Climate change and human pressure mean migration may be 'no longer worth
it'

Date:
October 18, 2021
Source:
University of Bath
Summary:
Researchers have found that the benefits of migration have been
eroded by the effects of climate change and human pressure.



FULL STORY ========================================================================== Animals that migrate north to breed are being put at risk by ongoing
climate change and increasing human pressure, losing earlier advantages
for migration, declining in numbers and faring much worse than their
resident counterparts, according to scientists writing in Trends in
Ecology & Evolution.


==========================================================================
Many animals, including mammals, birds and insects migrate long distances
north to breed, taking advantage of the seasonally plentiful food,
fewer parasites and diseases, and the relative safety from predators.

However, the international research team, including scientists from the University of Bath, found changes in climate and increasing human pressure
have eroded these benefits and in many cases led to lower reproductive
success and higher mortality in migrating species.

The researchers warn that reduced advantages for long-distance migration
have potentially serious consequences for the structure and function
of ecosystems.

They highlighted 25 recent studies, describing how migration is becoming
less profitable for various terrestrial animals, including caribou,
shorebirds and Monarch butterflies, which migrate over 1000km during the
summer to north temperate and arctic regions to breed, returning south
in the winter.

Travelling such long distances is very costly in terms of energy but the benefits of food supply, fewer diseases and predators meant the benefits outweighed the cost, however the researchers say this is no longer the
case for many populations.



========================================================================== Whilst some animals might shift their breeding ranges slightly further
north to compensate for the change in environmental conditions, migratory animals are hardwired to continue the dangerous trip each year to breed, despite the lack of benefit.

Dr Vojt?ch Kubelka, the leading author and former Visiting Researcher
at the University of Bath's Milner Centre for Evolution, said: "These
findings are alarming. We have lived with the notion that northern
breeding grounds represent safe harbours for migratory animals.

"On the contrary, numerous Arctic and North temperate sites may now
represent ecological traps or even worse degraded environments for
diverse migratory animals, including shorebirds, caribou or butterflies."
Food supplies and availability in the North may be climatically mismatched
with reproduction of migratory animals, incurring higher offspring
mortality, as described for many migratory birds.

Also new parasites and pathogens are emerging in the Arctic, creating
new pressures, and top predators are increasingly preying on nests and
eating eggs and chicks before they get a chance to fledge.



==========================================================================
Dr Kubelka said: "Lemmings and voles used to be the main food source for predators such as foxes in the Arctic, however the milder winters can
cause rain to fall on snow and then re-freeze, preventing the lemmings
from reaching their food." "With fewer lemmings and voles to feed on,
foxes eat the eggs and chicks of migratory birds instead.

"We've seen that rates of nest predation of Arctic migratory shorebirds
has tripled over the last 70 years, in large part due to climate change."
The authors suggest that Arctic and northern temperate breeding grounds
need substantial conservation attention, in addition to well-recognised problems at stopover sites and wintering areas of migratory species.

Next to the concrete conservation measures, the authors propose a simple framework on how to map the stressors for migratory animals across the
space and time, helping to distinguish among suitable, naturally improved
or protected habitats on one hand and the ecological traps or degraded environments with reduced or eroded benefits for migratory behaviour on
the other hand.

Dr Kubelka said: "The recognition of emerging threats and the proposed framework of migration profitability classification will help to identify
the most endangered populations and regions, enabling the implementation
of suitable conservation measures." Professor Tama's Sze'kely, Royal
Society Wolfson Research Merit Award holder at the University of Bath's
Milner Centre for Evolution, said: "Animal migration from equatorial
regions to the North temperate and the Arctic is one of the largest
movements of biomass in the world. But with reduced profitability
of migration behaviour and smaller number of offspring joining the
population, the negative trend will continue and fewer and fewer
individuals will be returning back to the North.

"The Earth is a complex ecosystem -- changes in migration profitability
affect populations of migrating animals which precipitate in alterations
of species composition, trophic food webs as well as the whole ecosystem functioning.

"These patterns are particularly threatening for migratory animals as
large numbers of those species are already negatively affected outside
the breeding period, at their stopover sites and wintering grounds -- and
many have formerly relied on the northern latitudes to provide relative
safe breeding grounds." Professor Rob Freckleton, from the School of
Ecology and Evolutionary Biology at the University of Sheffield, said:
"Our review highlights that there are possible threats to migratory
species. There is a need for more research, and our article highlights solutions are really difficult because of the large areas involved." ========================================================================== Story Source: Materials provided by University_of_Bath. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Vojtěch Kubelka, Brett K. Sandercock, Tama's Sze'kely,
Robert P.

Freckleton. Animal migration to northern latitudes: environmental
changes and increasing threats. Trends in Ecology & Evolution,
2021; DOI: 10.1016/j.tree.2021.08.010 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211018130400.htm

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