There is a swallow in coastal Peru that resembles the mangrove swallow, but lacks the white head stripe. It is possibly a subspecies, but the geographical separation suggests that this little known form is a distinct species.
The mangrove swallow’s bulky cup nest is built in natural or artificial cavities near water, usually below 2 m in height. Sites include tree holes and crevices in rock or bridges. The clutch is three to five white eggs which hatch in 17 days. The nestlings are fed by both parents for 23–27 days to fledging. Like the related tree swallow, this species is very aggressive to other hirundines when breeding, and nests are several hundred metres apart.
This swallow averages 13 cm (5 inches) long and weighs about 14 g. The bill is small and black. The adult mangrove swallow has iridescent blue-green upperparts, white underparts and rump, and blackish tail and flight feathers. There is a thin white stripe from the bill to above the eye. The female usually has duller colours than the male, and the juvenile is dull grey-brown above and grey-brown washed white below.
This species is closely associated with fairly still open water, and is often found in small flocks over rivers or lakes when not breeding. The mangrove swallow subsists primarily on a diet of insects, including large species such as dragonflies and bees.
The flight of the mangrove swallow is typically direct and low over the water. It frequently perches. Its call is a rolled jeerrrt.
- Stiles and Skutch, A Guide to the Birds of Costa Rica ISBN 0-8014-9600-4
- Turner, Angela K; Rose, Chris (1989). A Handbook to the Swallows and Martins of the World. Christopher Helm. ISBN 0-7470-3202-5.