Although most birds do not seem to rely on chemical defense mechanisms, some species from the genus Pitohui and Ifrita in Papua New Guinea have been found to make use of toxins. These birds contain low amounts of batrachotoxins such as 37 in their skin and feathers. The birds are likely to sequester batrachotoxins from their food, because Melyrid beetles that are consumed by the birds have been recently identified as a rich source of these toxins. The occurrence of similar batrachotoxin-containing beetles in Colombian rain forests suggests that Phyllobates frogs also sequester the batrachotoxins. The amount of batrachotoxins, for example, 37 in Pitohui and Ifrita birds is sufficient to render them unpalatable for mammalian predators such as humans.
Birds often are victims of attack by bugs and ticks. Some birds have been observed to 'bath' in ant nests making use of ant secretions such as formic acid 2 to remove bugs. Interestingly, the analysis of volatile emissions from bird feathers of Aethia cristatella revealed the presence of aldehydes such as octanal and decanal which have been found to effectively repel and kill ticks.
Figure 10 (E)-2-Butene-1-thiol, one of the major components of the deterring odor of the skunk (Mephitis macroura).
antibodies that bind to the foreign molecular structures of the invading pathogen.
Interestingly, similar mechanisms to the mammalian innate immune system are now also being discussed for plants (see discussion on flagellin recognition in Plant Defense Strategies).
Yet, there are some mammals that use chemical defense strategies. For example, the skunk (Mephitis macroura) is famous for spraying extremely unpleasant volatiles from its anal gland when attacked. The compounds comprise a complex mixture of various mercaptanes such as (£)-2-butene-1-thiol 40 (Figure 10).
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