CAUSES OF MORTALITY OF THE SHORT

CAUSES OF MORTALITY OF THE SHORTZARED OWL IN SPAlN
131
FIG. l.-A: Comunidades Aut6nomas where the study has been carried out. 1: Gaüeia; 2: CastillaLe6n; 3: Pals Vasco; 4: Cataluna; S: Asturias; 6: Madrid; 7: Castilla-La Mancha; 8: Extremadura; 9:
Andaluda; 10: Comunidad Valenciana; 11: Murcia. B: Preferential wintering areas accordmg lo the
bibliography and the data dislribution recorded lor this study. 1: Northem halfof the Central plateau.
Cantabrian eoastal sirip and Galicia; 2: Eastem and southern coast.
[A: Comunidades Autdnomas donde el estudio se ha llevado a cabo. 1: Golicia; 2: Castilla-Le&: 3: Pafs
Vasco; 4: Catalufla: 5: Asrurias: 6: Madrid; 7: Casrilla-La Mancha; 8: Extremadura: 9: Andalucla; 10:
Comunidad Valenciana: 11: Murcia. B: Areas prefirenciales de invernada de acuerdo con la bibliograíla y la
disrribircidn de daros aporrados por este estudio. 1: Subniesera Norte,/ronja costera canfdbrica y Galiua; 2:
Levante y cosra andaluza.]
The detennination of the cause of death
has been done based on the circumstances in
which the bodies were found and the postmortem examination by the clinical persone1
of the rescue centres, method already used by
other authors (Marti, 1984; Kerlinger & Lein,
1988; Fajardo, 1990).
areas are signilicant (1:=4.49, P<0.05) being
larger in Z1.
This cause acquires a similar value in Bubo
bubo with 62.6% (Hemández, 1990) bu1 a
secondary importance in Tyco alba with
15.5 % (Fajardo, 1990).
Other recorded causes in order of importance are: a) birds found exhausted or emaciated, b) road traflíc accidents (RTAs), c)
trapped birds, d) unknown causes, and e) collisions with electric lines.
The distnbution is not unifonn between
A total of 205 death cases of Asioflammeus
have been linally considered and can be clas- research areas. There are highly significant
silied according to their cause, area and d a - differences between 2, and Z, in cases of
tive value as shown in table 1. OI these, RTAs and trapped birds, which are conside72.2% (n=148) of the total cases belong to rably larger in research area 2(~:=10.27,
the study area 1, the remaining 27.8% P<0.01 for RTAs and ~:=8.97, Pt0.01 for
( n = 5 7 ) belong to area 2. Figure 2 represents trapped birds).
The losses produced by RTAs are a small
the monthly distribution of the total mortality and its distribution in both research proportion of the total (8.3 % for the lberian
areas. The highest percentage detected co- peninsula, 4.1 % for Zl). However, in 2 2 the
rresponds to shooting (70.2 %), an overw- proponion is considerable (18.3%). In the
helming value if compared to the rest of the case of other Ibenan Stngifomes (Tyta alba
recorded cases. The diNerences between both and Athene noctua). this cause ofmortality is
TABLE
1
Short-ea4 Owl mortality in Spain. Absolute and relative valuu of cach mortality faaor are includcd for
both studied zones and totals.
[Mortalidad de LechuzaCmpestre en EspriAe Se representan los valores absolutos y relatlws de cada emua
registroda para ambas r o ~ des estudio y el total.]
Total
N
Shot ................................................ 144
Emaciated or exhausted ....................... 26
Rta ..................................................... 17
Trapped ..............................................
9
Unknown ............................................
7
2
Electrocutcd ........................................
205
Zone 2
Zone 1
%
N
%
N
%
70.2
12.6
8.29
4.3
3.4
0.97
110
25
34
1
11
58.6
2
5
74.8
16.3
4.08
1.3
3.3
O
O
6
148
7
2
2
1.7
18.9
12
3.4
3.4
S7
of primary importance and lar above the rest concentration o1 the facton that propiciate
(36.5 % lor T. alba).
RTAs for this species (for a description of
Emaeiation is an important c a u s in area these factors see Fajardo et al., 1992). The
1, and the difference is highly significant higher toll of trapped birds in area 2 is caubf=7.41, P=O.Ol).
sed by a charactenstic and traditionally poThe otber causes are not o1 great impor- pular type of trap called xparanyr, which actance in our sample as their values are always counts for the death of many migratory birds
under 5 % for both areas. If we add the va- each year (pers. obs. G.E.R.).
lues of the mortalities caused directly or indiThe importance of direct or indirect hurectly by man, we reach a stunning 83.9 % man factors, as causes o1 death, in both zones
(n= 172) of the total (80.2 %, n = 118, for area separately and as a whole, is so worrying that
1and 93.1 %, n=54, for area 2). ?he diíferen- it could be considered as a cause o1 populaces between Z, and Z, are significant tion decline, as it occurs with other owls
lx: =4.15, P-zO.05).
(Colvin, 1985; Hernández, 1988; Fajardo,
1990, Fajardo et al.. 1992).
The considerable difference between r e
search areas in the relative values of mortality caused by emaciation is diliicult to interThe temporal distribution 01the mortality pret biologically.
For other irruptive wintering owls like the
o1Asioflammeus in Spain shows great similaSnowy Owl (Nyctea scandioca), the imporrity to its phenology.
On the other hand, the spatial &%tribu- tance oi the mortality caused by starvation is
tion of data seems to confirm the possible proportionally low (14.1 %). However, this
existence o1 two preferential wintering and/or amount tends to grow m perifenc zones of
migratory areas for this species in the Iberian their wintering areas (Kerlinger & Lein, 1988).
peninsula, as other authors have already Considering the great similitude in the irregular and it-ruptive migratory behaviour of both
pointed out (Asensio et al., 1992).
As far as the different mortality causes are species (Sparks & Soper, 1991), the wncluconcerned, shooting is by far the most impor- sions reached for the Snowy Owl might be
tant cause of death in ihe whole o1 the wun- extrapolated and applied to this study of Asio
try and therefore the main threat for the po- flommeus in S p a h In that m e , the importance of emaciation would depend on the year.
pulation ol this wintering owl.
It can Iinally be concluded that the manaThe increased mortality by collisions with
vehicles in area 2 can be due to a higher gement of the species in Spain should first
CAUSES OF MORTALITYOF THE SHORT-EAREDOWL M SPAIN
133
FE. 2.-Monthly distribution o1 Short-eared Owl mortality in both zones and the total.
[Distribucidn mensual de la mortalidad de la Lechuza Campestre paro las dos zonas y el total a lo largo del
arlo.]
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human factors might cons:itute a cause o[
regression of the breeding population.
-.
134
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[Recibido: 13.12.931
[Aceptado: 14.6.941