Body mass patterns of Little Stints at different latitudes during incubation and chick‐rearing

Abstract

Due to the ‘double‐clutch’ mating system found in the arctic‐breeding Little Stint Calidris minuta, each parent cares for a clutch and brood alone. The resulting constraint on feeding time, combined with the cold climate and a small body size, may cause energetic bottlenecks. Based on the notion that mass stores in birds serve as an ‘insurance’ for transient periods of negative energy balance, but entail certain costs as well, body mass may vary in relation to climatic conditions and stage of the breeding cycle. We studied body mass in Little Stints in relation to breeding stage and geographical location, during 17 expeditions to 12 sites in the Eurasian Arctic, ranging from north Norway to north‐east Taimyr. Body mass was higher during incubation than during chick‐rearing. Structural size, as estimated by wing length, increased with latitude. This was probably caused by relatively more females (the larger sex) incubating further north, possibly after leaving a first clutch to be incubated by a male further south. Before and after correction for structural size, body mass was strongly related to latitude during both incubation and chick‐rearing. In analogy to a similar geographical pattern in overwintering shorebirds, we interpret the large energy stores of breeding Little Stints as an insurance against periods of cold weather which are a regular feature of arctic summers. Climate data showed that the risk of encountering cold spells lasting several days increases with latitude over the species’ breeding range, and is larger in June than in July. Maintaining these stores is therefore less necessary at southern sites and during the chick‐rearing period than in the incubation period. When guarding chicks, feeding time is less constrained than during incubation, temperatures tend to be higher than in the incubation period, reducing energy expenditure, and the availability of insect prey reaches a seasonal maximum. However, the alternative interpretation that the chick‐tending period is more energetically stressful than the incubation period, resulting in a negative energy balance for the parent, could not be rejected on the present evidence.

Body mass dynamics during incubation and duration of parental care in Pacific Dunlins Calidris alpina pacifica: a test of the differential parental capacity hypothesis

“…The amount of care provided by the female varies with date (Jamieson ) and parental body mass can decline rapidly at the time of hatching (Tulp et al . ). Body mass can also vary diurnally (Szentirmai et al .…”

Time allocation between feeding and incubation in uniparental arctic‐breeding shorebirds: energy reserves provide leeway in a tight schedule

“…The effect of incubation stage (day relative to hatching) was also tested. Weights obtained on the day prior to or on the hatching date were excluded, because a sudden drop in body mass linked to hatching of the chicks commences around that day (Soloviev and Tomkovich 1997, Tulp et al 2002). Too few PS and RP were caught for this analysis.…”

Body condition of shorebirds upon arrival at their Siberian breeding grounds

“…Small shorebirds, particularly those in which one adult incubates alone (e.g. Little Stint and Curlew Sandpiper) need stores to endure bad weather periods during breeding (Tulp et al 2002;Tulp and Schekkerman 2006). Arrival with some stores remaining can give them a head start.…”