MIGRATION CHRONOLOGY AND DISTRIBUTION OF REDHEADS ON THE LOWER LAGUNA-MADRE, TEXAS

An estimated 80% of redheads (Aythya americana) winter on the Laguna M adre of southern Texas and Mexico. Because there have been profound ch anges in the Laguna Madre over the past three decades and the area is facing increasing industrial and recreational development, we studied the winter distribution and habitat requirements of redheads during tw o winters (1987-1988 and 1988-1989) on the Lower Laguna Madre, Texas t o provide information that could be used to understand, identify, and protect wintering redhead habitat. Redheads began arriving on the Lowe r Laguna Madre during early October in 1987 and 1988, and continued to arrive through November. Redhead migration was closely associated wit h passing weather fronts. Redheads arrived on the day a front arrived and during the following two days; no migrants were observed arriving the day before a weather front arrived. Flock size of arriving redhead s was 26.4 +/- 0.6 birds and did not differ among days or by time of d ay (morning midday, or afternoon). Number of flocks arriving per 0.5 h interval (arrival rate) was greater during afternoon (21.7 +/- 0.6) t han during morning (4.3 +/- 1.2) or midday (1.5 +/- 0.4) on the day of frontal passage and during the first day after frontal passage. Upon arrival, redhead flocks congregated in the central portion of the Lowe r Laguna Madre. They continued to use the central portion throughout t he winter, but gradually spread to the northern and southern ends of t he lagoon. Seventy-one percent of the area used by flocks was vegetate d with shoalgrass (Halodule wrightii) although shoalgrass covered only 32% of the lagoon. Flock movements seemed to be related to tide level ; redheads moved to remain in water 12-30 cm deep. These data can be u sed by the environmental community to identify and protect this unique and indispensable habitat for wintering redheads.