The calculating cormorants

Traditional fishing with captive cormorants was observed on the Li-Kiang River. After catching seven fish the birds were allowed to eat the eighth. Without this reward they refused to fish again. These birds could apparently count up to seven.     

Hormonal Regulation of Morphogenesis and Cold-resistance: II. EFFECT OF COLD-ACCLIMATION AND OF EXOGENOUS ABSCISIC ACID ON GIBBERELLIC ACID AND ABSCISIC ACID ACTIVITIES IN ALFALFA (Medicago sativa L. SEEDLINGS

The endogenous levels of gibberellin and abscisic acid weredetermined in extracts from seedlings of alfalfa (Medicago sativaL.) ov. Hairy Peruvian and cv. Ranger, growing under long daysand high temperatures (not inducing cold-hardiness), or shortdays and low temperatures (inducing cold-hardiness). Under inductiveconditions only Ranger was coldacclimated, exhibiting a rosettegrowth; non-acclimated seedlings of Ranger and Hairy Peruviandeveloped an elongated shoot. Under non-inductive conditionsgibberellin A₃ (GA₃)-like activity was found in both cultivars.Under inductive conditions GA3-like activity increased in HairyPeruvian and was almost non-existent in Ranger. In spite ofmorphological modification, ABA-like activity was hardly affectedby thermophotoperiod conditions. Addition of ABA to the nutrientsolution of seedlings growing under non-inductive conditionssimulated the effects of short days and of low temperatures.It diminished GA3 content, and affected morphological modificationof the seedlings. It is concluded that the modification of theABA/GA balance, through the decrease of the GA level, monitorsthe capacity of the twoalfalfa cultivars to become cold-acclimatedwhen exposed to low temperatures.     

Patterns of seasonal and yearly mass variation in West African tropical savannah birds

Birds in the northern hemisphere usually increase mass reserves in response to seasonal low temperatures and shorter day length that increase foraging unpredictability and so starvation risk. In the lowland tropics, relatively low temperatures and short day lengths are absent and so the risk of starvation may be reduced, leading to much smaller seasonal effects on mass. Nevertheless, other factors such as high temperatures and water and food availability may vary greatly between tropical wet and dry seasons, leading to variable starvation risk and seasonal mass effects. Using data collected from 47 species of birds caught over a 10‐year period in a tropical savannah region in West Africa we tested for seasonal variation in mass in response to a predictable, strongly seasonal tropical climate. Many species (91%) showed seasonal variation in mass, and this was often in a clear annual pattern that was constant across the years. Many species (89%) varied their mass in response to seasonally predictable rainfall. Annual variation in mass was also important (45% of species). Relatively few species (13%) had a seasonal pattern of mass variation that varied between years. Feeding guild or migratory status was not found to affect seasonal or annual mass variation. Seasonal mass change was on average 8.1% across the 21 species with a very large sample size and was comparable with both northern and southern temperate species. Our study showed that biologically significant consistent seasonal mass variation is common in tropical savannah bird species, and this is most likely in response to changing resource availability brought about by seasonal rainfall and the interrupted foraging response due to the constraints of breeding.