The ratio of brain size to body size (relative brain size) is often used as a measure of relative investment in the brain in ecological and evolutionary studies on a wide range of animal groups. In birds, a variety of methods have been used to measure the brain size part of this ratio, including endocranial volume, fixed brain mass, and fresh brain mass. It is still unclear, however, whether these methods yield the same results. Using data obtained from fresh corpses and from published sources, this study shows that endocranial volume, mass of fixed brain tissue, and fresh mass provide equivalent estimations of brain size for 48 bird families, in 19 orders. We found, however, that the various methods yield significantly different brain size estimates for hummingbirds (Trochilidae). For hummingbirds, fixed brain mass tends to underestimate brain size due to reduced tissue density, whereas endocranial volume overestimates brain size because it includes a larger volume than that occupied by the brain.
Brain Behav Evol

中文翻译：

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不同的方法对鸟类大脑大小的估计结果是否相同？

在对各种动物群体的生态和进化研究中，大脑大小与身体大小的比率（相对大脑大小）通常被用作衡量大脑相对投资的指标。在鸟类中，已使用多种方法来测量该比率的大脑大小部分，包括颅内体积、固定脑质量和新鲜脑质量。然而，目前尚不清楚这些方法是否产生相同的结果。使用从新鲜尸体和已发表来源获得的数据，这项研究表明，颅内体积、固定脑组织的质量和新鲜质量为 19 个订单的 48 个鸟类家族提供了等效的大脑大小估计。然而，我们发现，各种方法对蜂鸟（Trochilidae）的大脑大小估计产生显着差异。对于蜂鸟来说，
大脑行为进化