Foraging distance affects reproductive success in Magellanic penguins

Abstract

Foraging distance affects reproductive success and other demographic parameters in seabirds and pinnipeds. We tracked breeding Magellanic penguins Spheniscus magellanicus at Punta Tombo, Argentina using satellite transmitters from 1996 to 2006 (n = 148 males, 57 females) to investigate the variability in foraging distance and its effects on reproductive success. The time a penguin was away from its nest predicted the distance it swam during all stages of the breeding season (p < 0.005); this relationship was linear during incubation and nonlinear during chick rearing. During incubation, penguins went 1.0 km farther from the colony for every additional hour they were away from the nest, and the distance penguins traveled predicted the mean colony reproductive success. When chicks were > 30 d old, the probability of fledging 2 chicks was highest when penguins went less than 70 km from their nests. Penguins that went between 70 and 180 km from their nests were most likely to raise one chick, and the probability of losing both chicks increased with trip distance. Females and males made trips of similar distance. Foraging-trip distance varied within breeding season (p < 0.005). Penguins went farthest during incubation (411 ± 11.8 km), and stayed closest (61 ± 3.9 km) when chicks were < 30 d old, requiring parents to guard them. When chicks were older, adults traveled 111 ± 5.0 km. Mean foraging-trip distance varied among years (p < 0.005) by factors of 1.5 to 1.8, and trips by an individual penguin varied by a factor of 22.

Natural selection on morphology varies among years and by sex in Magellanic Penguins (Spheniscus magellanicus)

“…Additionally, we detected no selection on any traits for males in most years (21 of 28 yr) with the lowest chick starvation, which suggests that when ample food is available, size may not be an important determinant of reproductive success. Predation, climatic events, nesting density, fights, and foraging distance (see Stokes and Boersma 1998, 2000, Boersma and Rebstock 2009 can also affect reproductive success in Magellanic Penguins. Similar environmental variables influence selection of traits in other birds, including weather (Brown and Brown 1998), food size (Boag and Grant 1981), and human interference (Brown and Brown 2013).…”

“…We expected all traits (including body size) to be heritable and subject to selection because each of the 4 traits independently as well as overall body size are important for the survival and reproductive success of both sexes. We hypothesized that selection on each trait and on body size would be temporally variable because environmental conditions and reproductive success vary among years (Boersma 2008, Boersma and Rebstock 2009, and a long-term study on natural selection in Darwin's finches showed temporally variable selection (Grant and Grant 2002). The present study, to our knowledge, is the first long-term study of natural selection on morphology in a seabird and is one of only a few long-term selection studies on morphology in birds (see Grant and Grant 2002).…”

“…Flippers are used for propelling penguins through the water (Davis and Renner 2003) and allow penguins to catch prey and avoid predators, so flipper size may be most important for overall fitness. Additionally, Magellanic Penguins migrate long distances (Stokes et al 2014) and are traveling farther to find prey than they did a decade ago (Boersma and Rebstock 2009), so even slightly longer flippers may benefit individuals. Feet are used as rudders and are important for foraging because they provide maneuverability (Davis and Renner 2003).…”

Stop-loss order for forage fish fisheries

“…Long-term empirical studies have demonstrated that seabird breeding success (and ultimately population size) declines precipitously as the abundance of their forage fish prey decreases and foraging time increases (9,10). Simulations using ecosystem models indicate that impacts on dependent predators were substantially reduced as the minimum biomass threshold of their forage fish prey increased (2).…”

Intercolony variations in movement patterns and foraging behaviors among herring gulls (Larus argentatus) breeding in the eastern Wadden Sea

“…Prey depletion may imply long flight distances with higher trip costs and an increased risk of nest predation (Morris & Black, 1980; Pierotti & Annett, 1991). Prey availability in the vicinity of the breeding place is thus a “key” factor determining foraging success (Boersma & Rebstock, 2009; Isaksson et al., 2016; Rogers, Piersma, & Hassell, 2006). Tidal flats are visited by herring gulls, as well as by other gull species and a variety of waders, but are only temporarily available for foraging because of tidal water coverage, and previous studies demonstrated both inter‐ and intraspecific competition on tidal flats (Tiedemann & Nehls, 1997).…”