Female Magpie quality can be used to explain over 60% of the variance in clutch-size and size of eggs laid during the breeding season. Male quality accounts for over 70% of a pair’s breeding success within each breeding season. The differential ability of males to provision their female adequately during incubation and their chicks in the nestling period is the most likely explanation for this result. The timing of breeding for the Magpie appears to be controlled primarily by territory quality, but the effect is relatively weak (only 19%). Although no effect of female quality on the timing of breeding was detected, this cannot be totally discounted. In addition, it is likely that environmental constraints (i.e. temperature) also exert some influence on the date of egg laying (Goodburn 1991).
When supplied with additional food before breeding, experimental pairs of Magpie’s started egg-laying earlier, had larger clutches, heavier eggs, and greater hatching success, and produced more fledglings than control pairs. Food did not, however, attract new settlers to empty territories. Experimental pairs not only laid earlier, but they also started their laying within a significantly shorter period of time than did controls. The relatively small-scale effects of extra food on timing of breeding suggest that food alone does not determine start of laying, but that it is also stimulated by some other factors. Shortly after the additional factors were perceived by the birds, laying started. As experimental birds were in a better nutritional state than controls, they responded faster, laid larger clutches and heavier eggs. The difference in reproductive success between the two groups was established during the nestling phase. Predation, mainly by hooded crows Corvus cornix L., and starvation, especially during adverse weather, causes bird mortality. As invertebrate activity decreases in such periods, food scarcity is suggested to be the ultimate mortality factor. Extra food given acts to buffer adverse periods, giving a more stable temporal distribution of food as compared with natural conditions (Hogstedt 1981).
Magpies are corvids, which belong to the order of Passeriformes, a phylogenetic group characterized by large brains relative to body weight. The relative brain size of passeriform birds is similar to primates in allometric analyses, and within the Passeriformes, corvids stand out with particular high relative brain size. Thus, magpies belong to a group of animals with very high relative brain size. Mammals and birds inherited the same brain components from their last common ancestor nearly 300 million years ago and have since then independently developed a relatively large forebrain pallium. However, both classes differ substantially with regard to the internal organization of their pallium, with birds lacking a laminated cortex but having developed an organization of clustered forebrain entities instead. In some groups of birds and mammals, such as corvids and apes, respectively, brain to-body ratios are especially high and these animals are able to generate the same complex cognitive skills. This is indicated by feats such as tool use and tool manufacture episodic-like memory and the ability to use own experience in predicting the behavior of conspecifics. Magpies are food-storing corvids that compete with conspecifics for individually cached and memorized hoards. They thus live under ecological conditions that favour the evolution of social intelligence. They achieve the highest level of Piagetian object permanence, which is also achieved by apes, but not by monkeys. In this experiment, magpies were capable of understanding that a mirror image belongs to their own body. This experiment shows that magpies respond in the mirror and mark test in a manner so far only clearly found in apes, and, at least suggestively, in dolphins and elephants. This is a remarkable capability that is at least a prerequisite of self-recognition and might play a role in perspective taking (Prior et al. 2008).
- Goodburn.F.S., (1991) Territory quality or bird quality? Factors determining breeding success in the Magpie (Pica pica). IBIS, 133, 85-90.
- Hogstedt.G., (1981) Effect of Additional Food on Reproductive Success in the Magpie (Pica pica). Journal of Animal Ecology, 50, 219-229.
- Prior.H., Schwarz.A., & Gunturkun.O., (2008) Mirror-Induced Behaviour in the Magpie (Pica pica): Evidence of Self-Recognition. PLoS Biology, 6, 1642-1650.