Time Budgets, Feeding Efficiency and Flock Dynamics in Mixed Species Flocks of Lapwings, Golden Plovers and Gulls

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Abstract
1. In mixed species flocks of lapwings and golden plovers, lapwing net rate of energy intake was positively related to the number of conspecifics and the amount of time individuals spent crouching during feeding, but was unaffected by the presence of golden plovers. Plover net rate of energy intake, however, was positively related to crouching tendency, negatively related to the number of lapwings present but unaffected by the number of conspecifics. 2. Golden plovers appeared to join lapwing flocks because they could then crouch more and scan less. The independent negative effect of lapwing number may have been due to feeding interference when there were large numbers of lapwings relative to plovers. 3. When black-headed gulls joined a flock, both lapwings and plovers tended to crouch less and take smaller worms. However, in lapwings these changes appeared to reduce feeding efficiency but plover net rate of energy intake increased as a function of the gull: plover ratio. 4. When gulls were present, the effect of conspecifics on lapwing feeding efficiency disappeared and the presence of plovers had a negative effect. Conversely, in plovers the presence of conspecifics enhanced feeding efficiency and the negative effect of lapwing number disappeared. 5. The arrival of gulls resulted in a decrease in equilibrium lapwing number but no consistent, directional change in plover number. When gulls were present, lapwing number tended to decrease when large numbers of plovers arrived, but increase when small numbers arrived. Increased lapwing number had no significant directional effect on plover number. Changes in lapwing and plover energy intake and species numbers are interpreted in terms of feeding interference and 'dilution' of gull kleptoparasitism. 6. In the absence of gulls, there was no significant directional relationship between increased plover number and lapwing number, but the presence of plovers generally correlated with a reduction in lapwing number. Plover number, however, decreased when large numbers of additional lapwings arrived but increased with small numbers of arrivals. Changes in species energy intake and numbers here are interpreted in terms of feeding interference and time budget changes. 1. In mixed species flocks of lapwings and golden plovers, lapwing net rate of energy intake was positively related to the number of conspecifics and the amount of time individuals spent crouching during feeding, but was unaffected by the presence of golden plovers. Plover net rate of energy intake, however, was positively related to crouching tendency, negatively related to the number of lapwings present but unaffected by the number of conspecifics. 2. Golden plovers appeared to join lapwing flocks because they could then crouch more and scan less. The independent negative effect of lapwing number may have been due to feeding interference when there were large numbers of lapwings relative to plovers. 3. When black-headed gulls joined a flock, both lapwings and plovers tended to crouch less and take smaller worms. However, in lapwings these changes appeared to reduce feeding efficiency but plover net rate of energy intake increased as a function of the gull: plover ratio. 4. When gulls were present, the effect of conspecifics on lapwing feeding efficiency disappeared and the presence of plovers had a negative effect. Conversely, in plovers the presence of conspecifics enhanced feeding efficiency and the negative effect of lapwing number disappeared. 5. The arrival of gulls resulted in a decrease in equilibrium lapwing number but no consistent, directional change in plover number. When gulls were present, lapwing number tended to decrease when large numbers of plovers arrived, but increase when small numbers arrived. Increased lapwing number had no significant directional effect on plover number. Changes in lapwing and plover energy intake and species numbers are interpreted in terms of feeding interference and 'dilution' of gull kleptoparasitism. 6. In the absence of gulls, there was no significant directional relationship between increased plover number and lapwing number, but the presence of plovers generally correlated with a reduction in lapwing number. Plover number, however, decreased when large numbers of additional lapwings arrived but increased with small numbers of arrivals. Changes in species energy intake and numbers here are interpreted in terms of feeding interference and time budget changes.