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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 1. March 2012 
The Wilson Journal of Ornithology 124(1): 162-165, 2012 
Aromatic Plants in Eurasian Blue Tit Nests: 
The *Nest Protection Hypothesis’ Revisited 
Barbara A. Pires, 1 Anabela F. Belo, 24 and Joao E. Rabaga 3,4,5 
ABSTRACT.—The ‘Nest Protection Hypothesis' 
suggests that some birds add aromatic plants to their 
nests to repel or kill ectoparasites. This behavior has 
been described for several species, including the 
Eurasian Blue Tit (Cyanistes caeruleus). We studied 
the reproductive performance, based on 26 nests (in 
nest boxes), of this species in mixed forested areas of 
Quercus spp, and Pinas pinea in the Parque Florestal de 
Monsanto, the largest park of Lisbon, Portugal. The 
frequency of aromatic plants in nests was compared 
with frequency of these plants in the study area. The 
three most frequent aromatic plants (Dittrichia vi.scosa, 
Lavandula deniata, Calaininrha baetica) in nests were 
used more than expected from their availability in the 
study area. We could not reject the null hypothesis that 
nest survival rale is independent of the presence of 
aromatic plants in the nest. Received 17 .lime 2011. 
Accepted 17 September 2011. 
Some birds use fragments of fresh plants in their 
nests different from those used in nest cup construc¬ 
tion. For example, raptors include fragments of 
resinous conifers (Dvkstra et al. 2009) 
in their nests and passerines use herbaceous and 
shrubby species ("Wimberger 1984. Lambrechts and 
Dos Santos 2(XX)). These fragments tire incorporated 
into the nest cup (Ontiveros et al. 2007) and several 
hypotheses have been presented to explain ihis 
behavior (e.g.. Bahbura et al. 1995. Gw inner and 
Berger 2006, Mennerat et al. 2009b). The ‘Nest 
Protection Hypothesis' (NPH) seems to be the most 
plausible explanation for this behavior when the 
green material is aromatic. This hypothesis suggests 
that sprigs of aromatic plants are added to nests 
because of the presence of volatile secondary 
' Avenida 5 de Oulubro, 267 2 Dto 1600-035 Lisboa 
Portugal. 
“Laboratory ol Botany. Department of Biology. Univcr 
sity of Evora. 7002-554 Evora. Portugal. 
' Laboratory of Ornithology. Department of Biology, Univci 
stty of Evora. 7002-554 Evora. Portugal. 
4 Mediterranean Ecosystems and Landscapes Research 
Group Ins,nute of Mediterranean Agrieul.ural and Environ 
menu) Sciences, Ujlrvcrs.ty offivora, 7002-554 Evora, Portugal 
Corresponding author; e-mail: jrabaca@uevora pt 
chemical compounds (e.g., Wimberger 1984). name¬ 
ly terpenes (Camacho et al. 2000), to redtiCv 
ectoparasite loads. Clark and Mason (1988)explained 
that volatile compounds can affect ectoparasite 
feeding, even if numbers of ectoparasites in nests 
do not decrease with presence of aromatic plants. 
The NPH should be more relevant for hoic- 
nesting birds which may reuse the same cavil' 
for several breeding attempts, thus increasing the 
probability of detrimental ectoparasite attack--. This 
trail has been documented for European Starlings 
(Slttnuis vulgaris) (e.g.. Gwinnerand Berger 2005 1 
and Eurasian Blue Tits (Cyanistes caeruleus) (t, g- 
Lambrechts and Dos Santos 2000. Mennerat et al 
2009b). Female Eurasian Blue Tits, a few days 
before egg laying, start to add fresh aromatic plait 
material to their nest (Mennerat et al. 2009a) aDd 
continue this behavior throughout the reproductive 
cycle (Lambrechts and Dos Santos2000). 
Our objective was to examine if Eurasian Blue Tits 
nesting in nest boxes use aromatic plains in their nests 
more than would be expected according toavailabil 
ity of these plants in the study area and. if so. which 
species are used. An additional objective can be 
established if aromatic plants are better represented m 
nests than predicted, indicating a selective plan 1 
search: does the presence of aromatic planis in the 
nests influence Eurasian Blue Til nest survival rate 
METHODS 
Study Area .—The study was conducted m 
Parque Florestal de Monsanto. Lisbon. Portugu 1 
the largest park in the city with -900 ha. The 
park has extensive forested areas dominated bv 
Quercus spp. ( Q. robur. Q. saber. 0. cocrifeni. Q 
rotundifoUa. Q. faginea, and 0. pyrentdea). P llul ' 
pinea . P. balepensis . and Eucalyptus glohune 
Four Quercus spp. and Pinus pinea mixed stand' 
of —8 ha each were selected as study sites. 
placed 484 (121/stand) pine wood nest bov-' 
(chamber size: internal height x width X depth 
17 X 10.5 x 13.5 cm; entrance hole diameter ~ 
3.5 cm) attached to a branch with a hook or wire 
au'ay from hard substrate, 3 to 6 m above the 
