Formatos de animación

In many respects, the breeding biology of hooded parrots is typical of other Australian parrots (Fig. 5). Adjusted for hen mass, egg size, egg volume, clutch mass and incubation period conform to the usual patterns exhibited by other Australian parrots. However, nesting success for hooded parrots was high for the two breeding seasons in this study; 11% higher than that reported by Reed and Tidemann (1994) in their study of hooded parrots 25 years earlier and higher than has been found for many temperate Australian parrot species (appendix 1).

The nesting period in this study matched that found by Reed and Tidemann (1994) at the King River site. Hooded parrots start nesting in January, however most breeding activity occurs in February, before tapering off to be completed by the end of April. In March of both years, high rainfalls coincided with a cessation of clutch initiation. In 2006 these rains continued and no further nests were found in these breeding seasons, however in 2007, three further nests were initiated once the heavy rain stopped. The greatest food abundance for hooded parrots occurs near the end of the wet season (around April-May; Woinarski and Tidemann 1991; Garnett and Crowley 1995), which coincides with the fledging of chicks and peak demand for food by hooded parrots.

In 2006, hooded parrots nested earlier, the chicks were bigger and nests were more successful than in 2007, which suggests that 2006 was a better, albeit shorter, breeding season. This may reflect the weather during the two seasons in which the study was conducted. Both seasons studied had extended dry periods in the middle of the wet season, however the dry period was more pronounced in 2006 than in 2007 (February rainfall for Katherine Aviation Museum, 14.44°S 132.27°E: 2006 62 mm; 2007 97.7 mm; 65 year average 239.8 mm; Bureau of Meteorology 2008). The extended dry period in 2006 may have promoted seed set in annual grasses earlier in the wet season, and therefore earlier in the breeding cycle of the parrot. The increased availability of food for parrots earlier in the nesting period may therefore have resulted in better nesting conditions in 2006 compared to 2007.

Nests that were initiated earlier in the season were able to fledge their chicks at a younger age and the chicks were bigger and heavier than those in later nests,

Hooded parrot breeding biology _● Discussion | 24

although there was no difference in the wing length. This suggests that the use of energy to grow wings is constant, regardless of all but the most severe food shortage, and that the delays in fledging experienced by later broods are caused by shortages of food that result in these chicks fledging lighter and smaller.

The hooded parrot is one of three ‘antbed’ parrots, so named because of their habit of nesting in termite mounds. Almost nothing is known about the breeding biology of the extinct paradise parrot, however the golden-shouldered parrot has been studied extensively (see Crowley et al. 2004). Hooded parrots have been regarded as analogues for golden-shouldered parrots, especially in the ongoing management of golden-shouldered parrot populations (Garnett and Crowley 1995). Hooded parrots have smaller clutches than golden-shouldered parrots (4.5 vs. 5.5), but bigger eggs (21.8 mm x 18.7 mm vs. 20.6 mm x 17.8 mm; Higgins 1999), most likely as a result of their greater size. Hooded parrots, perhaps as a result of the bigger eggs, grow more quickly than golden-shouldered parrots and may fledge at a younger age (29 days for hooded parrots this study vs. 35 days for golden-shouldered parrots in Higgins 1999). However, accounts from captive birds record similar fledging ages for both species (Sindel and Gill 1996), suggesting that wild birds may fledge earlier.

In the hooded parrot population studied, reproductive losses were assumed to be the result of predation in the majority of cases, although no predator was seen taking chicks or eggs. In most cases the nest was left intact after the disappearance of the chicks, ruling out large goannas Varanus sp. (Crowley et al. 2004), however one nest was completely destroyed between visits and the chicks removed. There were three cases of apparent starvation. In one instance the condition of a chick declined after the loss of its siblings, before it too disappeared, and twice chicks were found dead in the nest. At one further nest, the hen was found dead in the nest and the eggs that were present on the previous visit had disappeared. Pied butcherbirds were assumed to be the main predators of hooded parrots and were abundant at the field sites, however these birds weigh close to 120 g (Higgins et al. 2006), more than twice the mass of adult hooded parrots (Higgins 1999) and it is not certain that they can gain access to the nest cavity. Conversely, at a cavity in one termite mound, a common tree snake

(Dendrelaphis punctulata)was found, although it was not known if this had been an active hooded parrot nest.

In birds, the sex ratio is typically close to parity (Clutton-Brock 1986). However, recent molecular techniques are revealing more cases of a biased sex- ratio in different species and under different conditions (Gowaty 1991; Heinsohn et al. 1997; Sheldon 1998). Parrots have been reported to manipulate the sex ratio of nestlings in response to nesting conditions (Heinsohn et al. 1997; Krebs et al. 2002; but see Budden and Beissinger 2004). Further, biased sex ratios are more common is sexually dimorphic birds (Clutton-Brock 1986) such as the hooded parrot, therefore it is possible that they are candidates for this behaviour. Indeed, in captivity one pair of parrots had extremely biased clutches resulting in 17 of 18 birds being male, before the following year producing seven out of eight female chicks (Sindel and Gill 1996). Despite this, no evidence of sex ratios that were significantly different to parity was found over the course of this short study.

This study adds to the growing literature about the breeding biology of tropical birds and in particular tropical parrots. With the decline of many species of parrot, information such as presented here will enable land and wildlife managers to make better informed decisions about hooded parrots so that the chances of them suffering the same fate as their congeners is lessened.

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CHAPTER III