger corvid population has contributed to the decline
in songbird population.
Previous studies looking at national population trends
have been unable to establish a clear link between
songbird decline and corvid population growth. In
studies where the population of corvids, and other
predators, have been controlled, the effect on songbird
populations has varied. It has been suggested that one
reason for this unclear picture is that some individual
corvids take many eggs and nestlings from songbird
nests whereas other individuals take very few or none.
If this is the case then songbirds will only benefit from
corvid management if those particular corvids which
predate a lot of nests can be accurately identified, and
then selectively controlled.
A research project (funded jointly by the University
of Exeter and SongBird Survival, in collaboration with
the Game and Wildlife Conservation Trust) aims to
explore this hypothesis. The project will investigate whether,
and how, individual crows differ in their predation behaviour.
A key focus will be on the differences between two main
groups in the corvid population; territorial and non-territorial
individuals. Within crow and magpie populations some birds
will form breeding pairs and will establish and defend a
territory during the breeding season (territorial birds)
where as other birds may form pairs but will not be able
to hold a territory (non-territorial birds). We may expect
that territorial birds have the highest impact on songbird
populations because they frequent and get to know particular
areas, watching the nest building or chick provisioning activity
of the songbirds, and so can easily find and predate nests.
Alternatively, it may be that itinerant birds have the highest
impact on songbirds, because they cover larger areas and so
encounter more nests, even if they cannot exploit them so
efficiently. However, it is likely that there will be factors aside
from territorial status that influence predatory behaviour in
individuals and the study will aim to explore this as well.
The project will involve tagging and subsequently tracking
individual crows, both territorial and non-territorial, to
see how they use their habitat and where they find
their food. At the same time the local songbird population
will also be observed, their nests will be located and
monitored using cameras to see how many eggs and
nestlings are taken and which species are taking them.
Additionally, it is intended that other more advanced
technologies, such as stable isotope analysis of feathers,
will be used to aid the investigation into the corvids’ diet
and foraging behaviour.
This investigation should provide insight into whether
territorial and non-territorial birds have differing impacts on
songbird nesting success, and whether each group are
more or less susceptible to legal con
trol methods. It is hoped that the results of this work will
help inform more effective, better targeted, management
of corvid populations, thus benefitting Britain’s threatened
songbirds. This kind of research is designed to help us better
understand why songbirds populations continue to decrease,
and is vital if we are to halt, or even reverse, the loss of these
birds from our countryside.
