Tawny
Frogmouth breeding success
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| An average brood size of two Tawny Frogmouth chicks |
I have
been monitoring the breeding success of Tawny Frogmouths Podargus strigoides in Canberra, Australia, for several years and
have found that the pattern is fairly constant. About half the breeding pairs
rear two young to fledging; a few rear three in any year and about a quarter
rear one chick. The proportion of pairs which fail to rear any chicks is about
24% on average over the years, ranging from 17 – 34% (Figure 1). I do not
disturb the birds to record clutch size, but it is known to range from 1-3.
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| Figure 1: The number of young reared per breeding pair of Tawny Frogmouths in 2006 - 2012. |
In
recent years I had thought that more birds were failing to rear young, but this
is just the impression gained as I have added more pairs to the study in the
past few years. Although I have been recording more failures, this has been in
proportion with larger sample sizes, there is no statistical difference (χ2
= 3.8, df = 6, P = 0.43). The main causes of failure, which are usually the loss of whole
clutches or broods, are predation by unknown species, but likely Brush-tailed
Possum or Brown Goshawk. One male was taken off the nest by a feral cat. A few
nests have been blown out of their trees by strong winds.
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| Figure 2: The number of Tawny Frogmouth pairs which failed to rear any young in any year is proportional c24%, to the number studied (r = 0.899, P = 0.003). |
Further
study will aim to determine whether there are any differences between the
breeding success of frogmouths in grassy woodland, dry sclerophyll forest or
suburban remnant woodland; or if there is any difference between years of drought
and high rainfall. Fortunately the study has already covered these criteria.
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| A male Tawny Frogmouth protects his chick |
