The effect of food supplementation on the reproductive success of Black‐billed Magpies Pica pica

Abstract

The effect of supplementary food on the reproductive success of Black‐billed Magpies Pica pica was studied in an urban habitat in the city of Edmonton, Alberta, Canada. We provided supplementary food (pelleted dog food) regularly from August 1986 to June 1988 in a feeder situated outside all known magpie territories. Magpies using the supplementary food showed (i) an advancement of 7 days in the initiation of laying, (ii) no increase in clutch‐size, (iii) higher survival of nest contents (eggs and young) during a spring snow storm, (iv) an increase in rate of nestling weight gain, and (v) an increase in fledging success. Supplementary food did not prompt the fed pairs to select nest sites nearer the feeder in 1988 than in 1987. The feeder did not affect the breeding density because the nearest neighbour distances of fed magpies did not differ from unfed magpies in either year, nor did they differ between the two years for either fed or unfed magpies. This study provided evidence that magpies frequently renest even if their initial nests fail after the eggs hatch—a practice that has been reported to be absent or rare in other studies. Although brood reduction was equally frequent in the nests of food‐supplemented and control pairs, the actual number of nestlings disappearing from the former (1.56 per nest) was significantly smaller than that from the latter (2.60 per nest), suggesting that the availability of food plays a major role in magpie reproductive success.

Nest-predator prevalence along a mountain birch - alpine tundra ecotone

“…Corvids, in contrast, have the ability to habituate to humans and are likely to search for subsidies (i.e. leftover food and garbage) provided by recreationalists using the foot paths connected to cabin-resort areas (Dhindsa and Boag 1990;Taugbøl et al 2001).…”

“…External subsidies represent an input of energy and nutrients, which could have an impact on the ecosystem structure and function, thus potentially resulting in trophic cascades, such as increased spatial and temporal abundance of generalist predators (i.e. red fox and corvids), possibly leading to higher predation pressure (Dhindsa and Boag 1990;Pedersen et al 2007).…”

The Relationship Between Parental Defense Intensity and Nest Site Characteristics in Eurasian Magpie (Pica Pica L.) - An Assessment With the Classification Methods

“…In other words, parents could spend a more successful breeding process while the environmental conditions are in favor of them. For example, in black-billed magpies foodsupplemented parents gaining more time and energy for guarding nestlings had high reproductive success (Högstedt, 1981;Dhindsa and Boag, 1990). Similarly, Eurasian magpies breeding in urban environments can adjust the advantage of environmental conditions, the lack of intensely predation pressure, presence of favorable circumstance temperature and food abundance with anthropogenic nutrients to their reproductive output (Jerzak, 2001; Yamaç and Kirazlı, 2012).…”

“…Limited food supply is one of the most important reasons of nest failure and high bird mortality rate (Högstedt, 1981), and thus there is a significant relation between food abundance and availability, and survival success of nestlings and breeding success (Yom-Tov, 1974; Högstedt, 1981; Dhindsa and Boag, 1990; Rastogi et al, 2006;Harrison et al, 2010). Food availability can also lead to a change aggressive behavior of parents like food supplemented parents increased nest attentiveness in response to guard their investments, and exhibited riskier defense behavior (Högstedt, 1981;Dhindsa and Boag, 1990;Rytkönen, 2002;Rastogi et al, 2006). Additionally, according to a predation risk assessment (see Fontaine and Martin, 2006;Dassow et al, 2011), if the threat of predation varies along the urbanization stages (Eden, 1985;Rodewald et al, 2011) then parents' nest defense strategies can be modified with respect to this.…”

“…Accordingly, nest volume is the primary factor indicating the willingness of parents to invest in nest defense as it might be expected. In magpies, the strategy of parental investment shaping by many factors like other bird species such as age, sex, residual reproductive value of parents, reproductive value of offspring, food availability, predator pressure and habitat connectivity (Baeyens, 1981a;Högstedt, 1981;Eden, 1985;Redondo and Carranza, 1989;Dhindsa and Boag, 1990;Kang et al, 2012), seem to be initially influenced by own capacities and conditions. Nevertheless, parents pick up information particularly about offspring condition (the number of clutch/brood/fledgling reduction), and strongly adjust investment according to the reproductive value linking survival chance of offspring over the breeding period (Redondo and Carranza, 1989).…”