Interspecific Allometry of the Brain and Brain Regions in Parrots (Psittaciformes): Comparisons with Other Birds and Primates

Abstract

Despite significant progress in understanding the evolution of the mammalian brain, relatively little is known of the patterns of evolutionary change in the avian brain. In particular, statements regarding which avian taxa have relatively larger brains and brain regions are based on small sample sizes and statistical analyses are generally lacking. We tested whether psittaciforms (parrots, cockatoos and lorikeets) have larger brains and forebrains than other birds using both conventional and phylogenetically based methods. In addition, we compared the psittaciforms to primates to determine if cognitive similarities between the two groups were reflected by similarities in brain and telencephalic volumes. Overall, psittaciforms have relatively larger brains and telencephala than most other non-passerine orders. No significant difference in relative brain or telencephalic volume was detected between psittaciforms and passerines. Comparisons of other brain region sizes between psittaciforms and other birds, however, exhibited conflicting results depending upon whether body mass or a brain volume remainder (total brain volume – brain region volume) was used as a scaling variable. When compared to primates, psittaciforms possessed similar relative brain and telencephalic volumes. The only exception to this was that in some analyses psittaciforms had significantly larger telencephala than primates of similar brain volume. The results therefore provide empirical evidence for previous claims that psittaciforms possess relatively large brains and telencephala. Despite the variability in the results, it is clear that psittaciforms tend to possess large brains and telencephala relative to non-passerines and are similar to primates in this regard. Although it could be suggested that this reflects the advanced cognitive abilities of psittaciforms, similar studies performed in corvids and other avian taxa will be required before this claim can be made with any certainty.

The socioecology of Monk Parakeets: Insights into parrot social complexity

“…Both parrots and primates have similar relative brain volumes (Iwaniuk et al 2005), are long-lived (Austad and Fischer 1992, Munshi-South and Wilkinson 2006, Young et al 2012, have extended developmental periods Nelson 2003, Emery 2006), live in complex social groups (Dunbar andShultz 2007, Hobson et al 2013), and show evidence of advanced cognition (Iwaniuk et al 2005, Roth andDicke 2005). Parrots also share additional characteristics with humans, which display the highest social and cognitive complexity of any species (Wilson 1975, Herrmann et al 2007.…”

Variation in avian brain shape: relationship with size and orbital shape

“…1). Notably, even in a serial-sectioned brain, the boundaries of brain regions are difficult to delineate in some specimens (Boire & Baron, 1994;Iwaniuk et al 2005), and our definition was based on the appearance of the brain endocast. Hence, our definition of regional boundaries does not completely coincide with that of histological boundaries.…”

“…Hence, it is known that the brain with a larger telencephalon is highly encephalized (Iwaniuk et al 2005), a large telencephalon correlates with an increase in relative brain volume. Iwaniuk et al (2005) reported that psittaciforms and passerines whose telencephalon is significantly larger than that of other birds have a relatively smaller mesencephalon, optic tectum, cerebellum and myelencephalon than non-passerines. We clarified that the apparent size of the brain regions changes according to the degree of encephalization, and this finding corroborates the volumetric result of Iwaniuk et al (2005).…”

“…Many studies have explored the relationship between brain morphology and behavior or sensory capacity using morphometric approaches. Volumetric methods, which typically compare total with regional brain volumes (Portmann, 1946;Jerison, 1973;Boire & Baron, 1994;Iwaniuk et al 2005), and linear measurement methods have been used to describe the morphological characteristics of the avian brain (Cobb, 1960a;Ashwell & Scofield, 2008;Milner & Walsh, 2009;Ksepka et al 2012). Portmann (1946Portmann ( , 1947, Boire & Baron (1994) and Rehk€ amper et al (1991) concluded from volumetric and histological analyses that most of the variation in avian brain size is due to the size of the telencephalon.…”

Can you teach an old parrot new tricks? Cognitive development in wild kaka ( Nestor meridionalis )

“…As foraging innovation frequency has been linked with larger relative brain size [5,7,35,36], we investigated agerelated differences in innovative problem-solving abilities in a large-brained parrot species [37], the forest-dwelling kaka (Nestor meridionalis). Kaka are an especially interesting species for studying the effects of personality and ecology on innovative problem-solving skills as they are generalist, extractive foragers [38], characteristics thought to be associated with increased problem-solving success [39,40].…”