Current distribution and population size of the Barred Warbler Sylvia nisoria in South Tyrol (Italy)

Abstract

The Barred Warbler Sylvia nisoria is a critically endangered breeding species in Italy, given the severe decline suffered in the last decades and the reduced population size. South Tyrol, an inner Alpine region, is the northernmost Italian breeding area of this warbler, but we lacked recent information about the distribution and population size. In this study, based on surveys carried out in the year 2019 and other recent observations, we assessed a very restricted current distribution of this warbler, and we estimated a population size of 10-30 pairs. We also observed a singing male at unusually high elevation. A comparison of our results to historical data suggests a strong reduction in distribution compared to the 1980s/1990s. The changes in agricultural practices of the last decades might have contributed to determine such decline. Appropriate conservation measures are urgently needed to try to avoid the local extinction of the species.

Full text

© 2020 CISO – Centro Italiano Studi Ornitologici 29
Short communications
1 Museum of Nature South Tyrol - Via Bottai 1, 39100 Bolzano, Italy
2 Eurac Research, Institute for Alpine Environment, Drususallee 1, 39100 Bozen/Bolzano, Italy
3 Ufficio Valutazione dell’impatto ambientale, Provincia Autonoma di Bolzano, Via Amba Alagi 35, 39100 Bolzano, Italy.
4 Via Rovigo 30/5, 39100 Bolzano, Italy
5 Arbeitsgemeinschaft für Vogelkunde und Vogelschutz Südtirol, Maria-Hilf-Straße 5/3, 39011 Lana (BZ), Italy
6 Ufficio Parchi Naturali, Provincia Autonoma di Bolzano, Via Renon 4, 39100 Bolzano, Italy
* Corresponding author: francesco.ceresa01@gmail.com
Francesco ceresa1,*, Matteo anderle2, leo Hilpold3, roberto Maistri4,
oskar niederFriniger5, renato sascor6, petra kranebitter1
Current distribution and population size of the Barred Warbler
Sylvia nisoria in South Tyrol (Italy)
https://doi.org/10.30456/AVO.2020101 Avocetta 44: 29-31 (2020)
The Barred Warbler Sylvia nisoria is a migratory passer-
ine bird breeding from Central Europe through Mongolia
and Western China. In Italy, this warbler breeds at its west-
ern range limit, mostly at the Alps foothills and valleys
in the North of the country (Brichetti & Grattini 2010).
The Italian breeding population suffered a severe decline
in the last decades, and the population size has been re-
cently estimated in less than 100 pairs (Brichetti & Grattini
2010). For these reasons, the species is currently classied
as ‘Critically Endangered’ at the national level (Peronace
et al. 2012). In such a critical situation, detailed informa-
tion about the distribution and abundance of this species
is urgently needed for conservation. In this study, we pre-
sent recent and detailed information about the Barred War-
bler in South Tyrol, the northernmost Italian breeding ar-
ea. This is an inner Alpine region, where the species was
known to breed mainly on the dry and bushy slopes of the
Venosta valley, and more sparsely in other areas (Nieder-
frininger et al. 1996). However, recent information is very
scarce and exclusively based on occasional observations
(Brichetti & Grattini 2010, AVK 2018), therefore the cur-
rent local distribution and population size of the species
are virtually unknown. In the neighbouring Trento prov-
ince, recent surveys allowed detecting 13-15 breeding
pairs in the Fiemme valley and 5-9 in the Non valley, with
more scattered observations in other areas, and the species
is probably declining (Assandri G. & Pedrini P./MUSE,
unpub. data).
During the year 2019, we surveyed Barred Warblers
(as well as other farmland bird species) across 20 study ar-
eas in South Tyrol, overall covering approximately 1,600
ha (mean study area extension = 80.6 ha, range = 23.5 –
124.8 ha). These areas were located between 700 and 1950
m, and all included bushy areas and/or hedgerows, within
a matrix of open habitats like meadows, pastures or elds.
Each study area was surveyed twice, the rst between 25
May and 19 June and the second between 20 June and 15
July, with at least 10 days elapsing between visits at the
same area. We expected low Barred Warbler breeding den-
sity, hence we used a standardized playback procedure to
Abstract – The Barred Warbler Sylvia nisoria is a critically endangered breeding species in Italy, given the severe decline suffered in the
last decades and the reduced population size. South Tyrol, an inner Alpine region, is the northernmost Italian breeding area of this war-
bler, but we lacked recent information about the distribution and population size. In this study, based on surveys carried out in the year
2019 and other recent observations, we assessed a very restricted current distribution of this warbler, and we estimated a population size
of 10-30 pairs. We also observed a singing male at unusually high elevation. A comparison of our results to historical data suggests a
strong reduction in distribution compared to the 1980s/1990s. The changes in agricultural practices of the last decades might have contrib-
uted to determine such decline. Appropriate conservation measures are urgently needed to try to avoid the local extinction of the species.
Key-words: Alps; farmland birds; montane grasslands; threatened Italian birds.

Short communications
30
improve detectability (1 minute of stimulation followed
by 1 minute of listening). This procedure was carried out
across the entire study area, in correspondence of potential-
ly suitable nesting habitat (i.e., occurrence of bushes/low
trees, Brichetti & Fracasso 2010), and at a minimum dis-
tance of 200 m between individual playback points. Given
the territory size of the species (0.11 – 2.59 ha, Aymí et al.
2020), such a distance should effectively prevent double
counts, and at the same time, it should provide an adequate
density of playback points. To complement our survey da-
ta, we also considered the very few occasional observa-
tions of Barred Warblers available from the database of
the Museum of Nature South Tyrol (hereafter MNST) for
the last ve years (2015-2019), as well as one observation
from the Biodiversity Monitoring South Tyrol (Eurac Re-
search) in the year 2019. These additional records are re-
ferred to singing males observed in June.
We observed Barred Warblers at 6 out of 20 study ar-
eas, and we mainly detected singing males (overall, 8 dur-
ing the rst survey period and 6 during the second one).
In the study areas where we detected the species, densities
were very low and ranged between 0.1 and 0.4 males/10
ha. In most cases, birds were observed during both survey
sessions and approximately at the same locations, indicat-
ing that they were more likely breeding individuals rather
than late migrants or prospecting males without a territory/
mate. One singing male was observed on 14 June at 1840
m, an unusually high elevation for this species (see Bri-
chetti & Fracasso 2010). This observation occurred near
the main Alpine watershed, on southeast-facing pastures
with scattered bushes and trees (mainly young conifers) in
the municipality of Moso in Passiria. We did not nd any
records at similar or higher elevations for Italy and for the
Alps in the literature, while an observation at 1900 m is
reported in the MNST database (20 June 2000, 3 singing
males; O. Niederfriniger).
Based on our surveys and other aforementioned data,
the Barred Warbler still occurs during the breeding season
in restricted areas of South Tyrol (Fig. 1), i.e., several areas
of the Venosta valley and few scattered sites in the Isarco,
Pusteria and Passiria valleys, with a minimum population
size of 10 breeding pairs. We could not check some other
potentially suitable sites, and especially the high Venosta
valley could host more breeding pairs than we detected.
Even so, in our opinion a population size larger than 30
pairs is highly unlikely because we sampled a large part
of the few areas in South Tyrol that still maintain adequate
habitat characteristics for the species, detecting very low
densities.
Comparing our results to the past Barred Warbler dis-
tribution and abundance in South Tyrol is problematic, as
the data available for the past decades almost only consist
in occasional observations, or in episodic surveys of re-
stricted areas (Brichetti & Grattini 2010, AVK 2018). Even
so, a temporally explicit map for the period 1980-2010
(from MNST database) and the current estimated distribu-
tion (Fig. 1) clearly suggest a strong range restriction. In
addition, previously published density data and the number
of individuals recorded per site during some occasional ob-
servations strongly suggest higher abundance than indicat-
ed by our surveys, at least until the 1990s (e.g., 12-15 sing-
ing males/30 ha, Berg-Schlosser 1981; 5 pairs along 0.5
km of hedgerows, Niederfriniger et al. 1996). The assumed
decrease is consistent with the strong decline observed at
a national level. The causes of this decline in Italy are not
completely clear, but could include agriculture intensica-
Figure 1. Past (a) and current (b) distribution of the Barred Warbler in South Tyrol, Italy. The past distribution (1980-2010) has been as-
sessed by conservatively selecting occasional observations, trying to avoid including migratory individuals (we mostly used records from
June and July). The current distribution has been assessed by targeted surveys (year 2019) and few recent occasional observations. Black
squares: 2x2 km occurrence cells; circles: survey areas were the species was not detected.
50 km0
1980 - 1986
1987 - 1993
1994 - 2001
2002 - 2010
A B

31
Barred Warbler in South Tyrol, Italy
tion (i.e., removal of hedgerows and bushes, pesticide use)
and land abandonment, as well as environmental and cli-
matic changes in the wintering areas (Brichetti & Grattini
2010, Nardelli et al. 2015). Comparably in South Tyrol, the
Barred Warbler population decline is probably related to
a combination of agricultural intensication and land-use
changes, as the traditional heterogeneous and low-inten-
sity farmed landscape has been widely replaced by inten-
sively managed apple orchards, vineyards and hay mead-
ows, while less productive and accessible grasslands were
partly abandoned (Tasser et al. 2007). As an example, the
dry grasslands of Venosta valley, which represented a wide
and continuous suitable area for the Barred Warbler, were
largely abandoned (more than 70%) and replaced by forests
starting from the 1960s (Tasser et al. 2007). Despite its re-
duction, the Barred Warbler population of South Tyrol has
national relevance, given the low number of pairs breeding
in Italy. Therefore, we encourage the local authorities, in
collaboration with the relevant stakeholders, to implement
the appropriate conservation measures to avoid the local
extinction of this species, such as promoting low-intensi-
ty grazing and farming practices and maintaining and cor-
rectly managing the remaining hedgerows and bushy ar-
eas (see, e.g., Brambilla & Pedrini 2014). These measures
would benet also several other bird species with similar
ecological requirements (e.g., Ceresa et al. 2012, Brambil-
la & Pedrini 2014, Assandri et al. 2019 a,b). We strongly
warn against further land-use changes from grasslands to
orchards and berries cultivations, as well as against further
removals of marginal elements such as bushes, hedgerows
and patches of untilled vegetation.
Acknowledgements – The present study has been nanced by the
Research fund of the Museums of South Tyrol, within the project
‘The distribution and conservation status of birds in South Tyrol’,
CUP H53C17000260005. This study was also supported by the
‘Ufcio Valutazione dell’impatto ambientale – Agenzia provinciale
per l’ambiente (Provincia Autonoma di Bolzano)’. We are grate-
ful to Michele Caldonazzi, Sandro Zanghellini, Alessandro Marsilli
and Alberto Bertocchi, who carried out part of the eldwork.
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Received: 02.01.2020
First response: 23.01.2020
Final acceptance: 01.03.2020
Associate editor: Giacomo Assandri
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