Abstract: Common cuckoos (Cuculus canorus) are obligate brood parasites, laying eggs into nests of small songbirds. The cuckoo hatchling evicts all eggs and young from a nest, eliminating hosts' breeding success. Despite the consistently high costs of parasitism by common cuckoos, great reed warbler (Acrocephalus arundinaceus) hosts sometime accept and other times reject parasitic eggs. To explore the cognitive basis of this seemingly maladaptive variation in host responses, we documented differences in egg rejection rates within 1-day periods just before and during the egg-laying cycle across host nests. Hosts rejected cuckoo eggs at 28% of nests during the pre-egg-laying stage, but when cuckoos exchanged the first host egg with the parasite egg, rejections increased to 75%. Even later, when several host eggs remained in a nest after parasitism, rejection rate fell to 37.5%. Experimental parasitism with conspecific eggs on the first and second day of host laying showed a similar directional change in relative rejection rates, dropping from 35 to 0%. Mistakes in egg discrimination (ejection error and ejection cost) were observed mostly in the latter part of the laying cycle, mainly when nests contained 5-6 eggs. These correlational and experimental patterns of egg rejection support a cognitive process of egg discrimination through several shifts in hosts' optimal acceptance thresholds of foreign eggs. The results are also consistent with the evolution of foreign egg rejection in the context of nest-sanitation (i.e. the removal of foreign objects). Our results suggest that common cuckoo hosts may recognize more eggs than they reject. This implies that the experience of the host with one or more of its own eggs in the clutch is a key factor in rejecting parasite eggs by allowing inspection and learning about their own clutch.

Abstract: Pigeons were trained with a conditional discrimination task in three-key operant chambers. Choosing either the left or right key was followed by food according to combinations of three preceding events: (a) a houselight illumination condition (dark or light), (b) presence or absence of green flashes on the three keys, (c) a color (amber or blue) of the center sample key. With these 2&#502&#502 event combinations, eight types of correct trials were prepared: (1) dark&#77no flash&#77amber&#77LEFT, (2) dark&#77no flash&#77blue&#77RIGHT, (3) dark&#77flash&#77amber&#77RIGHT, (4) dark&#77flash&#77blue&#77LEFT, (5) light&#77no flash&#77amber&#77RIGHT, (6) light&#77no flash&#77blue&#77LEFT, (7) light&#77flash&#77amber&#77LEFT, and (8) light&#77flash&#77blue&#77RIGHT. Seven of these eight types were used for training of a given bird, and then the remaining trial type was presented as the test. If the birds had learned the conditional structure of the events (the hierarchical switching rule), they would have responded correctly to the test type. However, they chose the opposite side key, suggesting that they had learned cue configuration or multiple rules to solve the task.

Abstract: Parental care can be costly to a parent in terms of both time and energy invested in the young. In species with cuckoldry or brood parasitism not all of the young under a parent's care are necessarily offspring. In such cases, distinguishing between kin and non-kin, and investing only in the former (nepotism), can be advantageous. Bluegill sunfish ( Lepomis macrochirus) are characterized by paternal care and cuckoldry, and care-providing males appear to show nepotistic behaviours. Here, we investigated nestling recognition in bluegill, determining whether parental males can differentiate between young from their own nest (familiar and related) and young from non-neighbouring nests (unfamiliar and unrelated) using (1) visual and chemical cues, and (2) chemical cues only. In the first experiment, wild-caught parental males were presented with samples of eggs or fry (newly hatched eggs) collected from their own nest or a foreign nest and placed on opposite sides of an aquarium. The time these parental males spent associating with each sample, and their “pecking” behaviours (indicating cannibalism), were recorded. Parental males showed no preference between eggs from their own nest and eggs from a non-neighbouring nest, but they preferred to associate with fry from their own nest over foreign fry. There also was a positive relationship between male body size and the time spent associated with fry from their own nest. Parental males pecked at foreign fry more than 5 times as often as fry from their own nest, though this difference was not statistically significant. In the second experiment, fry that were collected from the nest of a wild-caught parental male or a non-neighbouring nest were placed in different containers and the water from each was dripped into opposite ends of an aquarium. The time the male spent on each side was recorded. In this case, parental males spent more time near the source of water conditioned by unrelated fry, but there was a positive relationship between male condition (fat reserves) and the time he spent near the source of water conditioned by fry from his own nest. Results confirm that chemicals cue nestling recognition by parental male bluegill.

Abstract: Cotton top tamarins were tested in visible and invisible displacement tasks in a method similar to that used elsewhere to test squirrel monkeys and orangutans. All subjects performed at levels significantly above chance on visible ( n=8) and invisible ( n=7) displacements, wherein the tasks included tests of the perseverance error, tests of memory in double and triple displacements, and “catch” trials that tested for the use of the experimenter's hand as a cue for the correct cup. Performance on all nine tasks was significantly higher than chance level selection of cups, and tasks using visible displacements generated more accurate performance than tasks using invisible displacements. Performance was not accounted for by a practice effect based on exposure to successive tasks. Results suggest that tamarins possess stage 6 object permanence capabilities, and that in a situation involving brief exposure to tasks and foraging opportunities, tracking objects' movements and responding more flexibly are abilities expressed readily by the tamarins.

Abstract: Abstract  Encounters between groups of wild chacma baboons (Papio ursinus) can be viewed as a natural experiment to investigate the nature of these primates mental representations of large-scale space. During a 16-month field study in a high population density habitat we recorded the foraging routes and the most important resources of a group of 25 individuals. Also, we estimated the locations of additional baboon groups relative to the study group. Routes were less linear, travel speed was higher, and inter-resource distances were larger when other groups were present within 500 m of the focal group; thus, the study group avoided others by taking detours. We predicted that evasive manoeuvres would be characteristic of different possible orientation mechanisms, and compared them with our observations. We analysed 34 evasive manoeuvres in detail. In an area that lacked prominent landmarks, detours were small; larger detours occurred when resources were directly visible, or in the vicinity of a hill offering conspicuous landmarks. In areas without prominent landmarks, detours were along familiar routes and waiting bouts of up to 60 min occurred; on one occasion the study group aborted their entire day`s journey. We discuss these findings in the light of time and energy costs and suggest that the baboons lack the ability to compute Euclidean relations among locations, but use network maps to find their way to out-of-sight locations.