Lower foraging efficiency of offspring constrains use of optimal habitat in birds with extended parental care

TY - JOUR

T1 - Lower foraging efficiency of offspring constrains use of optimal habitat in birds with extended parental care

AU - Nolet, B.A.

AU - Gyimesi, A.

AU - van Lith, B.

N1 - Reporting year: 2014 Metis note: 5564, AnE Data archiving: data archived at MDA

PY - 2014

Y1 - 2014

N2 - Keywords: food intake rate; giving-up density; habitat switch; parental costs; social dominance After reproducing successfully, birds with extended parental care form family groups. Despite being the dominant social unit, such family groups have been reported to switch to alternative habitat earlier than adults without offspring, with potential negative carry-over effects for the next breeding season. Here we test a proposed mechanism for this earlier habitat switch, namely a low foraging efficiency in juveniles. Such a test is best performed under controlled conditions because in the field families may occupy food patches of a different quality than singles or pairs without young. We studied this mechanism in Bewick's Swans Cygnus columbianus bewickii, which trample (or ‘treadle’) for food buried in the sediment. The gross intake rate of juveniles was as low as 60% of that of adults, depending on the burial depth of the food. Trampling effort did not differ between age classes, but differences in intake rate were related to body size, suggesting that larger or heavier birds were trampling more efficiently. Corresponding giving-up densities in the field were calculated to be c. 60% higher for juveniles than for adults. Our findings are consistent with the hypothesis that the lower foraging efficiency of juveniles may be responsible for the segregation of family groups from adults without offspring.

AB - Keywords: food intake rate; giving-up density; habitat switch; parental costs; social dominance After reproducing successfully, birds with extended parental care form family groups. Despite being the dominant social unit, such family groups have been reported to switch to alternative habitat earlier than adults without offspring, with potential negative carry-over effects for the next breeding season. Here we test a proposed mechanism for this earlier habitat switch, namely a low foraging efficiency in juveniles. Such a test is best performed under controlled conditions because in the field families may occupy food patches of a different quality than singles or pairs without young. We studied this mechanism in Bewick's Swans Cygnus columbianus bewickii, which trample (or ‘treadle’) for food buried in the sediment. The gross intake rate of juveniles was as low as 60% of that of adults, depending on the burial depth of the food. Trampling effort did not differ between age classes, but differences in intake rate were related to body size, suggesting that larger or heavier birds were trampling more efficiently. Corresponding giving-up densities in the field were calculated to be c. 60% higher for juveniles than for adults. Our findings are consistent with the hypothesis that the lower foraging efficiency of juveniles may be responsible for the segregation of family groups from adults without offspring.

KW - NIOO

U2 - 10.1111/ibi.12137

DO - 10.1111/ibi.12137

M3 - Article

SN - 0019-1019

VL - 156

SP - 387

EP - 394

JO - Ibis

JF - Ibis

IS - 2

ER -