Male Domestic Chicks Research Articles

Increased exposure to yolk testosterone has feminizing effects in chickens, Gallus gallus domesticus

Competing for food by altricial and semiprecocial bird nestlings is a behaviour well known for its sensitivity to maternal androgens during prenatal development. Whether a similar effect is present in precocial species that do not beg is less well known. We therefore increased yolk testosterone levels within the physiological range at the onset of incubation to study its effects on food competition behaviour in the domestic chicken, Gallus gallus domesticus. We found an increase in competitiveness in testosterone-treated male domestic chicks, raising their level to that of the females. This is in line with the decrease in circulating plasma levels of males in the direction of the levels in females, and the overall decrease in androgen receptor densities after prenatal treatment as found previously. Hormones are known to have long-lasting organizing effects on behaviour and to affect sexual differentiation in vertebrates. Although research into hormone-mediated maternal effects has been productive, only a few studies describe (the ambiguous) effects into adulthood. Therefore we followed our animals into adulthood and recorded androgen-dependent social behaviour and secondary sexual characteristics, body mass and circulating plasma testosterone levels and checked whether these variables were treatment dependent. Treatment had a near significant effect on comb colour (both brightness and chroma). Again treatment caused a shift towards a more female-like phenotype. This suggests that, in contrast to earlier suggestions, maternal androgens may interact with (but not disrupt) sexual differentiation of brain and behaviour and the development of secondary sexual characteristics.

Monocular sleep in male domestic chicks

Behavioural sleep during the first 2 weeks after hatching was studied in male chicks reared with an imprinting object (I-chicks) and in social isolation (NI-chicks). Time spent in sleeping with both eyes closed (binocular sleep) decreased gradually with age in both I-chicks and in NI-chicks whilst the number of episodes of binocular sleep decreased with age in NI-chicks but not in I-chicks. The pattern of monocular sleep (only one eye closed) of both I-chicks and NI-chicks showed no significant bias towards predominant left- or right-eye closure during the first week. During the second week, I-chicks showed a tendency towards more pronounced left-eye closure with a peak on day 10, whilst NI-chicks showed a tendency for more pronounced right-eye closure with peaks on days 9 and 11. In a different group of chicks, changing the colour of the imprinting object on day 8 produced a shift towards right-eye closure. In contrast, the removal of the imprinting object on day 8 did not cause any change in the pattern of monocular sleep. Differences with respect to sleeping patterns previously observed in females chicks are discussed.

Selective associations in day-old chicks: When do CS traces become available for sickness-conditioned learning?

Barber and colleagues (T. A. Barber, A. M. Klunk, P. D. Howorth, M. F. Pearlman, & K. E. Patrick, 1998; T. A. Barber, M. F. Pearlman & K. E. Patrick, 1995) showed that male domestic chicks would not peck a bead presented 15 or more min before a lithium chloride (LiCl) injection, but would peck a bead presented less than 15 min before a LiCl injection. In 4 experiments, the authors (a) confirmed their initial observation, (b) showed that the effect is not due to retrograde amnesia produced by LiCl, and (c) confirmed that memories less than 15 min old are available for other types of learning.

Selective associations in day-old chicks: When do CS traces become available for sickness-conditioned learning?

Barber and colleagues (T. A. Barber, A. M. Klunk, P. D. Howorth, M. F. Pearlman, & K. E. Patrick, 1998; T. A. Barber, M. F. Pearlman & K. E. Patrick, 1995) showed that male domestic chicks would not peck a bead presented 15 or more min before a lithium chloride (LiCl) injection, but would peck a bead presented less than 15 min before a LiCl injection. In 4 experiments, the authors (a) confirmed their initial observation, (b) showed that the effect is not due to retrograde amnesia produced by LiCl, and (c) confirmed that memories less than 15 min old are available for other types of learning.

Packed cell volume of blood from male domestic chicks.

The packed cell volumes of blood from healthy chicks of domesticated fowl were required for studies on avian malaria and data were specially generated under standardised conditions. The mean packed erythrocyte volume for chicks 15 to 43 d old (34 males of two egg laying breeds) was 28.7% (range 23 to 39%). The 95% confidence limits for a single reading in a healthy chick were 24.6 to 32.9%. Therefore, a value of less than or equal to 24% is regarded as subnormal and a value of greater than or equal to 33% is regarded as supranormal when readings are taken to the nearest 1%.

Parasagittal hypothalamic knife cuts in male chicks: advancement of reproductive function and changes in plasma concentrations of luteinising hormone and androgen.

Advancement of reproductive function occurred in male domestic chicks after lateral hypothalamic deafferentation (bilateral knife cuts extending from the preoptic to the mamillary region) at 2 weeks of age. Five out of 24 chicks showed sexual precocity as shown by accelerated comb growth after surgery. The 5 chicks had significantly higher concentrations of plasma luteinising hormone (LH) and androgen (A) than 5 sham-operated controls. Maximum concentrations of plasma LH and A were observed 3 and 4 weeks respectively after surgery. It is concluded that in the male domestic chick gonadotropin secretion is inhibited by extrahypothalamic influences.

Enhancement of effectiveness of learning by testosterone in domestic chicks.

In young male domestic chicks, the presentation of a nonaversive colored bead to be pecked (pretraining) interfered with subsequent avoidance training, in which the bead presented tasted unpleasant, when two conditions were fulfilled: (a) Beads used at pretraining and training were of similar appearance, and (b) testosterone was injected either before or a little after pretraining. This effect of the hormone was not a consequence of changes in behavior at training or at test. It appeared to reflect changes during the consolidation of the pretraining memory trace which made it more effective in subsequent competition with training. Beads that are blue in color were unusual in evoking high levels of avoidance in naive chicks and, when used in pretraining in the presence of testosterone, in failing to oppose subsequent training on the blue bead. Such pretraining became effective when paired with avoidance training with a bead of different color, apparently by changing the information stored about pretraining.

Reactions of male domestic chicks to two-dimensional eye-like shapes

There is considerable evidence that eye-shapes are aversive to the domestic chick but controversy remains over the relative importance of various features of the eyes in causing aversion. In this study the potency of various eye-like shapes in causing avoidance was evaluated. It was shown that monochromatic, two-dimensional eye shapes elicit avoidance and fear in young male domestic chicks, and that the eye shapes are not responded to merely as conspicuous objects. Horizontal orientation, pairedness and the presence of both an ‘iris’ and a ‘pupil’ are important recognition cues. The shape of the eye-like stimulus appears to be more important than its size. Circularity of the iris is not an essential feature but further work is necessary before conclusions can be drawn regarding the shape of the pupil although the available evidence does suggest that circularity is important.

Open-field responses of domestic chicks in the presence or absence of familiar cues

Male domestic chicks were reared in groups with distinctive cues (red crosses) placed on the walls of the home boxes from 2 to 7 d of age and their subsequent behaviour in an open field in the presence or absence of the familiar rearing cues was recorded. Ambulation, peeping, pecking, jumping and standing were all significantly higher and the latency to the first step, duration of freezing, sitting time, lying time and time spent with the eyes closed were significantly lower when the familiar rearing cues were present in the test situation. These observations are consistent with the suggestion that the birds are less fearful in the presence of familiar stimuli. The presence of the familiar cues also increased the time spent feeding and drinking. The preference effect was a specific one, for birds exposed to red crosses in early life preferred such stimuli to black circles in a subsequent two-choice situation, whereas chicks reared with black circles preferred them to red crosses. There was no generalisation of attachment from one stimulus to the other. As the chicks spent more time feeding and drinking in the presence of the familiar cues, it is assumed that fear was reduced. Thus, the results tend to confirm that the frequency of certain behaviour patterns is indicative of certain levels of fear.