Consequences of foraging trip duration on provisioning behaviour and fledging condition of common murres Uria aalgae

Abstract

We examine the provisioning constraints of a pursuit‐diving seabird in a cold ocean regime by comparing the behaviour of common murres Uria aalge rearing chicks at two colonies in the Northwest Atlantic during 1998‐2000. Funk Island is the largest (340,000–400,000 breeding pairs) and most offshore (60 km) colony of common murres in eastern Canada. Seventy‐five percent of the Northwest Atlantic population of common murres breeds on this island. Great Island is one island within the Witless Bay Ecological Reserve, which is the second largest breeding aggregation (100 000 breeding pairs) and is located near‐shore (2 km). The primary forage fish species in Newfoundland waters is capelin Mallotus villosus, which spawns on or near coastal beaches during summer. Therefore, the two study colonies differ in their distance to food resources and colony size. It is within this natural context that we compare: (1) prey types and frequency of delivery (amount of prey), (2) parental time budgets, and (3) the mass and condition (mass/wing length) of fledglings at both colonies. Similarly sized female capelin (100–150 mm) were delivered to chicks at both colonies. Foraging time per day per parent, a proxy of foraging effort, was similar at both colonies (Great Island: 5.1 h; Funk Island: 5.5 h), as was the percentage of time spent with mates (Great Island: 12.3%; Funk Island: 10.9%). Foraging trips, however, were longer at Funk Island (4.1 h) than at Great Island (2.9 h). This resulted in lower feeding rates of chicks (0.17 feeds per h) and poorer condition of fledglings (2.9 g/mm) at Funk Island compared to those at Great Island (0.22 feeds per h; 3.9 g/mm). We hypothesize that provisioning efforts are constrained at Funk Island by (1) distant food resources and increased competitor density, resulting in longer foraging trip durations and (2) the time spent paired with mates at the colony, which may reflect a minimum time required to maintain breeding sites due to higher breeding densities at Funk Island compared to Great Island. Demographic consequences of this poor fledgling condition at Funk Island are unknown, but fledglings may sufficiently accelerate growth at sea due to their closer proximity to an important nursery area. If fledgling survival is compromised, however, the lower potential for growth at Funk Island will impact the entire Northwest Atlantic population of common murres.

Foraging distance affects reproductive success in Magellanic penguins

“…If a penguin is away from the nest too long during incubation, the incubating mate may abandon the eggs to forage for itself, or the chicks may hatch and starve before the foraging parent returns with food (Yorio & Boersma 1994, Boersma & Stokes 1995, Otley et al 2004. During chick rearing, longer trips mean less frequent feeding of chicks, slower growth, and higher risk of starvation or low fledging weights (Davoren & Montevecchi 2003). The major cause of mortality for Magellanic penguin chicks is starvation (Boersma & Stokes 1995), and lone chicks grow more rapidly than chicks with siblings, suggesting that food is limited for Magellanic penguins (Boersma 1992).…”

“…Boersma et al (in press) found a nonlinear relationship between trip distance and duration, with penguins spending more time in foraging areas farther from the colony. If foraging trips take longer, offspring will be fed less frequently, resulting in slower growth rates and lower weights at fledging or weaning (Kitaysky et al 2000, Davoren & Montevecchi 2003. Longer travel distances also require increased energy expenditure that may affect adult body condition (Arnould et al 1996) and the balance between food assimilated by the adult and that delivered to offspring (Weimerskirch et al 1994, Ropert-Coudert et al 2004).…”

“…Longer foraging trips in years of low prey availability may cause increased investment in reproduction by adults (Boyd et al 1994) and decreases in offspring growth rates (Davoren & Montevecchi 2003, Pinaud et al 2005) and reproductive success (Inchausti et al 2003). Climate fluctuations may affect species differently, depending on prey and foraging strategies (Kitaysky et al 2000).…”

“…Oceanographic conditions vary from year to year, affecting the foraging locations and breeding success of marine central-place foragers, such as seabirds and pinnipeds, that feed at sea but breed on land (Boyd et al 1994, Kitaysky et al 2000, Sydeman et al 2001, Davoren & Montevecchi 2003. Foraging locations at sea, particularly distance to food, influence offspring feeding frequency (Pinaud et al 2005), reproductive success (Inchausti et al 2003), and adult energy balance (Shaffer et al 2003).…”

Foraging behaviour in two Antarctic fur seal colonies with differing population recoveries

“…In the face of reduced food resources many animals are known to adapt their time activity budgets (Hixon et al 1983, Furness & Birkhead 1984, Wanless et al 1992, Boyd 1999, Davoren & Montevecchi 2003, Harding et al 2007). This type of behavioural plasticity is a useful trait for marine predators living in a variable environment characterised by patchy and ephemeral food resources.…”