Thank you Julie, that is very helpful!

I have been thinking about this question and I figured out based on the paper attached to my Researchgate page that birds like fish can feed on small fruit as Cecropia pachystachya Trec. Cecropiaceae (Pilati et. al. 1997), and thus most of the seeds are eliminated after passing throughout the digestive tract. The influence on the seed quality is possible to see in my paper “Testing the physiological quality of seed lots” attached to the same page on August, 2016. I have had experience with birds species eliminating small seeds on the roof and door handle of my car when it is parked in front of my laboratory in the Iguatemi Research Farm. Furthermore, two weeks later I photographed about five species of birds eating papaya and banana. Papaya is dispersed in my own land as well as cactus (Cereus peruvianus). I do not believe that mature seed choice has been the main option to birds. Best regards.

Thanks Jose!

I also could not think of any evidence that frugivorous birds can detect seed viability, and really cannot foresee a benefit for the bird, since the seed will be excreted or regurgitated. However, on the plant side we could certainly expect strong evolutionary pressure for the fruit to be most attractive to the bird at the optimal time for seed viability.

I have noticed our frugivorous birds (n-e Australia) will pick out only a few fruits among many that look ripe to my eyes. It seems these birds discriminate very finely on the maturity of fruit and presumably they select the degree of ripeness that provides greatest nutritonal value for the bird. How they detect the 'exactly-right' stage might be complex - not colour alone perhaps.. For some plant species there are reports that chemical defences in the fruits correspond to visual appearance of ripeness e.g. deterrent chemicals present in unripe fruit will disappate when the fruit is 'ready' to be eaten and dispersed - from the plant side 'ready' would imply at least the seed must be sufficiently developed to be viable..

Thanks Julia!

Andrew,

In this papers I guess you can find the kind of information your are required

http://ebd06.ebd.csic.es/personal/cmh/cmh.Publs.todas.html

In this link you can download it .

Herrera, C. M. (1981) Fruit variation and competition for dispersers in natural populations Herrera, C. M. 1981. Fruit variation and competition for dispersers in natural populations

of Smilax aspera. - Oikos 36: 51-58.

The berries of Sm'Zux aspera L. (Liliaceae), a woody climber of mediterranean scrub,

may have either one, two or three seeds. One-seed fruits have the largest, and

three-seed the smallest, pulpiseed ratio, so differently-seeded fruits have a differential

feeding value to birds feeding on them. In Andalusia, southern Spain, the overall

proportions of fruits with different seed number was found to vary between populations

as well as between individuals of the same population. S. aspera fruiting season

overlaps extensively with the fruiting period of many other species and all of them

share the same few species of bird dispersers. It was then hypothesized that interpopulation

variation in fruit seed numbers was related to interspecific competition

among plants for dispersers. To test this hypothesis, twelve populations of S. aspera

were sampled for fipe fruits. For each sample, the proportions of one-, two- and

three-seed fruits were determined, and a set of environmental variables was recorded

at each sampling locaiity. Multiple stepwise regression analysis shows that the best

single predictor of the mean number of seeds per fruit is the number of plant species

bearing fruits simultaneously and equally or more abundant than S. aspera. Assuming

that the intensity of competition among plant species for dispersers must be roughly

proportional to the number and population sizes of competitor species, these results

suggest that inter-population variation in the number of seeds per fruit is actually

related to variation in competitive pressures, provided that 1) dispersers are in short

supply, 2) dispersers select to some extent the most profitable fruits, and 3) number

of seeds has some genetic component. Evidence supporting these three assumptions

is presented, thus suggesting that observed variation in fruit seed numbers must be

attributed to interspecific competition for dispersers among plants.

C. M. Herrera, Estacion Biologics de Doriana, SeviIla - 12, Andalucia, Spain.of Smilax aspera. Oikos 36, 51-58.

Thanks Ramon!

Scatter-hoarding birds definitely select for viable fruit. Check out our review paper on corvid scatter-hoarding as seed dispersal