Elsevier

Behavioural Processes

Volume 56, Issue 2, 1 November 2001, Pages 113-120
Behavioural Processes

Aromatic plants in bird nests as a protection against blood-sucking flying insects?

https://doi.org/10.1016/S0376-6357(01)00191-7Get rights and content

Abstract

The nest protection hypothesis suggests that some of the fresh plant material, brought by some bird species to their nests, contain secondary compounds that repel parasites or mask the chemical cues that parasites use to find the host. Corsican blue tits (Parus caeruleus) bring pieces of several species of aromatic plants to the nest at dusk, suggesting a protection against nocturnal agents such as blood-sucking flying insects. The potential repellent or masking effect of these aromatic plant species, alone or in mixture, was experimentally investigated in the mosquito Culex pipiens, using domestic chicks as bird hosts. Aromatic plants had a repellent effect against mosquitoes, although a masking effect could not be ruled out. The plant mixture was the most efficient, although some aromatic plants had a significant effect when used individually. These results are discussed in the context of the nest-protection hypothesis and of the impact of flying blood-sucking insects on bird behaviour and life history traits.

Introduction

Animals use different defence mechanisms against parasites such as complex immune systems, resistance genes or specific behaviours (Loye and Zuk, 1991, Clayton and Moore, 1997). One of these mechanisms is self-medication, i.e. a defence against parasites by using substances produced by other organisms (Clayton and Wolfe, 1993). In some bird species, individuals bring green plant material to active nests that contain eggs or nestlings (Wimberger, 1984, Clark and Mason, 1985, Rodgers et al., 1988). Clark (1991) has reviewed the various functional hypotheses to explain this behaviour. The nest-protection hypothesis suggests that some of the fresh plants brought to the nest contain secondary compounds that repel parasites or mask the chemical cues that parasites use to find the host (Wimberger, 1984, Clark, 1991). This hypothesis provides the simplest explanation for why female Corsican blue tits (Parus caeruleus ogliastrae) incorporate into nests with eggs or nestlings, up to five aromatic herb species with distinct odours easily perceived by humans (Lambrechts and Dos Santos, 2000, Banbura et al., 1995). The plants selected represent a small fraction of the species observed in the blue tit territory. Furthermore, blue tits sometimes incorporate into the nest, fragments of plant species not observed in the territory (Lambrechts and Dos Santos, 2000, Petit, 2000). Lambrechts and Dos Santos (2000), therefore, hypothesised that a mixture of plants (the ‘Potpourri effect’) provides more benefits than the presence of a single plant species in the nest; for instance, treatment with a mixture of aromatic plant fragments would be a more efficient defence mechanism against parasites than the treatment with a single plant species (the ‘Potpourri hypothesis’).

Fresh plant material brought to the nest at the end of the evening, as observed in Corsican blue tits (Banbura et al., 1995), may be a defence mechanism against blood-feeding insects at night or dusk, such as ornithophilic mosquitoes (Rothschild and Clay, 1953, Jaenson, 1990). Although host–parasite interactions have been studied extensively in natural bird populations, the effects of blood-sucking flying insects on bird life history traits and behaviour are a neglected subject (Bucher, 1988, Loye and Carroll, 1995). This is probably explained by the relative discretion (nocturnal activity, ephemeral at the nest and small size) of these insects, which are essentially nematocera diptera: black flies (Simulidae), biting midges (Ceratopogonidae) and mosquitoes (Culicidae) (Rothschild and Clay, 1953). However, the insects are probably detrimental to their host by removing some blood, although they also inject toxins and may act as vectors of parasitic diseases (Scott and Edman, 1991, Richner et al., 1995). Some studies indicate that these effects can dramatically affect some life history traits (Anderson et al., 1999), particularly when bites are numerous (e.g. Smith et al., 1998). In northern Europe, 20 species of mosquitoes have been found to feed preferentially or occasionally on birds (Jaenson, 1990), and some viruses such as the sindbis virus (Togaviridae: Alphavirus) or the Nile virus (Flaviviviridae: Flavivirus) are equally found in birds and mosquitoes (Francy et al., 1989, Lundström et al., 1992, Anderson et al., 1999).

The aim of this study was to establish whether aromatic herb species found in Corsican blue tit nests repel blood-sucking flying insects or mask the presence of a host. Experiments were performed using the mosquito Culex pipiens (L.) (Diptera: Culicidae), which is common in Corsica (Raymond and Marquine, 1994) and can be a vector of avian malaria (Vinogradova, 2000). More specifically, experiments have been conducted with this mosquito presented to a bird host in laboratory conditions, with or without a mixture of the Corsican aromatic herb species. For practical reasons, domestic chicks (Gallus gallus) have been used in the experiments, instead of blue tits.

Section snippets

Plants

Four species of aromatic plants found in Corsican nests (Lambrechts and Dos Santos, 2000) were used: Achillea ligustica, Helichrysum italicum, Lavandula stoechas and Cistus creticus. For each experiment, 1 g of fresh material was used which is slightly above the mean, although within the range of natural variation of quantity (Lambrechts, unpublished data), containing either only one plant species or a mixture of all four, depending on the treatment: control (T1), mixture (T2); monospecific

Repellent experiment

Overall, the mixture of aromatic plants had a repellent effect (P<0.01, Table 1). Individual plants had no repellent effect, with the exception of L. stoechas (P<0.0001). Results were heterogeneous for the mixture and L. stoechas, not all repetitions showing a repellent effect (Table 1).

Choice experiment

The mixture of aromatic herbs had a highly significant effect (P<0.0001) to protect chicks from female seeking a blood meal (Table 2). The corresponding minimal probability (pmin) of blood feeding in the control

Discussion

Many birds select fresh plant material that they bring to the nest (Wimberger, 1984, Clark and Mason, 1985, Rodgers et al., 1988, Milton and Dean, 1999). Several studies have investigated the potential anti-ectoparasite or anti-pathogen effect of these fresh plants (Clark and Mason, 1985, Clark and Mason, 1988, Hart, 1997), mainly because they have volatile compounds often considered to have possible repellent or toxic properties against insects, bacteria or herbivores (Jacobson, 1990, Barel et

Acknowledgements

We thank F. Rousset for providing the binomial exact test program, C. Bernard, M. Marquine, P. Perret, A. Dos Santos for technical assistance and C. Berticat, C. Chevillon, D. Heyse, C. Manus for help in mosquito supply, M. Hossaert-McKey for comments. This is contribution no. ISEM 2001.083 (UMR 5554).

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