Alfred M. Dufty

Vocal communication in the domestic chicken: I. Does a sender communicate information about the quality of a food referent to a receiver?

Abstract Male domestic chickens produce ‘food calls’, when they are presented with food. Experiments, conducted under controlled conditions, on the responses of cockerels to the presentation of various foods in the presence of a hen indicate that the rates and numbers of food calls vary with the preference ranking of the food. A hen is more likely to approach a male when he is calling than when he is silent. The probability of a hen approaching is greater when the male is calling to a highly preferred food than to a low-preference food. We conclude that male food calling communicates information about food quality to a female chicken, the signal receiver.

Vocal communication in the domestic chicken: II. Is a sender sensitive to the presence and nature of a receiver?

Abstract As a test of the automaticity of the food calling behaviour of cockerels, their sensitivity to the presence and nature of an audience was explored. Males were presented with either a highly preferred food or a non-food item in the presence of a familiar female, a strange female, a male, or with no audience at all. With food as a referent, there was significantly less food calling with no audience than in the presence of females, and even less with a male as a potential receiver. There was a significant amount of calling for the non-food item, especially in the presence of a strange female. Food calling to non-foods in certain social contexts is discussed as a case of deception. The modulation of signal production according to the nature of the receiver is considered in relation to the issue of intentionality in animal communication.

The influence of social cues on the reproductive endocrinology of male brown-headed cowbirds: field and laboratory studies.

Captive male brown-headed cowbirds exposed to long days exhibit gonadal growth and have elevated plasma testosterone (T) levels. This photoperiodic response is enhanced if males are housed with female cowbirds: Photostimulated males with females increase plasma testosterone levels sooner than do individually housed photostimulated males. Peak plasma T levels are similar in both groups, although peak levels are maintained longer in males housed with females. The gonadal cycle is similarly affected; males in the presence of females have earlier gonadal recrudescence and maintain mature gonads longer than do photostimulated males without females. Plasma corticosterone levels increase in the unpaired males, suggesting that removal of social cues is stressful for these birds. Free-living paired males have significantly higher plasma testosterone levels than do unpaired/unknown males early in the season, when social relationships are being established; the levels are similar thereafter. There is no difference between the two groups in testicular maturation rates; nor do they differ in plasma corticosterone levels at any time of the season. These results suggest that social stimuli are important in modulating the secretion of testosterone in males early in the season when pairing occurs, and possibly late in the season as well, probably to prevent termination of breeding prior to that of females.

Corticosterone and the Stress Response in Young Western Screech-Owls: Effects of Captivity, Gender, and Activity Period

We used a standard handling protocol to examine the stress response of captive young western screech-owls during their active (nighttime) and inactive (daytime) periods and to compare the stress responses of captive and free-living owls. Circulating corticosterone levels were significantly higher during the inactive period than in the active period in this nocturnal species. This suggests that the daily pattern of corticosterone secretion is reversed in nocturnal birds and is correlated with activity period rather than with the light/dark cycle. Young (ca. 4-5 mo old) screech-owls of both sexes showed increases in plasma corticosterone up to 30 min after capture, followed by significant decreases at 60 min. This pattern is similar to those of other species of birds examined previously, except that decreases in corticosterone at 60 min rarely have been observed. Such decreases may be the result of physiological differences between adult and young birds, habituation to handling in captive birds, or the effects of body condition. Corticosterone levels and the response to capture and handling were comparable in captive and free-living owls, which suggests that the captive owls were not subjected to chronically high levels of stress.

Identity of gonadotropin-releasing hormone in passerine birds: Comparison of GnRH in song sparrow (Melospiza melodia) and starling (Sturnus vulgaris) with five vertebrate GnRHs

Gonadotropin-releasing hormone (GnRH) was detected in the brains of passerine birds, a recently evolved and diverse avian group. The molecular forms of GnRH in two species of birds under breeding conditions were deduced using methods of HPLC and immunology. The brain extracts of song sparrows (Melospiza melodia) contained a form of GnRH identified as chicken I GnRH-like peptide by its HPLC elution pattern and cross-reactivity with four antisera. In contrast, starling (Sturnus vulgaris) brain extracts showed molecular heterogeneity of GnRH forms; equal amounts of chicken I and chicken II GnRH-like peptides were present. Neither bird contained GnRH that could be identified as mammalian, salmon, or lamprey GnRH. Chicken II GnRH-like peptide may not have evolved after the separation of the song sparrow and starling as both peptides are found in chicken, a more primitive bird. The possibility remains that different stages of the life cycle are associated with the expression of these GnRH-like peptides or their ratio. Only determination of the primary structure will establish whether our chromatographic and immunological evidence is correct that chicken I and II GnRH are present in passerine birds and have been conserved in representatives throughout the reptiles and birds. Starlings can be added now to the growing list of submammalian species that express multiple forms of GnRH in their brains.

NEST BOX TEMPERATURE AND HATCHING SUCCESS OF AMERICAN KESTRELS VARIES WITH NEST BOX ORIENTATION

Abstract We studied orientation-dependent differences in nest box microclimate and American Kestrel (Falco sparverius) reproductive parameters in Idaho, USA. Unoccupied nest boxes facing west were ∼0.6° C cooler than boxes that faced south or east and had ∼20% lower relative humidity levels than boxes facing all other cardinal directions. Clutches in occupied boxes that faced southwest had a proportionately lower chance of hatching success (12 of 21 nests were successful), defined as having at least one egg hatch, than boxes that faced northwest (9 of 9 nests) or southeast (9 of 12 nests). The possible link between orientation-dependent differences in microclimate and hatching success, and the question of whether American Kestrels may select for orientation adaptively requires further investigation.

NESTLING IMMUNOCOMPETENCE IS AFFECTED BY CAPTIVITY BUT NOT INVESTIGATOR HANDLING

Abstract Environmental conditions during the neonatal period can affect the growth, physiology, behavior, and immune function of birds. In many avian studies the nestling environment includes investigator handling of young, which may be stressful. While neonatal handling is known to affect the adult phenotype in rats, the effects of handling on development have rarely been examined in wild birds. We examined the effect of short, repeated periods of neonatal handling on avian growth and immune system development. We subjected American Kestrels (Falco sparverius) and European Starlings (Sturnus vulgaris) to 15 min of daily investigator handling throughout the nestling period, while controls remained undisturbed. Immediately prior to fledging we assessed cutaneous immunity, humoral immunity, mass, and degree of fluctuating asymmetry. Daily handling did not significantly affect any of these measurements. We also addressed the possibility that treatment differences would appear only when birds were challenged with a more substantial stressor by bringing birds into captivity for 24 hr. Captivity did not affect mass, but significantly lowered the cutaneous immune response, although this was independent of treatment. Therefore, brief periods of investigator handling did not appear to affect immune or morphological development in these species, whereas 24 hr of captivity resulted in suppressed cutaneous immune responses.

Rejection of Foreign Eggs by Yellow-Headed Blackbirds

Egg rejection behavior is more likely to develop in avian populations that experience high levels of heterospecific brood parasitism than in populations where parasitism exerts little selection pressure to recognize and respond to foreign eggs (Davies and Brooke 1989, Brown et al. 1990, Soler and Moller 1990 [but see Zufiiga and Redondo 1992], Briskie et al. 1992). Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) are not preferred hosts of the brood-parasitic Brownheaded Cowbird (Molothrus ater; hereafter cowbird) and rarely are parasitized (Willson 1966, Ortega and Cruz 1988, Neudorf and Sealy 1994 [Table 1], L. Beletsky and G. Orians, pers. comm.; but see Lincoln 1920). Consequently, low rates of heterospecific brood parasitism exert little selection pressure on Yellow-headed Blackbirds to recognize parasitic eggs, and individuals from populations with low parasitism rates do not reject nonmimetic eggs placed in their nests (Ortega and Cruz 1988). However, if a population of Yellow-headed Blackbirds were to experience significant amounts of brood parasitism, then one might expect to see evidence of egg rejection. I investigated this hypothesis in a population of this species that is heavily parasitized (1991: 7/33 nests [21.2%]; 1992: 5/29 nests [17.2%]) by cowbirds (Dufty, in prep.). I noted responses to the presence of foreign eggs by replacing single eggs in Yellow-headed Blackbird nests with an egg of the Red-winged Blackbird (Agelaius phoeniceus).

Endocrine Response of Captive Male Brown-Headed Cowbirds to Intrasexual Social Cues

The hormonal response to a spectrum of intrasexual social stimuli was studied in captive Brown-headed Cowbirds (Molothrus ater). Males were housed in individual cages in one of four conditions: (1) in a semicircle with other males (= visual + vocal stimuli), (2) in acoustic chambers with visual access to a devocalized companion (= visual stimuli only), (3) in chambers in which a tutor tape was played daily (= vocal stimuli only), and (4) in acoustic chambers with no other input (neither visual nor social stimuli). Blood samples were taken at 2-week intervals throughout the spring and early summer and assayed for testosterone. The results indicate that the greatest increase in testosterone was in the birds receiving visual plus vocal stimuli and in those receiving only visual stimuli; males receiving only vocal stimuli had a muted endocrine response, and those receiving no social stimulation exhibited the briefest response. The relatively small response to vocal stimulation is consistent with the absence of a behavioral response to simulated territorial intrusions (i.e., song playbacks) that has been shown in previous studies in male cowbirds.

Vocal and behavioral responses of brown-headed cowbirds to flight whistles from different dialects

We examined the vocal and behavioral responses of free-living male Brown-headed Cowbirds (Molothrus ater) to playbacks of flight whistles (FWs) from local, near-foreign, and distant-foreign dialects. Full, partial, and reverse FWs were broadcast to solitary males. Test males responded with their own FWs and approached playbacks of FWs significantly more than playbacks of control heterospecific vocalizations. This suggests that all three dialects were recognized as conspecific. The strongest responses were elicited by playbacks of local FWs, and there was little behavioral evidence that males distinguished between the near-foreign and distant-foreign dialects. Males responded to playbacks of partial or complete local FWs primarily with the next or missing part of the FW. That is, they avoided matching the playback. The FW responses to playbacks of near-foreign anti distant-foreign FWs were not consistent. Males presumably use matching-avoidance within a FW dialect to initiate social interactions with particular conspecific males.