Flight speeds observed with radar, a correction: slow ?birds? are insects

Abstract

Based upon new data and re-analysis of previous data, some results concerning migration of " b i r d s " at night are now attributed to insects. In particular, slowly flying radar targets over land (Larkin and T h o m p s o n 1980) and, by analogy, over the ocean (Larkin et al. 1979) are shown to lack wing beat patterns of birds and the appearance of birds when viewed with a radar-controlled high-power telescope and spotlamp. The insect targets overlap with birds in the amount of radar echo returned, are abundant in warmer months, and fly even in March and November in temperate North America. Other previous results are largely substantiated; however, a previous report (Larkin 1980) that migrating birds can detect the wind direction over the ocean is not substantiated.

Comparaison entre un dénombrement de passereaux en migration nocturne et la réflectivité d'un radar de surveillance météorologique canadien /

“…Furthermore, additional noise may originate from echoes produced by non-passerine birds (e.g., geese and shorebirds in this study) and insects (Larkin 1991). This may also explain why the mode!…”

“…Considering that passerines fly at an average of 10-12 m/s (Larkin 1991) and that the most distant pixel sampled was 7 km from the field station, birds could take between 9.7 and 11.7 min to cover this distance. Because some birds were thus counted before they reached the area in which reflectivity was measured, we also fitted the same models as above (Tabte 2) but with the reflectivity measured in the following 10-min period (Z M ).…”

High passage rates and different seasonal migration strategies of birds along the lower Texas coast

“…When the proportion of non-bird targets comprised >10% of the targets recorded for that hour, the hour was removed in the vertical radar dataset (Mabee et al, 2006). Birds and bats may overlap in air speeds which presents a problem in radar studies to classify targets as birds or bats (Larkin, 1991;Bruderer and Boldt, 2001;Kunz et al, 2007). Bats exhibit erratic flight patterns when foraging and this behavior may aid in discriminating between bats and birds (Kunz et al, 2007).…”

Concentrated Migratory Morning Flight at Lake Pontchartrain, Louisiana, USA

“…If the radial airspeed was less than 5 m sec À1 (i.e. the PV may have been dominated by slow-moving insects; Larkin 1991, Gauthreaux and Belser 1998, Buler and Dawson 2014, the PV was classified as containing nonbird targets and the reflectivity in that PV was set to zero. Our data on wind speed were from NARR, which models wind velocity and direction every 3 hr on a threedimensional grid of points covering North America.…”