[R] fisher.alpha warnings

[Kulupp]

I have two vectors (a and b) with counts of animals and wanted to 
calculate fisher's alpha:

library(vegan)
a <- c(2043, 1258, 52, 1867, 107, 1624, 2, 157, 210, 402, 5, 107, 267, 
2, 13683)
b <- c(2043, 1258, 52, 1867, 107, 1624, 2, 157, 210, 402, 5, 107, 267, 
2, 3000)
fisher.alpha(a)
fisher.alpha(b)

fisher.alpha(a) gave the following warnings:

 > fisher.alpha(a)
[1] 1.572964
Warnmeldungen:
1: In log(p) : NaNs wurden erzeugt
2: In log(1 - x) : NaNs wurden erzeugt
3: In nlm(Dev.logseries, n.r = n.r, p = p, N = N, hessian = TRUE, ...) :
   NA/Inf durch größte positive Zahl ersetzt

fisher.alpha(b) gave no warnings (note: only the last number in the 
vector 'b' differs from 'a'!)

Why did vector 'a' gave warnings and what does that mean for the 
validity of the calculated alpha-value?