Physiology & Behavior, Vol. 66, No. 5, pp. 809–813, 1999 © 1999 Elsevier Science Inc. Printed in the USA. All rights reserved 0031-9384/99/$–see front matter PII S0031-9384(99)00018-9 809 Latency to Traverse a T-maze at 2 Days of Age and Later Adrenocortical Responses to an Acute Stressor in Domestic Chicks RAUL H. MARIN* AND R. BRYAN JONES† 1 *Centro Regional de Investigaciones Científicas y Transferencia Tecnológica (CONICET) Mendoza y Entre Ríos, 5301 Anillaco, La Rioja, Argentina, and †Division of Environment and Welfare, Roslin Institute (Edinburgh), Roslin, Midlothian EH25 9PS, UK Received 30 November 1998; Accepted 19 January 1999 MARIN, R. H. AND R. B. JONES. Latency to traverse a T-maze at 2 days of age and later adrenocortical responses to an acute stressor in domestic chicks. PHYSIOL BEHAV 66(5) 809–813, 1999.—Latencies to escape from a T-maze, and thereby reinstate visual contact with conspecifics, were measured in broiler chicks at 2 days of age. Chicks were assigned to high- (HP) or low- (LP) performance categories if their escape latencies fell below 25 s or above 75 s, respectively. These chicks were then housed socially in 10 same-category groups (5 HP, 5 LP), each comprising eight birds. At 15 days of age, one chick was taken from each of two randomly selected cages (1 HP, 1 LP) and immediately bled (undisturbed controls). At the same time, another chick was taken from each of these boxes and immersed up to its neck in warm water (partial water immersion, PWI) for 15 min before blood was collected. All chicks were sexed after bleeding. There were no differences between the plasma corticosterone (CS) levels of undisturbed (control) HP and LP chicks. Exposure to PWI significantly increased circulating CS levels, and this elevation was more pronounced in LP than in HP chicks. Male chicks also showed higher stress-induced adrenocortical responses than did females. The present findings suggest that the T-maze responses of young chicks might pre- dict their later adrenocortical responses to a known stressor. This relationship is discussed in terms of individual differences in fearfulness, ability to cope with challenge, and/or stress susceptibility. © 1999 Elsevier Science Inc. Domestic chick T-maze behavior Partial water immersion Plasma corticosterone Stress THE considerable variation that exists within, as well as be- tween, populations of poultry in behavioral characteristics provides the vehicle for selective breeding. Genetic selection is undoubtedly the quickest and most reliable method of pro- moting desirable characteristics and eliminating harmful ones (6,16). For example, selection programs based on simple be- havioral tests applied at early ages yielded significant and rapid divergence in underlying fearfulness and social motiva- tion in chickens and Japanese quail (9,10,17,20). Though not yet subjected to directional selection, substantial individual variation has also been reported in the time taken by broiler chicks to escape from a T-maze and to reestablish visual con- tact with conspecifics (24–27), indeed, the chicks fall into three clear categories. High-performance (HP) chicks traverse the maze in 25 s or less, medium performance chicks take 25–75 s to accomplish this, while low-performance (LP) chicks are those that fail to emerge from the T-maze in 75 s. T-maze test- ing is an intuitively stressful procedure because it involves sudden isolation as well as exposure to an unfamiliar environ- ment, both of which are considered to be potent fear elicitors (10,15,16). Interestingly, following exposure to an acute stres- sor (partial water immersion, PWI), HP chicks showed greater benzodiazepine/GABA receptor density than LP ones (24). This finding suggests differential susceptibility to stress. How- ever, the measure is controversial because exposure to a vari- ety of stressful stimuli has been reported to either increase, decrease, or to have no effect on this receptor complex in avian and mammalian species (5,14,29,31). Adrenocortical ac- tivation is probably one of the most commonly used physio- logical measures of stress, although this too has been the sub- 1 To whom requests for reprints should be addressed. E-mail: Bryan.Jones@BBSRC.AC.UK