humans [109, 121, 122]. As a result, they tend to rely strongly on fruit color for
detection and selection [24, 26, 123] and have exerted substantial selection pressures
on fruit color [24, 26, 124].
It is a long-held notion that frugivorous birds tend not to rely on olfaction as
strongly as mammals [29, 39, 40, 51, 125]. Evidence supporting this notion has been
rather circumstantial and was based primarily on the relatively simple olfactory
anatomy of many birds, especially passerines [126–128], and the reports that, unlike
mammals, frugivorous birds do not sniff fruits before ingesting [125]. Bird-consumed fruits tend to emit lower amounts of VOCs [25] and change their scent
profiles in ripeness less than mammal-consumed sympatric species [39, 40, 51].
This parallels the pattern observed in the bird pollination syndrome: in contrast to
insect- and bat-pollinated flowers, bird-pollinated flowers tend to emit only scant
amounts of scent [32]. In addition to the high reliance on vision, it is thus often
assumed that frugivorous tend not to rely strongly on olfactory cues.
However, these notions should be taken with cause since it is possible that bird
reliance on olfaction is simply less visible to human observers. Several studies
demonstrated the ability of passerines to use chemical cues in various situations
[128–131]. Performance in olfactory sensitivity and discrimination capacity tests is
difficult to compare directly to other frugivores. The olfactory sensitivity of passerines is somewhat low but, in the range, relative to other birds and primates [128,
132]. In conditioning tests, blue tits (Cyanistes caeruleus) – a non-frugivorous
passerine – learn to identify lavender oil, but their performance is rather low
compared to, for example, primates [127, 133, 134].
Thus, the absence of evidence for reliance on fruit scent, along with the high
visual capacities of birds and the fact that they tend to feed on less olfactory
conspicuous fruits, indicates that frugivorous birds tend to rely less on fruit scent
for food detection or selection. Yet given the many functions olfaction plays in the
lives of many birds, including passerines [128], and the fact that non-frugivorous
birds possess excellent olfaction [135], it is well likely that future studies would
demonstrate that this notion is oversimplified.
3.1.4 Other Animals
As the primary agents of seed dispersal in most systems, bats, birds, and primates
have received most of the focus in the study of the interaction between frugivory,
sensory ecology, and seed dispersal. But other animals consume fruits and may use
fruit scent to detect or identify ripe fruits. Elephants possess an excellent olfactory
system [136, 137] which can be employed to find plant material [138], mate choice
[139], and even identify human ethnic groups which hunt them [140]. Balanites
wilsoniana, a species growing in continental Africa, is dispersed by elephants
[141, 142] and emits a strong scent rich in aliphatic esters (Nevo, Valenta,
Chapman, unpublished data), which the elephants are likely to use to find and
select fruit.
Although birds are the most important animal seed disperser in temperate regions,
some plant species receive dispersal services from mammals, many of them
17 Fruit Scent: Biochemistry, Ecological Function, and Evolution
413
detection and selection [24, 26, 123] and have exerted substantial selection pressures
on fruit color [24, 26, 124].
It is a long-held notion that frugivorous birds tend not to rely on olfaction as
strongly as mammals [29, 39, 40, 51, 125]. Evidence supporting this notion has been
rather circumstantial and was based primarily on the relatively simple olfactory
anatomy of many birds, especially passerines [126–128], and the reports that, unlike
mammals, frugivorous birds do not sniff fruits before ingesting [125]. Bird-consumed fruits tend to emit lower amounts of VOCs [25] and change their scent
profiles in ripeness less than mammal-consumed sympatric species [39, 40, 51].
This parallels the pattern observed in the bird pollination syndrome: in contrast to
insect- and bat-pollinated flowers, bird-pollinated flowers tend to emit only scant
amounts of scent [32]. In addition to the high reliance on vision, it is thus often
assumed that frugivorous tend not to rely strongly on olfactory cues.
However, these notions should be taken with cause since it is possible that bird
reliance on olfaction is simply less visible to human observers. Several studies
demonstrated the ability of passerines to use chemical cues in various situations
[128–131]. Performance in olfactory sensitivity and discrimination capacity tests is
difficult to compare directly to other frugivores. The olfactory sensitivity of passerines is somewhat low but, in the range, relative to other birds and primates [128,
132]. In conditioning tests, blue tits (Cyanistes caeruleus) – a non-frugivorous
passerine – learn to identify lavender oil, but their performance is rather low
compared to, for example, primates [127, 133, 134].
Thus, the absence of evidence for reliance on fruit scent, along with the high
visual capacities of birds and the fact that they tend to feed on less olfactory
conspicuous fruits, indicates that frugivorous birds tend to rely less on fruit scent
for food detection or selection. Yet given the many functions olfaction plays in the
lives of many birds, including passerines [128], and the fact that non-frugivorous
birds possess excellent olfaction [135], it is well likely that future studies would
demonstrate that this notion is oversimplified.
3.1.4 Other Animals
As the primary agents of seed dispersal in most systems, bats, birds, and primates
have received most of the focus in the study of the interaction between frugivory,
sensory ecology, and seed dispersal. But other animals consume fruits and may use
fruit scent to detect or identify ripe fruits. Elephants possess an excellent olfactory
system [136, 137] which can be employed to find plant material [138], mate choice
[139], and even identify human ethnic groups which hunt them [140]. Balanites
wilsoniana, a species growing in continental Africa, is dispersed by elephants
[141, 142] and emits a strong scent rich in aliphatic esters (Nevo, Valenta,
Chapman, unpublished data), which the elephants are likely to use to find and
select fruit.
Although birds are the most important animal seed disperser in temperate regions,
some plant species receive dispersal services from mammals, many of them
17 Fruit Scent: Biochemistry, Ecological Function, and Evolution
413