https://www.science.org/doi/10.1126/science.abo5970 eLetter: MAY. 17, 2022
Endogamy risk and osprey translocations: a reply
Miguel Ferrer1*, Alan Poole2, Ian Newton3, Roy Dennis4, Des Thompson5, Roberto Muriel1,
Juan Jimenez6, Virginia Morandini7, 8,9
1 Applied Ecology Group, Estación Biológica de Doñana (CSIC), Sevilla, Spain.
2 Cornell Lab of Ornithology, Cornell University, Ithaca, Nueva York, USA
3 Centre for Ecology and Hydrology, Huntingdon, Cambs. PE28 2LS, UK.
4 Wildlife Foundation, Scotland, UK
5 NatureScot, SIlvan House, 231 Corstorphine Road, Edinburgh EH12 7AT, UK
6 Wildlife Service. Generalitat Valenciana. Valencia. Spain
7 Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR., USA
8 Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain.
9 Fundación Migres, CIMA, N-340 km 85, E-11380 Tarifa, Spain.
* Corresponding author: Miguel Ferrer, email@example.com
Recently, Monti et al. (1) published a letter encouraging the cessation of an Osprey
reintroduction program started four years ago on the Valencia coast of eastern Spain. They gave
four reasons: (1) source population (northern Europe) differs genetically from the original one;
(2) source population differs in migratory behavior; (3) project does not focus on conservation
but on short-term social and political benefits; (4) the project is not following the
recommendations of international conservation agencies. We advise that these concerns are
erroneous and disingenuous.
Taking these points in turn, all previous studies looking for genetic differences among
geographically separated Osprey populations in Europe and Africa, using DNA microsatellite
markers, give the same results: so far, no consistent differences among European-African
populations of this species have been detected (2, 3). This finding emerged in papers of Monti et
al. (4, 5), even if they do not mention it in the letter. They did not find significant differences in
DNA microsatellite markers among European populations, but found some slight differences
between Mediterranean island populations and north Europe populations with a higher level of
allele-sharing among individuals from the Mediterranean region. This is not surprising,
considering the isolation and endogamy that small island populations have experienced since
the extinction of continental populations in the beginning of the XX century. This level of allele
sharing is an additional argument to encourage reintroductions on the continental shores of the
Mediterranean Sea. We know of no evidence of genetic differences in DNA microsatellite
markers among European population (including Mediterranean islands) to support their spurious
argument about the Mediterranean population being genetically distinct. There are also no
significant differences in the appearance of the birds.
Second, Monti et al. advise against translocations of young Ospreys from northern Europe due
to different dispersal behavior shown by the donor and recipient Mediterranean islands
populations. The former performs long migrations to wintering areas in Africa, while the latter
moves only short distances and may even stay year- round close to the breeding territory (in the
case of the adults) or close to the natal territory (in the first-year juveniles). In fact, this is a
common global pattern in long-lived birds on many islands around the world. It is known that
large birds with deferred sexual maturity tend to be sedentary on islands, and that they become
so even when they are migratory on the nearest mainland (6). This is supported by analyses of
the movement ecology of continental and insular populations of 314 species of raptors, 113
species of Ciconiiformes and 136 species of passerines all over the world, along with individual-
based population simulations (6). Furthermore, among the eight young Ospreys released so far
in the Valencia project, (four coming from Balearic Islands, and four from the reintroduced
Andalusia population), no differences between island and continental donor populations in
migratory behavior have been observed. Birds that were from Balearic Islands became
migratory as soon as they were released in the continental shoreline of Valencia, confirming the
well-known environmental influence in migratory behavior (6). Authors of the letter are aware
of this phenomenon because Ospreys originating from the island of Corsica that they released
on the Italian mainland performed long distance migrations, unlike Corsican birds but in line
with other continental birds (7).
Third, Monti et al. state that, the Valencia Osprey project is not driven by conservation interests,
but by short-term social and political benefits. This is false, and offensive to conservation
scientists involved in the project. The Valencia project has adhered to the scientific guidance
and criteria desirable in any reintroduction (8), including viability analyses, population
simulations, genetic considerations, mortality factors, etc. In doing so, we have adhered to the
IUCN guidelines highlighting the importance of social considerations in any reintroduction
Furthermore, Monti et al. claim that the Valencia project is not following the recommendations
of international conservation agencies. Again, this is false. The advice given in the ‘Recovery
Action Plan for Ospreys in Europe and the Mediterranean Region in particular’ of the Council
of Europe (9), states “after the incipient evidence of endogamy in islands, reintroductions in
Spain, Italy, France, Corsica, Morocco, Portugal and Tunisia using northern countries in Europe
as donor populations are strongly recommended”. The new reintroduced population in southern
Spain (currently around 30 occupied territories) now contains breeding females from Morocco
and from one of the Balearic Islands. The techniques are now well tested and have been shown
to be successful.
Turning away from the spurious comments by Monti et al., we congratulate the scientific
community and the Spanish environmental authorities for initiating these necessary projects,
with the highest standards of international assessments and scientific recommendations.
Globally, we face a nature crisis, and we need to see wholescale support to recover as soon as
possible the former continental Osprey populations in the Mediterranean basin, including the
impoverishment of genetic diversity experienced by island populations, resulting largely from
past human persecution of Ospreys in the region. Restoring the former coastal population in the
Mediterranean basin, using northern populations as a source, will increase the metapopulation
connections, increasing the resilience of the European population and decreasing the genetic and
demography risk for island populations.
The global biodiversity crisis requires nature conservationists to concentrate on large scale
recovery of ecosystems and populations, being a good example the reintroduction of Peregrine
Falcons to North America; one of the great conservation success stories of our generation. For
the Osprey in Europe, the goal must be to have a viable contiguous population occupying all of
its ancestral lands, from the North African coast to the Arctic Circle. Obviously, genetic
considerations, as many other points, must be legitimated for any reintroduction proposals, as
the Valencia Osprey project did. However, the preservation of inbreeding should not be a goal
for species conservation.
1. Monti et al., Science, 376, 468 (2022).
2. J. Helbig, D. Schmidt, I. Seibold, Biol. Cons. Fauna. 102, 224 (1998)
3. Wink, H. Sauer-Gürth, H. Witt. Phylogenetic differentiation of the Osprey (Pandion
haliaetus) inferred from nucleotide sequences of the mitochondrial cytochrome b gene.
In Chancelor, R.D. & Meyburg, B.U. (eds) Raptors Worldwide. Berlin: WWGBP.
4. Monti et al. BMC Evol. Biol. 15, 255 (2015).
5. Monti et al. Conserv. Genet. 19, 839 (2018).
6. Ferrer et al. PLoS ONE 6, e22056 (2011).
7. Monti et al. Ibis.doi: 10.1111/ibi.12567 (2018).
8. International Union for Conservation of Nature Species Survival Commission,
IUCN/SSC “Guidelines for reintroductions and other conservation translocations”
9. Dennis, “Recovery Action Plan for ospreys in Europe and the Mediterranean Region in
particular”. Convention on the Conservation of European Wildlife and Natural Habitats.
Standing Committee, 35th Meeting Strasbourg, 1-4 December 2015. Council of Europe