Protein Requirements of a Specialized Frugivore, Pesquet's Parrot (Psittrichas fulgidus)

Abstract

For those few bird species that are exclusively frugivorous, the low protein content of fruits is likely a major nutritional constraint. Physiological mechanisms that allow strict frugivory remain enigmatic, but reduced protein requirements may suffice. We investigated protein requirements of Pesquet's Parrot (Psittrichas fulgidus), a highly specialized, obligate frugivore. Three isocaloric, fruit-based diets of varying protein content (6.1, 3.3, and 2.6% dry mass crude protein) were used in feeding trials lasting three to five days per diet. A minimum dietary protein requirement of 3.2% dry mass was estimated from balance trials. Endogenous nitrogen losses were 0.05 gN kg−0.75 day−1 and nitrogen equilibrium occurred at 0.32 gN kg−0.75 day−1. Those values are extremely low compared to those of granivorous and omnivorous bird species, but higher than those of nectarivorous species. In terms of nitrogen losses and requirements, Pesquet's Parrot most closely parallels the highly frugivorous Cedar Waxwing (Bombycilla cedrorum). Thus, reduced protein requirements appear to play an important physiological role in ability of highly frugivorous birds to subsist on fruit diets.

Dietary specialization and fruit availability among frugivorous birds on Sulawesi

“…However, they are seed predators and derive valuable nutrition from digesting fig seeds (Lambert 1989). Therefore, only the Black-naped Fruit-dove might predominantly rely on the nutritional rewards of the flesh of fig fruits (and fig-wasp content, but this is considered negligible by Pryor et al 2001). Fruit-doves, however, have specialized physiological adaptations to facilitate obligate frugivory (Schleucher 2002).…”

Nutrients in fruits as determinants of resource tracking by birds

“…Frugivores may track fruits to increase their resource intake, selecting food on the basis of fruit quantity and quality (Loiselle & Blake 1991, Rey 1995, Vergara et al 2010. Although fruit is the primary source of food for some bird species in tropical forests (Pryor et al 2001, Snow 2004, Firth & Firth 2009), most fruit-eating birds consume (or temporally switch to) other food items such as insects, particularly in subtropical and temperate environments where seasonality is more pronounced and fruit availability becomes more variable or unpredictable (e.g. Izhaki & Safriel 1989, Levey & Karasov 1989, Carnicer et al 2008.…”

Protein requirements of three species of parrots with distinct dietary specializations

“…The feeding trials for the Pesquet's parrots were previously described in detail by Pryor et al [2001]. These experiments were conducted on 15-30 May 1997 at the Wildlife Conservation Society (WCS) Wildlife Survival Center on St. Catherines Island, Georgia.…”

“…However, some specialized frugivores can maintain body mass when fed exclusively fruits, at least for a short period [Berthold, 1976;Holthuijzen and Adkisson, 1984;Bairlein, 1987;Worthington, 1989;Izhaki, 1992;Witmer, 1998;Witmer and Van Soest, 1998]. Proposed physiological mechanisms that enable such specialists to deal with limited dietary protein include low endogenous protein losses, low protein requirements, and high food intake [Walsberg, 1975;Paton, 1982;Wolton et al, 1982;Herrera, 1984;Thomas, 1984;Bairlein, 1987;Karasov and Levey, 1990;Brice and Grau, 1991;Bosque and Parra, 1992;Izhaki, 1992;Jordano, 1992;Levey and Karasov, 1992;Levey and Karasov, 1994;Klasing, 1998;Witmer, 1998;Witmer and Van Soest, 1998;Pryor et al, 2001]. Although high protein digestibility might be an additional digestive mechanism that allows some birds to cope with low dietary protein, most studies have shown decreased protein digestibility in frugivorous birds [Izhaki, 1992;Jordano, 1992;Levey, 1993;Klasing, 1998].…”

“…To calculate minimum endogenous protein losses and protein requirements, N balance analyses were conducted [Robbins, 1983;Murphy, 1993;Pryor et al, 2001]. First, N excretion was plotted against N intake (''N balance'') to determine N All values for millet obtained from Watt and Merrill [1975], unless noted as analyzed.…”